THYROID GLAND ABSORBED RADIATION DOSE …lib.ugent.be/fulltxt/RUG01/001/376/223/RUG01-001376223_2010_0001... · THYROID GLAND ABSORBED RADIATION DOSE FROM INTRA-ORAL RADIOGRAPHS IN

MSc DMFR – Johan K.M. Aps - 2008

1

THYROID GLAND ABSORBED RADIATION

DOSE FROM INTRA-ORAL RADIOGRAPHS IN

CHILDREN WHO SUFFERED A DENTO-

ALVEOLAR TRAUMA

Author

Johan Karel Maria APS

DDS, MSc Paed. Dent., PhD

Research Assistant Professor Ghent University, Dental School

Senior Consultant Ghent University Hospital, Dental School and Dental out-patient clinic

Year of submission of this thesis : 2008


2


3

THYROID GLAND ABSORBED RADIATION DOSE FROM INTRA-ORAL RADIOGRAPHS IN

CHILDREN WHO SUFFERED A DENTO-ALVEOLAR TRAUMA

“ A project report submitted in partial fulfillment of the Master of Science degree in

Dental and Maxillofacial radiology from the University of London. Unit of Distance Learning,

King’s College London Dental Institute.”


4

Dedication

This work is dedicated to my wife, Myriam, and our two daughters, Nathalie and Charlotte,

who have been patiently enough to let me achieve this, while I had a fulltime professional

task at the Ghent University and the Ghent University Hospital and not to forget being a

husband and “dad”. It has not been “easy” for you.

Thank you very much for this opportunity, my dear “girls”.


5

Abstract

Children who suffered a dento-alveolar trauma are subjected to an initial radiographic

examination and in most cases follow-up radiographs are necessary. However, the angle of

projection, particularly in children under the age of 10 and under critical conditions,

frequently put the thyroid gland in the path of the X-ray beam.

The first aim of the present study was to evaluate the available literature of 1998 to June

2008 on thyroid gland absorbed dose from intra-oral radiography, with a focus on children.

Secondly, assessment of the number of radiographs per dento-alveolar trauma case in the

Ghent University Dental Outpatient Clinic in children aged 1 till 18 years old. Thirdly, a

retrospective assessment, by means of Personal Computer X-ray Monte Carlo calculations

(PCXMC® version 1.5), of the absorbed radiation dose by the thyroid gland from intra-oral

and occlusal radiographs of the maxillary incisors, based on the projection angles, derived

from the radiographs from the Ghent University Dental Outpatient Clinic.

From the clinical data it was observed that in children younger than 5 years, the occlusal

radiograph was used in 87% of cases. For children older than 5, several projection

techniques were used in equal proportions. Three projection angles, 30°, 45° and 65°

respectively, were further used for PCXMC® calculations. It was found that irrespective of

the exposure settings, the absorbed dose by the thyroid gland decreased with age and that

there were significant differences between ages (1, 5, 10, 15 and 20 year olds). A projection

angle of 45° caused a significantly higher absorbed dose by the thyroid gland than did 30° or

65°. Therefore the routine use of a thyroid radiation protection shield is recommended in

order to reduce the dose to the thyroid gland.


6

Furthermore similar calculations were executed by means of the PCXMC® version 2.0 in

which the weighting factor for the salivary glands was included (ICRP 2005 guidelines).

Besides the obvious absorbed dose by the salivary glands, it was observed that the dose

absorbed by the thyroid gland was lower when estimated with PCXMC® version 2.0.

Therefore, prudence should be called when comparing estimated values from different

PCXMC® versions.


7

Contents

Chapter 1…………………………………………………Introduction………………………………p 10.

Chapter 2…………………………………………………Aims of the study………………………p 25.

Chapter 3…………………………………………………Material and Methods………………p 27.

Chapter 4…………………………………………………Results of literature search……….p 30.

Chapter 5…………………………………………………Results of clinical data……………….p 44.

Chapter 6…………………………………………………Results of PCXMC calculations…..p 50.

Chapter 7…………………………………………………Discussion………………………………….p 74.

Chapter 8…………………………………………………Conclusion…………………………………p 79.

References ………………………………………………………………………………………………….p 80.

Addendum 1………………………………………………………………………………………………..p 84.


8

Acknowledgements

I wish to thank Dr. Suk Ng for her guidance since the first year of the MSc. Her thrive was

contagious and I hope to be as inspiring to my own students and colleagues in the future. I

also wish to thank everyone who was involved in the four years of the MSc for their good

work in teaching.

My appreciation to Dr. Klaus Bacher of the Ghent University, dept. of Medical Radiation

Physics, who was helpful with guiding me into the PCXMC® calculation software.

I also wish to express my gratitude to the staff of the Ghent University Dental School to

provide the financial opportunity to let me follow this interesting MSc course, which will

hopefully lead to the development of a successful medical imaging department at the Ghent

University Dental School and Ghent University Dental Out-Patient Clinic .

I also, of course, wish to thank my colleagues of the Department of Paediatric Dentistry of

the Ghent University Dental School, for adapting their work schemes to my MSc schedule for

the past 4 years. As one of them once said at a time of the department’s internal reflection

moments; “what seems right for the School is maybe not that right for the Department and

vice versa”. I agree, but in this case this statement may be shown wrong, as this thesis will

be useful for the Department and for the School.

I want to express my gratitude to two new friends of mine who provided the perfect

environment to study while I was in London. Thank you David and Chris for all you have done

for me and for having me in your house the past 4 years.


9

Last but not least, I have to thank my parents, who always taught me to go beyond my

apparent limits and my wife and children for supporting me in this project of 4 years of

extra studying. Without them, I would never have achieved this. Thank you very much!


10

CHAPTER 1 : Introduction

Diagnostic information can be retrieved from the patient through an anamnesis (history and

clinical examination) and medical imaging techniques. In dentistry, the latter is mostly

obtained using ionizing radiation. Non-ionizing radiation, namely, ultrasound imaging for

purely dental purposes (e.g. caries detection) is currently not available, but hopefully will in

the future. Intra-oral, as well as extra-oral radiological techniques, e.g. periapical

radiographs and dental panoramic tomography respectively, are being used frequently in

children, adolescents and adults.

Radiation administration is governed by three principles: the ethical justification of an

examination, the choice of equipment and procedural optimization and the ALARA principle.

This quote is from Regulla and Eder (2005)1 and comprises perfectly how every radiological

examination should be performed.

A study carried out in the UK2 in 2004, concerning the UK population radiation dose due to

medical exposures, showed that only 0.36% came from dental exposures (table 1). This is a

low percentage, however, one should take into account that this is an underestimation, as

retakes are probably not included in these calculations. The latter holds also for the other

medical exposures. Nevertheless, these figures are for the entire population, but it would be

a very interesting investigation, to calculate the dose for children under the age of 15. The

relative contribution of dental radiography in this age group may be substantial, compared

to dental exposures in the entire population. The latter may prove to be important, with

other dental radiographic techniques coming on the scene, such as cone beam CT, which


11

may be used in children as well, as it may be helpful in diagnosing problems in dento-

alveolar trauma.

Table 1. Contributions to UK collective dose (man Sv) from Hall and Wall, 20042.

Type of radiological examination Collective dose years

2001/2002 in man Sv

CT 10650

Interventional 1920

Conventional radiography 7720

Barium enema 2379

Abdomen 749

Lumbar spine 692

Pelvis 559

Mammography 513

Dental 82

Others 2746

Angiography 2423

TOTAL 22173

Frequency of radiographs taken is one thing, but exposure settings are equally important

when considering young individuals. A recent study by Hujoel et al., 20083, emphasized on

the fact that although the radiation dose used in dental radiography is relatively low, the

impact of the radiation dose should not be ignored for children, due to the number of


12

radiographs, and the associated effective dose. Their study focused on radiographs taken

during an entire orthodontic treatment. Nevertheless, their conclusion is also a plea for

being more careful when deciding to make another radiograph in young patients. They also

commented on the use of cone beam CT in orthodontic patients and the impact of that on

the patient’s absorbed dose. They estimated that if one episode (21 intra-oral peri-apicals, 3

cephalographic and 3 panoramic radiographs) was replaced by 2 cone beam CTs, the dose

for the thyroid gland and the red bone marrow would increase by 400 to 500%. This

significant increase should be borne in mind when referring young patients for these kind of

radiographs. The latter, obviously, is dependent on the type of cone beam CT machine that is

used (field of view size, kV, mA and exposure time).

A study by Angelieri et al., 20074, emphasized on the issue of potential cytotoxic effects from

diagnostic ionizing radiation, such as dental panoramic tomography, on the buccal epithelial

cells. This study stresses the fact that cytogenetic damage was not an issue for this kind of

low energy radiation, but that one should keep in mind that repeated exposure to cytotoxic

agents (also other than ionizing radiation) can result in chronic cell injury, compensatory cell

proliferation, cell hyperplasia and tumor development ultimately. Therefore caution should

be paid when irradiating children.

Looe et al., 20065, stress the importance of using child exposure settings when dealing with

children. Not only for the benefit of the image quality, but especially for the radiation dose

that should be kept as low as possible. The latter is important in the view of children

undergoing serial review radiographs for reasons of dental trauma follow-up. Regarding the

salivary glands and possible malignancy developing from radiation, the suggestion is made

that one could use a risk factor of 15% per Sv for children and a tissue weighting factor of


13

2.5% in assessing the risk of fatal cancer development due to dental radiography. However,

as this could lead to overestimation of the risk, the benefit would be that if everyone would

adhere to the dose reference limits (DRLs) for children, the risk of a fatal cancer developing

from dental radiation in childhood, would decrease to almost zero. This should be the

ultimate aim as there is no justification of exposing children to ionizing radiation in dentistry

knowing that there is a substantial risk to develop a fatal cancer. The thyroid gland, red bone

marrow, the brain and the salivary glands are those organs that should be exposed the least

to ionizing radiation, as it concerns particularly radiation sensitive tissues.

Dental and maxillofacial radiology makes up about 20% of all medical radiation a patient may

be subjected to. Nonetheless the absolute radiation dose of a dental radiographic procedure

is low, it is important to assess and minimize the risk for fatal cancers due to dental

radiological procedures, because of the high number of radiographs a patient may be

exposed to6. Especially in children, who are intrinsically very radiosensitive, because of the

nature of their tissues. In Table 2 the main acute effects following large whole body doses of

radiation are shown.

From table 2, it is obvious that dental radiation is never going to cause such effects, as the

doses are much lower (e.g. a peri-apical at 70kV, 0.10s exposure time, 8 mA and F-speed film

causes a patient absorbed dose of 0.001 mSv). Nevertheless ionizing radiation as being used

in dentistry should be handled with care and whole lifetime patient effective dose

calculations should be executed taking them into account.


14

Table 2. Main acute effects of whole body irradiation (source: E. Whaites, 20076)

Dose (Sv) Whole body effect

0.25 Nil

0.25-1.0 Slight blood changes, e.g. leukocyte count changes

1-2 Vomiting within 3 hours, fatigue, loss of appetite, blood changes – recovery

after a few weeks

2-6 Vomiting within 2 hours, severe blood changes, loss of hair within 2 weeks –

recovery within 1 month to a year for only 70%

6-10 Vomiting within 1 hour, intestinal damage, severe blood changes – death

within 2 weeks in 80 to 100% of cases

>10 Brain damage, coma and death

Table 3 shows an estimate of the chance to develop a fatal cancer from several different

dental radiation exposures.

Table 3 illustrates the very low risk of dental radiological examinations, especially when

intra-oral radiographs, with F-speed film exposed at 70 kV, are considered. However, one

should never forget the cumulative effect of radiation doses, no matter how low the

effective dose of a single exposure might be.


15

Table 3. Estimated risks of fatal cancer from 6 different dento-maxillofacial radiation

examinations (source: E Whaites, 20076).

X ray examination type Estimated risk of fatal cancer

BW/peri apical, 50kV, D-speed film and SFD=10cm 1 / 2 000 000

BW/peri apical, 70kV, F-speed film, SFD=20cm 1 / 20 000 000

Dental Panoramic Tomography 1 / 1 000 000

PA skull 1 / 670 000

Lat skull 1 / 2 000 000

CT skull 1/ 10 000

(BW = bitewing, SFD = skin –focus distance, PA = posterior-anterior, Lat = lateral, CT = computed tomography)

The figures in table 3 only account for an adult person of about 20 years old. In table 4 the

multiplication factors for different age groups are presented. From this table it becomes

immediately clear that the younger an individual, the higher the risk to develop a fatal

cancer due to ionizing radiation. The main reason is their higher radiosensitivity and the fact

that they live longer, what implies that a cancer has more chance to develop. These figures

show clearly that for children and adolescents, the risk is 200 to 300% higher than for a 20

year old person. This is important as in the follow up of a dental trauma, the patients are

often subjected to a high number of radiographs, taken from the same anatomical area,

which means that for each radiograph taken, the risk to develop a fatal cancer will increase.


16

Table 4. Multiplication factor for the risk to develop a fatal cancer because of ionizing radiation

(source: Selection criteria for dental radiography, 20047 and E. Whaites, 20076)

Age group (years) Multiplication factor

< 10y 3

10-20y 2

20-30y 1.5

30-50y 0.5

50-80y 0.3

>80y negligible

The nature of the tissues that are being irradiated also has to be taken into account, when

calculating the specific organ effective doses. Therefore a weighting factor for several

radiosensitive organs have been proposed by the International Commission on Radiation

Protection (ICRP) and recently adjusted.

Effective dose was first introduced in 1975 as a mechanism for assessing the radiation

detriment from partial body irradiations, by means of weighting factors for different organs.

These weighting factors were derived from the total body irradiation8. The basic dosimetric

quantity related to the probability of the appearance of stochastic radiation effects, as

defined by the ICRP, is the effective dose. The effective dose is the sum of the weighted

equivalent doses in all tissues and organs of the body. The following equation (equation 1)

can be used to calculate the effective dose9:


17

Equation 1. Universal formula to calculate effective dose.

E = Σ WT HT

(WT is the weighting factor for the tissue and HT is the equivalent dose in a tissue or organ)

(source; Kramer et al. 20039)

Table 5 shows the different tissue weighting factors according to the ICRP guidelines for

1990 and 2005. The weighting factor for the breasts was more than doubled in the latest

guidelines, while the weighting factor for the gonads was reduced to only 1/4th of the value

of the 1990 guidelines. On the other hand, brain, kidney and salivary glands were included in

the latest guidelines, though the weighting factor for these organs was kept very moderate

(0.01). The weighting factor for the remainder of tissues was doubled in the 2005 guidelines,

compared to the 1990’s.

According to the ICRP guidelines and as supported in a document published on the world

wide web (02/276/05 – 5 June 2006)10 the approximate overall risk coefficient for the

development of a fatal cancer due to ionizing radiation is 0.00005 per mSv.

The latter is for adults, so the age multiplication factors, as mentioned in table 4, should be

used to assess the risk for the different age groups. However, a little further in the same

document it is mentioned that the thyroid gland is a very radiosensitive organ, especially in

children, who are very vulnerable to thyroid cancer. The salivary glands are also ascribed a

tissue weighting factor (see table 5), but they are considered less radiosensitive than the

thyroid gland. The document also says that the values are the same for both genders and for

all age groups. It is also stressed that, nevertheless, low energy radiation (< 100 kV) is used


18

(e.g. intra-oral radiography), the local impact of the radiation, on the tissues irradiated (e.g.

skin, thyroid gland, salivary gland brain), may be substantial. The latter is supported by the

study of Angelieri et al., 20074.

Table 5. Tissue weighting factors (WT) according to the ICRP guidelines of 1990 and 2005.

Tissue WT (1990) WT (2005)

red bone marrow 0.12 0.12

breast 0.05 0.12

colon 0.12 0.12

lung 0.12 0.12

stomach 0.12 0.12

bladder 0.05 0.05

oesophagus 0.05 0.05

gonads 0.20 0.05

liver 0.05 0.05

thyroid 0.05 0.05

bone surface 0.01 0.01

brain 0.01

kidneys 0.01

salivary glands 0.01

skin 0.01 0.01

remainder 0.05 0.10


19

In dentistry the radiation energy is to be called very modest. Nevertheless, again because of

the, sometimes, high number of radiographs taken in a patient at the same site for follow-up

reasons for instance, the effective dose to which the patient is exposed may increase

substantially. In other words, the accumulative doses achieved by this have eventually a

substantial impact on the effective dose. Implication of tissue weighting factors (red bone

marrow, bone surface, thyroid gland, oesophagus, salivary glands, brain and skin in case of

dental and maxillofacial radiology) may then become of use, especially when it concerns

young individuals and/or tissues which are very radiosensitive.

The total effective dose (E) a patient has received can be calculated as the product of the

radiation absorbed dose (D), which is a measure of the amount of energy absorbed from the

radiation beam per unit mass of tissue, and a weighting factor of the type of radiation (WR)

used (for X-rays, WR = 1) and a weighting factor of the tissues being irradiated (WT)6,7, 11-13.

The product of D and WR is also expressed as equivalent dose (H). Equation 2. shows how

the effective dose can be calculated.

Equation 2. Calculation of the total effective radiation dose

E = D x WR x WT

H = D x WR

thus: E = H x WT (Unit = Sievert or Sv)

In table 6 effective doses from several radiological exposures are shown. The effective dose

of intra-oral radiography is indeed very low, compared to a CT of the maxilla, but once more,


20

it should be stressed that the impact of a high number of intra-oral radiographs should not

be neglected, especially when these are taken from the same area, particularly in young

individuals.

When considering these low doses from dental radiography and their impact on the

patient’s tissues, the biological effects from ionizing radiation should be assessed. Ionizing

radiation can cause somatic deterministic effects, somatic stochastic effects and genetic

stochastic effects.

Table 6. The effective dose of 11 different radiological examinations (source: E. Whaites,

20076).

Type of examination E (mSv)

CT chest 8.0

CT head 2.0

PA skull 0.03

Lat skull 0.01

PA chest 0.02

bitewing / peri apical 0.001-0.008

Upper Standard Occlusal 0.008

Dental Panoramic Tomography 0.004-0.030

Cephalography 0.002-0.003

CT mandible 0.36-1.2

CT maxilla 0.10-3.3


21

Somatic effects can be subdivided into acute (immediate) and chronic (after some time

occurring) effects6,7, 11-13. Somatic deterministic effects are proportional to a certain dose

and will therefore take place only if the dose is reached or exceeded (a threshold dose).

Somatic stochastic effects are not dose related and as such may or may not happen (no

threshold dose, there is a chance of them to happen). Therefore there are no distinct values

of doses under which these effects will not happen. Moreover, the severity of the tissue

damage caused by the radiation is not related to the dose to which the patient has been

exposed.

Genetic stochastic effects may involve mutations in DNA, for example, caused by ionizing

radiation. But again, there is no dose-effect relationship in this case (no threshold dose).

As dental imaging does not involve irradiation of the reproductive organs and the doses used

are very low, genetic stochastic and somatic deterministic effects are not of concern,

whereas somatic stochastic effects are the damaging effects of most concern. Therefore care

should be taken when numerous radiographs in young individuals are required, such as in

dento-alveolar trauma. As there is no threshold dose above or below which damage will or

will not, respectively, definitely occur, uncertainty remains when dealing will low dose

radiation, such as in dentistry. Although the risk of a fatal cancer developing from an

intraoral radiograph is only 1 in 20 million for a 20 year old, but 3 in a million for a person

younger than 10 years old (table 4), the so called “collateral” damage is not known.

Repeated intraoral radiographs could cause skin lesions or bloodvessel lesions for instance.

These are just two examples of the so called somatic stochastic effects. The frequency of

these effects to happen can never be estimated! The latter is also supported in a document

from the ICRP (02/276/05 – 5 June 2006)10 that was published on the internet: “Although


22

there are recognized exceptions, for the purposes of radiological protection, the Commission

judges that the weight of evidence on fundamental cellular processes coupled with dose-

response data supports the view that in the low dose range, under 100 mSv, it is scientifically

reasonable to assume that the increase in the incidence of cancer or hereditary effects will

rise in direct proportion to an increase in the absorbed dose in the relevant organs and

tissues”. Further in the document it is stated that the Commission will continue to assume

the so called linear non-threshold (LNT) hypothesis, namely that at doses below 100 mSv a

given increment in dose will produce a directly proportionate increment in the probability of

incurring cancer or hereditary effects attributable to radiation. On the other side, the

document also emphasizes on the fact that a radiation dose below 1 mSv will only mean a

marginal increase above the natural background radiation to the patient. As such they do

not require additional radiation protection measures. However, the age of the patient is not

specified nor is the frequency of exposure.

Patient absorbed dose depends on the nature of ionizing radiation that is being used, the

exposure settings used and the tissues that are being irradiated. The latter is a very

important factor, as some tissues are more radiosensitive than others, because of the fact

that they contain fast growing cells. Moreover, the younger the tissues are, the more

sensitive they are to ionizing radiation. Just as in calculating the risk to develop a fatal cancer

due to ionizing radiation, a weighting factor for age should be considered for effective dose.

Most reports on effective radiation dose give figures for an adult male or female person.

Children are not just “small” adults and therefore an attempt should be made to calculate

different effective radiation doses for children for all ages. The nature of the tissues plays a

role in this calculation, but also the thickness of the tissues and the position within the body


23

of certain radiosensitive organs in relation to the age of the child (e.g. the position of the

thyroid gland changes with age).

Children who suffered a dento-alveolar trauma are subjected to numerous dental

radiographs for diagnosis, follow-up and therapeutic reasons. The maxillary incisors are the

most often injured teeth, implying that if no beam aiming device (BAD) is used, the primary

radiation beam is easily aimed (65 to 30° vertical angle) at the thyroid gland area of the child

(see figure 1).

Depending upon the age of the patient, the patient’s intra-oral anatomy, or the type of

trauma (e.g. complicated crown fracture versus luxation of a tooth) the intraoral

radiographic techniques used in this region are often upper standard occlusals and bisecting

angle technique instead of parallel technique. The advantage of the latter is not only

geometric accuracy, but also the fact that the primary beam is not aimed at the thyroid

gland. For both other radiographic techniques, it is necessary to use a thyroid shield or

collar, but this is often forgotten by most dentists, or they do not appreciate its importance,

or the patient is too wriggly to keep the thyroid shield in place or there is no thyroid shield

or collar available.


24

Figure 1. Illustration of two vertical angulations of the central ray of the primary radiation

beam (blue arrow for upper standard occlusal, 65° and red arrow for a bisecting angle

technique, 30 to 45° angle)


25

CHAPTER 2 : Aims of this study

The first aim of this study was to evaluate existing literature over the past 10 years on

effective radiation dose in intra-oral radiographs in children, especially the dose absorbed by

the thyroid gland. The reason for choosing only literature of the past decade was merely a

matter of collecting the most recent data available on modern equipment (DC-machines and

E/F-type analogue film or digital detectors). The author considered it not useful to compare

values measured from and/or with outdated equipment or obtained by outdated methods.

The second aim was to obtain information about the mean number and type (geometric

technique) of intraoral radiographs taken for different kinds of dental traumata at the Ghent

University Outpatient Dental Hospital in children and adolescents (aged 1 to 18 years old)

and thirdly to assess retrospectively the theoretical effective dose to the thyroid gland

through PCXMC® calculations (Personal Computer X-ray dosimetry by Monte Carlo

estimation calculations). PCXMC® calculations were performed using the ICRP 1990

guidelines (PCXMC® version 1.5) as well as the ICRP 2005 guidelines (PCXMC® version 2.0).

It should be emphasized that until September 2005 the Ghent University Dental School used

D-speed film (always exposed at 60 kVp, 0.4 s and 10 mA) and that since E/F-speed is used

with different exposure parameters according to the anatomical area of interest and the

tissues that are under investigation (e.g. 60 kVp for periodontal bitewings and 70 kVp for

caries detection bitewings).


26

It is expected from these PCXMC® calculations that a confirmation will be obtained to the

following four null hypotheses regarding effective dose to the thyroid gland, obtained from

intra-oral radiography of the maxillary incisor region:

a. There is no significant difference in the effective dose to the thyroid gland between

the following two exposure settings a“60 kVp tube voltage, 0.4s exposure time ,10 mA

cathode current” and b“70 kVp tube voltage, 0.1 exposure time, 10 mA cathode

current”.

b. There is no significant difference in effective dose to the thyroid gland when different

X-ray beam angulations are used.

c. There is no significant difference in the effective dose to the thyroid gland between

individuals of different ages.

d. There is no significant difference in estimated effective dose to the thyroid gland

between the 2 PCXMC® versions.


27

CHAPTER 3 : Material and Methods

1. Literature search

A literature search was performed using PubMed® and Ovid® for articles published between

1998 and March 2008. The following key words were used: effective radiation dose,

children, p(a)ediatric, intra-oral radiography, dental, absorbed radiation dose, effective

organ dose and mathematical dose calculations. Articles from before 1998 were only

included if they were considered significantly important for this study.

Via Google® a world wide web (www)-search was performed. The latter was necessary as

some reports, such as those from the ICRP (International Commission on Radiation

Protection) for example, are better accessible in this manner. The same holds for local

guidelines and radiation dose assessment and calculation studies as for company contacts

(e.g. STUK® in Finland, who provide a software packet for effective dose calculations).

The author also choose to follow some conversations on Oradlist® ([email protected]),

a virtual platform on the internet where experts, manufacturers and practitioners share

information on clinical, but also radiation physics and radiation dose, issues in the field of

dental and maxillofacial radiology.

Books (English written only) were also used to verify radiation data and calculation methods.

2. Clinical data

To obtain an idea of the average number of radiographs taken in case of dento-alveolar

traumata, the author draw a random sample of 112 cases (between December 1992 and


28

January 2008) from the dental outpatient clinic of the Ghent University Hospital were

selected. The hard copy, hand written files were selected through the dental hospital’s

computerized agenda by using the search word ‘trauma’. A total of 63 hard copy files was

retained for the study. The other 49 cases could not be used because the hard copy file had

disappeared (in the patient’s possession, send to a private dentist or archived in the

Hospital) or it was incomplete (the type of trauma and radiograph(s) could not be assessed).

Interesting to note is that before October 2005 only D-speed film was used (exposure factors

for “all” radiographs were 0.4s at 60kV and 10mA, DC equipment and rectangular

collimation). Since October 2005 E/F-speed film is being used and exposure settings

(exposure time and kV) were adapted to the site under investigation (70kV, 0.12s exposure

time, 10mA, DC equipment and rectangular collimation). These modifications were

introduced by the author of the present study. It was first suggested by the dental school’s

staff to set exposures fixed at 60 kVp and 0.2 seconds exposure time, comparable to the

settings used in the past, for all intra-oral radiographs. No thyroid lead protection was ever

used within either of these periods!

3. Personal Computer X-ray Monte Carlo (PCXMC®) calculations for effective doses

estimates

Finally a retrospective theoretical calculation of effective dose in children, aged 1, 5, 10 and

15 versus an adult person (a 20 year old) was performed using the PCXMC® software

versions 1.5 and 2.0.


29

Calculations were made for 65, 45 and 30 degree vertical angulations for the region of the

maxillary central incisors. The reason for choosing these angulations was the fact that in the

results of the Ghent University Hospital population it became clear that a mixture of

angulations (upper standard occlusal to bisecting angles and parallel technique) was used to

visualize this anatomical region radiographically. The latter was due to a lack of policy and

guidelines. The author estimated these three angulations from the radiographs that were

retrieved from the patient files. Image quality assessment of the radiographs lay on the basis

for choosing these three angulations. Elongation or foreshortening of the image provided an

idea which angles were used. In order to keep the number of calculations within reasonable

limits, only 3 vertical angulations, as mentioned above, were finally selected.

Different exposure settings, as used in the Ghent University Dental Outpatient Clinic, were

entered into the software program; 70 kVp with 1 mAs, 70 kVp with 2 mAs, 60 kVp with 2

mAs and 60 kVp with 4 mAs. These parameters, beam angulation and exposure settings,

made it possible to compare the different situations and to provide an answer to the four

null hypotheses mentioned in the aims of the study (chapter 2).

4. Statistical analysis

The statistical analyses were all carried out with the MedCalc® statistical software

(Medcalc®, Frank Schoonjans; http://www.medcalc.be), which is developed especially for

medical researchers. The level of significance was set at a P value of 0.05.


30

CHAPTER 4 : Results of the literature search

The literature search resulted in several kinds of studies:

- radiation doses and their potential implications on general health

- measuring absorbed radiation dose in phantoms (human cadavers and

anthropomorphic phantoms)

- mathematical methods to calculate absorbed dose

- comparisons of different readings from different measuring equipment

- implication of age, type of tissues irradiated and type of equipment, in the

calculations

- conversion of absorbed radiation doses of panoramic radiography to intra-oral

radiography

- reports from different authority bodies

The mails on Oradlist® provided a view on how clinicians and university educators search for

practical solutions to keep the dose to the patient as low as possible in all kinds of

circumstances (e.g. endodontics where a high number of radiographs are taken sometimes

for the treatment of one tooth). Besides these issues, information about calculating the

radiation dose for the patient was obtained from different experts all over the world. At the

time of writing this paper, the most recent answer concerning the effective dose to a patient

for intra-oral radiography was that the practitioner should always try to use rectangular

collimation, fast films or receptors and that for the calculation of the effective dose, we have

to rely on linear extrapolation of doses calculated from other radiographic techniques or

situations (e.g. the effective dose for 6 peri-apicals in endodontics can be derived ‘roughly’


31

from the effective dose of a full mouth survey of peri-apicals) – ‘end quote’ Stuart White and

Sharon Brooks – (this correspondence can be found as addendum 1).

To be able to list the different factors that need to be taken into account to assess the

effective radiation dose in patients and children in particular, the following findings are

worth emphasizing.

1. Factors that influence the absorbed dose in intra-oral radiography

Kaeppler et al. (2007)14 investigated the factors that influence the absorbed dose in intra-

oral radiography. They clearly identify the problem of radiation beyond a film or detector in

the mouth. In case of analogue film, a thin lead foil is positioned behind the film within the

plastic package. It was found that adding two additional lead foils behind the film package

resulted in a 14% reduction of absorbed dose at 60 kV and 1.75 mAs. A metal film holder

reduced the absorbed dose to almost 28% at 60 kV and 1.75mAs. When using photo

stimulable phosphor storage plates (PPSP) or solid state detectors, such as charged coupled

devices (CCD) a lower mAs (0.84 mAs and 0.42 mAs respectively) can be used, which results

in a reduction of 52% and 77% respectively at 60 kV.

They calculated entrance (near the skin) and exit dose (behind the film) for different kV

settings, within a range of 60 to 90 kV and used an Alderson phantom head (Alderson

Research Laboratories). The doses were measured by means of thermoluminescent

dosemeters (TLDs) inside and outside of the phantom head. They calculated the effective

dose by using tissue weighting factors (ICRP 60 radiation and tissue weighting factors were

used) and adding the different calculations to obtain the total effective radiation dose for a


32

certain organ or part of the body. They implemented the skin (for both entrance and exiting

dose), bone marrow, thyroid gland, pituitary gland and salivary glands. It was emphasized

that it was necessary to work with rectangular collimators and to respect the parallel

technique in intra-oral radiography, in order to obtain substantial absorbed dose reductions,

like the ones they found. Moreover, the use of radiation sensitive detectors or films, the use

of DC equipment and using a low mAs product at reasonably low kV settings (60 to 70 kV)

was stressed to achieve lower absorbed radiation doses for the patient.

Svenson et al. (2004)15 mention the importance of collimation in the reduction of absorbed

radiation dose. They investigated the radiation dose to the thyroid gland for panoramic,

cephalometric and intra-oral radiographs, and used different collimators. This resulted in a

15% reduction of the absorbed radiation dose to the thyroid gland when smaller collimators

were used.

A study by Aragno et al. (2000)16 that assessed tooth enamel electron paramagnetic

resonance irradiation doses, a retrospective dosimetry technique used to measure an

individual’s accidental high energy radiation exposure, mentions the importance of implying

the age of the patient in assessing the absolute absorbed radiation dose from dental

radiography. It is emphasized that the relative weight of natural background radiation to

dental radiation is dependent on the patient’s age and the number of dental radiographs

taken over that period. It is suggested that the dental radiological radiation dose can be

calculated as the dose from a single exposure times the number of radiographs made during

a certain period of time.


33

2. Measurement of radiation dose in dental radiology

According to Helmrot and Carlsson (2005)17 the most commonly used dose parameters are

“entrance surface air kerma” (ESAK) for intra-oral radiography, while for panoramic

radiography, “dose width product” (DWP) is used. They suggest that “dose area product”

(DAP) should be used for all radiation dose calculations in dental radiography and for dose

reference levels (DRL). The DAP can be conversed into effective dose, by means of

conversion factors. The latter are mostly derived from so called Monte Carlo generated

conversion factors. The name Monte Carlo was chosen because of the link to casinos and the

calculation of chances or risks of certain things to happen. According to Williams and

Montgomery18, for panoramic radiography a conversion factor of 0.06 mSv per Gy cm2 is

needed. Carlsson et al.19 calculated conversion factors for intra-oral radiography of 0.06 to

0.07 mSv per Gy cm2 for a tube voltage of 60 to 70 kV. The latter study dates back 24 years,

nevertheless it contains still substantial information.

Gray et al. (2005)20 report that the American Association of Physicists in Medicine require

reference values for computed tomography, fluoroscopy and dental radiography. The use of

these guidelines is necessary to detect equipment that is not working correctly or not being

manipulated correctly. Moreover it can also be used to compare patient radiation doses

between different centers or practices. They also emphasize that reference values do not

provide a threshold for what is to be considered acceptable or unacceptable practice of

radiology.

Kuroyanagi et al. (1998)21 studied the distribution of scattered radiation during intra-oral

radiography with the patient (a phantom) in a supine position. They measured the radiation

doses with ionization chambers, which were placed at several distances and under certain


34

angles. They even measured till 30 cm below the occlusal plane. They found the lowest

doses at 30 cm below the occlusal plane and behind the patient (180 till 135° angles).

Stenström et al. (1986)22 already mention that rectangular collimation and the use of

sensitive films play an important role in the attempt to reduce the absorbed radiation dose.

They calculated that the difference in radiation between D-speed film and E-speed film for a

set of 20 intra-oral radiographs with a tube voltage of 65 kV, expressed as environmental

radiation is 14 days and 9 days respectively.

Rassow (1998)23 published a paper on the calculation of organ doses, in which it is stated

that the most, but unfortunately impossible and unethical, appropriate method to

determine the effective dose in a particular organ is to place a detector (e.g. TLD) in the

organ itself and to expose the patient as if one would do for a certain radiological procedure.

However, the dose area product (DAP) remains the most comprehensive way to illustrate

absorbed radiation dose. DAP is defined as the product of the entrance dose at a reference

distance and the field size. DAP is independent of focus-to skin distance, because of the

inverse square law (the intensity of the radiation decreases proportionately with the value of

the distance from the radiation source squared). This paper also refers to a study executed

in 1992 by Le Heron, in which conversion factors are calculated to estimate the effective

dose from DAP measurements. Calculations for 22 different X-ray examinations are

presented, but for the purposes of the present paper, the figures for the skull are

interesting, especially those for 60 and 70 kVp and filtration with 1.5 and 2.0 mm aluminium.

Differentiation is further made to posterior anterior, anterior posterior and lateral

projections. In table 7 the conversion factors for the skull radiographs are presented.


35

Table 7. Conversion coefficients to give effective dose (mSv) from DAP (Gy cm²) for anterior

posterior (AP), posterior anterior (PA) and lateral radiographic projections for the skull at 60

and 70 kVp with 1.5 and 2.0 mm aluminium filtration respectively, according to Le Heron

199225.

kVp Al

filtration

AP

projection

conversion

factor

DAP for

AP

projection

(mSv/Gy cm²)

PA

projection

conversion

factor

DAP for

PA

projection

(mSv/Gy cm²)

Lateral

projection

conversion

factor

DAP for

lateral

projection

(mSv/Gy cm²)

60 1.5 mm 0.017 0.04 0.012 0.025 0.016 0.03

2.0 mm 0.019 0.04 0.014 0.025 0.019 0.03

70 1.5 mm 0.022 0.04 0.016 0.025 0.021 0.03

2.0 mm 0.025 0.04 0.018 0.025 0.024 0.03

A study conducted in Luxembourg and published in 2006 by Shannoun et al.25 estimated the

annual collective dose of its population between 1994 and 2002. The annual collective dose

increased by 24.5% between 1994 to 2002, which was largely attributed to the impact of

computed tomography. They emphasize that more should be done to limit the patient

absorbed dose and that perhaps an individual electronic X-ray passport should be introduced

to monitor an individual’s exposures. They stress that this passport should not include

exposure from dental radiation procedures.

Regulla and Eder (2005)1 estimated the mean radiation exposure from medical imaging in

Europe per person per year. They show a table with figures from 16 European and 4

overseas countries, which tabulates the mean annual effective dose per head of the

population for each country. For Belgium this is 1.78 mSv/person/year and for the UK this is

only 0.33 mSv/person/year. The figures in the table do not include dental radiographic


36

exposures, except for Germany’s and the UK’s, 2.0 mSv/person/year and 0.33

mSv/person/year respectively. These authors emphasize on the fact that the mean effective

dose per person per year no doubt would be higher for the other countries if dental

radiographic exposures were included in the calculations. The latter because of the high

number of dental radiographs taken per person per year and not because of the high

effective dose to the patient. The total of dental radiographic examinations is estimated to

be about 20% of all medical imaging. They also stress that each country appears to have its

own criteria to calculate the population’s effective radiation dose from medical exposures

and that therefore comparisons should be interpreted with care. It is also mentioned that

the organs within the radiation beam are exposed to significantly higher doses, which should

be taken into account when calculating effective dose. This is especially the case for the skin

and this can reach a factor ≥ 10.

They also stress the fact that retakes are in most cases not registered and as such not

calculated into the total to estimate the effective dose per head. Eder et al. (2001)26

estimated that for Germany the number of retakes would mean an increase in annual

effective dose per person of 0.15 mSv.

McCollough and Schueller (2000)8 stress that estimates of effective dose can be used as a

relative measure of stochastic radiation detriment.


37

3. Absorbed radiation dose of intra-oral radiography in children

Regulla and Eder (2005)1 mention in their discussion on the need for harmonized criteria for

data collection that the paediatric radiological exposures should not be forgotten. They

would like to include new and early born children. Age of the patient should be considered

as well as sex, genetic predisposition and immune status. The risk factor to develop a lethal

cancer is age dependent and can be as great as 10 when comparing children with elderly.

Stratakis et al. (2005)27 focused on and assessed the organ and effective radiation dose in

paediatric skull radiographs, by using anthropomorphic phantoms and Monte Carlo

calculations. As the diagnostic reference levels, as specified by authorized bodies and the

European Community, indicate a high entrance surface dose for skull examinations, the

contribution of this kind of radiographs to the child’s collective dose may be substantial.

They stress the need for an age specific database on effective radiation doses for children,

instead of the ones suggested by the National Radiological Protection Board (NRPB), the PC-

based Monte Carlo program for calculating patient doses in medical X-ray examinations

(PCXMC – Tapiovaara et al., 1997)28 and by the ADA in their Centre for Devices and

Radiological Health (CDRH), with age increments of 5 years. Stratakis et al.27 calculated the

doses to the thyroid gland and the bone marrow in children between 0 and 6 and in children

9 and 14 years old for posterior anterior, anterior posterior and lateral skull projections.

Table 8 shows the effective radiation dose for 60 and 70 kV at 3 mm aluminium filtration to

the bone marrow and the thyroid. Filtration below 3 mm aluminium was not measured in

this study, nor was the effect of intra-oral radiography on these measurements.

It was concluded that all effective doses show an inverse relation correlation with age and

moreover, because of the distinct differences in effective doses for every age, these authors


38

emphasize on the importance of implementing age in the calculation. The effective dose is

also affected by the kVp, the filtration of the beam and the radiographic projection. They

conclude that the dose to the thyroid gland is not to be neglected as it concerns a

radiosensitive organ, as is the red bone marrow at this age. Moreover, about one third of the

red bone marrow is located in or near the cranium in the first years of life. Their final

conclusion is that the differences in effective dose for a newborn and a 6 year old are

significant, but that the effective dose range for a 9 and a 14 year old can represent the age

group 7 to 17 year olds, as the figures in their study are not differing more than 10% with

those of the NRPB for a 10 and a 15 year old.

Table 8. Effective dose to red bone marrow (E RB Marrow) and thyroid gland (E Thyroid) in µSv for

a 1 mGy entrance surface dose for posterior anterior (PA), anterior posterior (AP) and lateral

(LAT) skull projections (60 and 70 kVp with 3 mm aluminium filtration) in children aged 0 to

6, 9 and 14 years. (source: Stratakis et al., 200527)

Projection Age (yrs)

60 kVp 70 kVp

PA skull

(E RB Marrow) µSv

(E Thyroid) µSv (E RB Marrow) µSv (E Thyroid) µSv

0 73 26 97 32

1 41 12 53 17

2 25 10 41 12

3 23 8 37 10

4 17 7 26 11

5 14 6 17 10

6 10 6 16 9

9 10 5 19 6

14 11 5 14 5

AP skull

0 106 41 172 48

1 37 23 66 29

2 27 18 46 24

3 21 15 41 21


39

4 19 16 30 17

5 17 15 19 18

6 16 11 19 16

9 15 12 18 15

14 15 10 18 13

LAT skull

0 81 35 117 42

1 50 20 65 24

2 30 14 44 19

3 28 13 41 18

4 21 10 35 15

5 17 10 18 14

6 15 9 16 13

9 15 9 16 13

14 14 8 16 13

Looe et al., 20065, mention the lack of European wide diagnostic reference levels (DRLs) for

dental radiological procedures. They were especially interested in the radiation exposure to

children in intra-oral radiography. They first measured the dose area products (DAP) of the

equipment used (52 units: 4 operating at 50 kV, 6 at 60 kV, 30 at 65 kV and 12 units at 70 kV

or with adjustable kV between 60 and 70 – 32 X-ray units had a child exposure setting) in the

study to calculate the different intra-oral radiographic radiation doses: peri-apical, bitewing

and occlusal radiographs. They emphasized on the fact that when not using the child

exposure settings, most of the DAP values resulted in a 50% “overdose”. The latter was

especially true for maxillary incisor radiographs, but not for maxillary occlusals. However, the

highest DAP values were measured for occlusal radiographs, and in particular for maxillary

occlusals. The measured DAP values are shown in table 9. As the current interest is in the

peri-apicals and occlusals of maxillary incisors, these figures are highlighted in grey.


40

Table 9. Third quartiles and means of the DAP values (mGy cm²) for only child exposure

settings (CES) and adult exposure settings (AES) for 12 intra-oral radiographic exposures.

(source: Looe et al. 20065)

Radiopgraphic

examination

Area of

interest

3rd quartile

DAP value

CES

Mean DAP

value CES

3rd quartile

DAP value

AES

Mean DAP

value AES

periapicals in

the maxilla

molars 40.9 29.7 48.8 39.1

premolars 27.7 19.7 37.6 27.1

canines 23.6 18.3 33.6 23.6

incisors 22.0* 17.1** 32.0* 24.3**

periapicals in

the mandible

molars 27.8 19.9 35.0 25.9

premolars 18.9 14.6 24.4 19.8

canines 18.9 14.6 24.4 19.6

incisors 14.4* 12.0** 20.6* 18.1**

bitewings anterior 39.8 28.0 41.6 29.1

posterior 41.7 29.9 41.9 30.4

occlusals maxilla 56.9 51.9 56.9 47.8

mandible 44.2 40.8 44.2 37.1

*between CES and AES DAP values there is a 50% difference, with CES being the lowest

**between CES and AES DAP values there is a 50% difference, with CES being the lowest

4. Absorbed radiation dose in young patients

A study carried out by Rush and Thompson in 200729, measured the radiation absorbed dose

by the thyroid gland, for peri-apical radiographs in the maxilla and mandible. Radiographs

were taken either with the paralleling technique or the bisecting angle technique. A third

and fourth variable were included, namely round versus rectangular collimation and the use

of a thyroid shield. It became clear that for the maxilla, the highest absorbed doses were


41

found for the premolars and incisors, especially when the bisecting angle technique was

used. Their overall conclusion was that by using a rectangular collimator and applying the

paralleling projection technique the thyroid gland was subjected to a significant lower

radiation dose. The thyroid dose was even further reduced when a thyroid shield was used

to cover the thyroid gland. They used, however, not a Rando® phantom, as is usual in

dosimetry studies, but a DXTTR phantom head instead (Rinn Corporation, Elgin, IL, USA), as is

used to teach intra-oral radiography (figure 2). The latter could imply inaccurate

measurements as the material, the phantom is made of, may attenuate and scatter the X-

rays differently than in an anthropomorphic phantom, which can be filled with

thermoluminescent dosemeters.

Figure 2. The dental X-ray trainer phantom, DXTTR® by Rinn Corporation, Elgin, IL, USA.

Hujoel et al., 20083, investigated the effective dose to the thyroid gland in patients under

orthodontic treatment. As most of these patients are children and adolescents, the

comparison with adults is not a correct one when it comes to organ dose calculations. The

latter is due to tissue volume differences, differences in organ location and differences in red


42

bone marrow fraction in the skull. Especially the thyroid gland needs attention in these

calculations, as this gland in a 6 year old is positioned 2 to 3 cm closer to the primary beam

than in a 16 year old. In figure 3 a schematic positioning is shown of the relative position of

the thyroid gland to the chin in a child and an adult. It is obvious that the thyroid gland in a

child is positioned higher up the neck than it is in an adult, where it is closer to the sternum.

Besides the thyroid gland, the portion of red bone marrow in the skull is much different in a

6 year old or an adult. Therefore calculating effective organ doses for children by just

extrapolating figures from adults, will result in erroneous conclusions.

Figure 3. Illustration of the relative position of the thyroid gland in a child (left) and an adult

(right) with respect to the maxillary incisors.

Concerning the thyroid gland, they estimated that the distance of the thyroid gland to the

primary beam increased by 0.9 mm for every year of chronological age from 6 to 14 years

and by 0.2 mm for every chronological age from 15 to 20 years. These estimates were

considered necessary as the position of the thyroid gland changes through childhood and

puberty. They also mention that compared to a 20 year old, the effective radiation dose


43

from extra-oral radiography to the thyroid gland, increased by 0.4% for a 19 year old, 2% for

a 15 year old and 18.6% for a 6 year old.

5. Mathematical models used to assess absorbed radiation dose

Kramer et al. (2003)9 used a male adult voxel phantom (MAX) to assess absorbed radiation

doses through Monte Carlo calculations. This phantom equals a male with a height of 175.3

cm and a weight of 74.6 kg, in which the absorbed radiation dose to 23 different organs can

be assessed. This phantom is an updated version of a previously used version, called the

Medical Internal Radiation Dose Committee pamphlet number 5 (MIRD5 phantom). A voxel

model is an exact replica of a real human body, whereas a real mathematical model is not. In

the latter the body and organs are considered spherical, elliptical, cylindrical or cone shaped,

for purposes of mathematical calculations and extrapolations from adults to children, for

instance. A voxel model, such as MAX, is a real three dimensional phantom model. MAX

allows a very accurate measurement of the effective doses, by using EGS4 Monte Carlo

codes (Electron Gamma Shower version 4 program). The above MAX phantom and EGS4

Monte Carlo calculations on it have been shown to be accurate for external photon

irradiation compared to the ICRP, so called, reference man (Vieira et al., 2004)30.


44

CHAPTER 5: Results of the clinical data

Clinical data from the Ghent University Outpatient Dental Hospital

From the 63 dento-alveolar trauma cases, the descriptive statistics such as the patient’s age

at the first and final visit, the total number of radiographs and the mean number of

radiographs per appointment are summarized in table 10.

Table 10. Descriptive statistics concerning age at first and final appointment and total

number of radiographs (including retakes) and mean number of radiographs taken per

appointment.

Parameter Mean +/- SD Median 2.5th percentile 97.5th percentile

Age at first visit 8.4 +/- 3.9 year 8.5 year 1.5 year 15.5 year

Age at final visit 10.1 +/- 4.5 year 10.5 year 1.5 year 18.0 year

Total number of

radiographs

7.7 +/- 6.0 6.0 1.0 22.9

Mean number of

radiographs per

appointment

1.4 +/- 0.8 1.0 0.5 3.9

The types of trauma involved were luxation, crownfracture (enamel and dentine, with or

without pulp involvement), enamel fracture only, intrusion, avulsion, intrusion and avulsion,

extrusion, intrusion and extrusion, and uncertain or untraceable was scored if in the file no

discrete data could be found.


45

In table 11 the prevalence of the recorded dental traumata is shown, for children under the

age of 5 and over the age of 5.

Table 11. Prevalence (percentage) of the dental traumata according to age.

luxation crown

fracture

enamel

fracture

avulsion intrusion extrusion abscess extrusion

and

intrusion

not

traceable

<5 y

old

66.7% 0% 0% 0% 20.0% 6.7% 0% 0% 6.7%

>5 y

old

14.6% 54.2% 8.3% 8.3% 4.2% 0% 4.2% 2.1% 4.2%

The geometry used to make the radiographs was summarized as parallel technique,

bisecting angle technique, maxillary occlusal and miscellaneous if the radiographs in the file

showed different angles of radiographic exposure of the involved teeth. The results showed

that under the age of 5, most of the radiographs were made using the occlusal technique

(86.7%), while over the age of 5, the parallel technique and a mix of geometric techniques

was used most often (28.3% and 26.1% respectively). In table 12 the percentages of the

different geometric techniques used in these age categories are shown.

Table 12. The different geometric techniques used to make radiographs in children under

and over the age of 5, who suffered a dental trauma.

parallel

technique

bisecting angle

technique

occlusal

technique

miscellaneous not traceable

<5 y old 0% 0% 86.7% 6.7% 6.7%

>5 y old 28.3% 17.4% 6.5% 26.1% 21.7%


46

Chi square test results are shown in table 13 for the frequency of geometric technique used

versus the type of dental trauma, regardless of age.

Table 13. Chi square test results for the frequency of the geometric technique used versus

the type of dental trauma, regardless of age.

Codes X geometry

Codes Y type of trauma

Codes X

Codes Y parallel bisecting

angle

occlusal miscellaneous not

traceable

Luxation 1 2 9 4 1 17 (27.9%)

Crown fracture 4 5 1 9 5 24 (39.3%)

Enamel fracture 2 1 0 0 1 4 ( 6.6%)

Avulsion 2 0 1 0 1 4 ( 6.6%)

Intrusion 1 0 4 0 0 5 ( 8.2%)

Extrusion 0 0 1 0 0 1 ( 1.6%)

Abscess 2 0 0 0 0 2 ( 3.3%)

Extrusion and

intrusion

1 0 0 0 0 1 ( 1.6%)

Not traceable 0 0 0 0 3 3 ( 4.9%)

13

(21.3%)

8

(13.1%)

16

(26.2%)

13

(21.3%)

11

(18.0%)

61

Chi-square 59.502

DF 32

Significance level P = 0.0022

Contingency coefficient 0.703

Frequency chart


47

Figure 4. The total number of radiographs in relation with the type of trauma (1 = luxation; 2 = crown fracture; 3 = enamel fracture; 4 = avulsion; 5 = intrusion; 6 = extrusion; 7 = abscess; 8 = extrusion and intrusion; 9 = not traceable)

Means 20

15

10

5

0

type of trauma

1 2 3 4 5 6 7 8 9

tota

l num

ber o

f ra

diog

raph

s

From the above, it can be derived that the parallel technique is not the most frequently used

geometric technique at the Ghent University Dental School in case of dental trauma.

Occlusal radiography is the most frequently used technique (26.2%), closely followed by

miscellaneous geometric technique and parallel technique, who both each represent 21.3%.

In figure 4 a frequency bar chart of the total number of radiographs per type of trauma is

shown. From this graph it is clear that a complete treatment of a crown fracture, an avulsion

and a combined trauma (intrusion with extrusion) at the Ghent University Hospital require

about ten radiographs. However, a case with an abscess or fistula requires about twice as

many. For all other traumata about 4 radiographs seem to suffice.


48

Figure 5 is an illustration of some of the radiographs taken at the Ghent University Dental

Outpatient Hospital during the period 1993 to 2007. It is obvious from these images that

there is no consistency in the way the radiographs were taken. It is from radiographs as

these that the author had to estimate the projection angle and concluded to select three

vertical X-ray beam angulations, to be further used in the theoretical estimations. Therefore

it is interesting and justifiable to conduct a study in which the effective dose to the patient’s

thyroid gland is estimated.


49

Figure 5. Illustrations of peri apical radiographs taken at the Ghent University Dental Outpatient Hospital of children with a dento-alveolar trauma. Except for the last one,

all images are paired, to illustrate the inconsistency of the geometry used.


50

CHAPTER 6: Results of the PCXMC® calculations based on the clinical

data

Theoretical approach of the effective dose of the Ghent University Hospital Dental

Outpatient paediatric trauma patients by means of PCXMC® calculation

Because it was clear from the above that most of the time miscellaneous X-ray beam

angulations were used and that after September 2005 a switch was made to more sensitive

films, the PCXMC® software was programmed to calculate the effective dose, so that an idea

could be obtained about the total effective dose and the absorbed radiation dose by the

thyroid gland, the salivary glands (PCXMC® version 2.0 calculations only), the oesophagus,

the bone surface and the skin for the following exposure settings:

- Rectangular collimation of 3 by 4 cm

- 60 kVp and 0.4 seconds exposure time and 10 mA




- For all the above, the X-ray tube was theoretically aimed at the central maxillary

incisors at three vertical angles of 30°, 45° and 65° respectively.

In figure 6 a screenshot is shown of a PCXMC® calculation page. First the patient’s age has to

be selected, then, the kVp which will be used, the width and height of the X-ray beam

(collimation of 3 by 4 cm), the position and angulation of the X-ray beam and the skin-focus

distance can be put in. The latter was set at 22 cm. The reason for also selecting the second

and third exposure settings, was that in the Ghent University Dental School the dental staff


51

Figure 7. Illustration of the Ghent University Dental School phantom radiographs for intra-oral radiography

The left figure indicates kVp (6 for 60 and 7 for 70) , the right figure indicates exposure time (1 for 100ms, 2 for 200ms and 4 for 400ms) and the letters D,E and F stand for the film speed that was used.

in September 2005 first suggested only to decrease the exposure time by 50% and not to

alter the X-ray tube voltage from 60 to 70 kVp.

Figure 6. Screenshot of the calculation page of the PCXMC® version 1.5 program.


52

Figure 8. Phantom developed by the Ghent University Dental School for evaluation of intra-oral radiography and X-ray machine exposure settings checking.

In figure 7 it becomes clear that if the wrong exposure settings would have been chosen at

that time (September 2005), the quality of the clinical images would have been of

“rejectable” quality. The Ghent University Dental School has developed its own custom

phantom (figure 8) to test the X-ray machine’s output, so exposure settings can be adjusted

if necessary. The latter is of utmost importance when a technical problem has occurred and

has been taken care of. Before an X-ray machine can be put back into service, a check is

done with this phantom. The phantom consists of a plastic carrier, in which a film package

can be held, and on top of which an extracted human maxillary molar and an aluminium

stepwedge of 10 steps is fixed. On the side of the plastic plate, two metal bars are mounted

in which figures are milled. The latter is important to be able to leave a mark on the film, so

one can always decipher the exposure settings (e.g. 64 stands for 60 kVp and 400

milliseconds exposure time). In figure 7 it can be observed that the 10 steps of the


53

aluminium stepwedge and the details of the dental pulp of the maxillary molar can be best

evaluated on D-speed film at 60 kVp and 0.2 seconds exposure time and on E/F-speed film at

70 kVp and 0.1 seconds exposure time. The latter is worth mentioning as in the PCXMC®

calculations these exposure settings are included.

Table 14. The effective doses (µSv) to the thyroid gland, the oesophagus, the skeleton and

the skin for 4 different exposure settings and 3 different vertical X-ray tube angulations in

four different ages, as calculated by the PCXMC® (version 1.5) software.

age angle kVp mAs E skeleton E thyroid E oesophagus E skin E total

1

30

60

4

53 307 36 29 22

45 57 343 28 34 24

65 75 137 9 52 14

5

30 59 23 7 14 4

45 58 169 11 17 11

65 58 77 4 29 7

10

30 38 24 7 9 3

45 40 49 6 11 4

65 40 51 2 18 4

15

30 25 15 4 6 2

45 25 47 4 8 3

65 21 47 1 12 3

20

30 20 25 4 5 2

45 19 69 3 6 4

65 16 38 1 10 3

1

30

2

27 154 18 15 11

45 29 172 14 17 12

65 37 68 4 26 7

5

30 30 11 4 7 2

45 29 85 5 9 6

65 29 38 2 14 4

10

30 19 12 3 5 1

45 20 25 3 5 2

65 20 25 1 9 2

15

30 13 8 2 3 1

45 13 23 2 4 2

65 11 24 1 6 2

20

30 10 12 2 3 1

45 10 35 1 3 2


54

65 8 19 1 5 1

1

30

70

2

39 239 32 20 17

45 41 273 25 23 20

65 54 115 8 35 11

5

30 43 20 7 9 3

45 42 145 10 12 10

65 43 69 4 19 6

10

30 28 21 6 6 3

45 29 44 6 7 4

65 30 48 2 12 4

15

30 19 14 4 4 2

45 19 43 4 5 3

65 17 46 2 8 3

20

30 15 23 4 4 2

45 15 64 3 4 4

65 13 37 1 7 2

1

30

1

20 120 16 10 9

45 21 136 13 11 10

65 27 57 4 18 6

5

30 22 10 4 5 2

45 21 72 5 6 5

65 21 34 2 10 3

10

30 14 11 3 3 1

45 15 22 3 4 2

65 15 24 1 6 2

15

30 10 7 2 2 1

45 10 21 2 3 2

65 8 23 1 4 2

20

30 8 11 2 2 1

45 7 32 1 2 2

65 6 19 1 3 1

In table 14 the calculated effective doses in micro Sievert (µSv) are presented for the

different exposure settings and angulations per age. The four different ages that were

calculated are set by the PCXMC® software. No ages in between can be chosen, but the ones

used can serve as a guideline for estimating the differences in effective dose to the tissues

between the different exposure settings and the different vertical angulations used.


55

To increase the interpretation of the figures in table 14, the figures for the effective dose to

the thyroid and the total or whole body effective dose are visualized as box-and-whisker

plots in figures 9 and 10 respectively.

Figure 9. Box-and-whisker plots of the effective dose to the thyroid gland (µSv) for four

different exposure settings (70 kVp and 1 mAs, 70 kVp and 2 mAs, 60 kVp and 2 mAs and 60

kVp and 4 mAs) as a function of age. Calculations performed with PCXMC® version 1.5.

From the graphs in figures 9 and 10, it can be observed that the dose to the thyroid gland is

substantially higher for a 1 year old than for an 10 or 20 year old. It also appears that from


56

the age of 10, there is no substantial absorbed dose difference. This is true for every

exposure setting included in the present study.

Statistical analysis to verify differences between ages, beam angulations and exposure

settings for effective dose to the thyroid gland were conducted by means of the MedCalc®

statistical software (Medcalc®, Frank Schoonjans ; http://www.medcalc.be). The level of

significance was set at a P value of 0.05.

Figure 10. Box-and-whisker plots of the total effective dose (µSv) for four different exposure

settings (70 kVp and 1 mAs, 70 kVp and 2 mAs, 60 kVp and 2 mAs and 60 kVp and 4 mAs) as

a function of age. Calculations performed with PCXMC® version 1.5 software.

http://www.medcalc.be/�


57

Further statistical analysis will focus on the influence of the implemented variables on the

total effective dose and on the absorbed dose by the thyroid gland, the salivary glands and

the oesophagus.

A. Effective dose to the thyroid gland as a function of age

ANOVA analysis showed a significant difference for the effective dose to the thyroid gland

between the age groups. Subsequent Student T-tests were executed and the results of these

are shown in table 15.

Table 15. Results of the Student T-tests for effective dose to the thyroid gland (E thyroid) as

a function of age, irrespective of the exposure settings used in this study. (NS stand for not

significant or P>0.05)

E thyroid

Student T-

test results

1 year old 5 year old 10 year old 15 year old 20 year old

1 year old P=0.0012 P<0.0001 P<0.0001 P<0.0001

5 year old P=0.043 P=0.029 NS

10 year old NS NS

15 year old NS

20 year old

Compared to a one year old child, the differences in effective dose, for subjects aged 5, 10,

15 or 20, to the thyroid gland are very significant. The effective dose to the thyroid gland


58

decreases with increasing age. Between a five year old and a 10 or 15 year old the

differences are also significant, with obviously the 5 year old’s thyroid gland receiving the

highest dose.

Because the Ghent University Dental School changed in September 2005 to E/F-speed film

and obviously started to use different exposure parameters, the calculations in table 15

were repeated for 4 different exposure settings (see also table 14). Table 16b shows the

results of the Student T-tests for the effective dose to the thyroid gland as a function of age,

for 4 different exposure settings, expressed as the product of kVp and mAs (table 16a). The

latter calculations should be interpreted as follows;

Table 16a. The four different exposure settings used for the PCXMC® calculations

From table 16b it becomes clear that, irrespective of the exposure settings used, there was

only a significant difference in effective dose to the thyroid when 10, 15 and 20 year old

individuals were compared to a 1 year old. There is no significant difference in effective dose

to the thyroid between a 1 year old and a 5 year old.

A Student T-test was performed for the effective dose to the thyroid gland as a function of

age, for the exposure settings used before and after September 2005 (60 kVp and 0,4

seconds exposure time versus 70 kVp and 0,1 seconds exposure time) at the Ghent

1. 60 kVp and 0.4 seconds exposure time and 10 mA ► kVp*mAs = 240 2. 60 kVp and 0.2 seconds exposure time and 10 mA ► kVp*mAs = 120

3. 70 kVp and 0.2 seconds exposure time and 10 mA ► kVp*mAs = 140

4. 70 kVp and 0.1 seconds exposure time and 10 mA ► kVp*mAs = 70


59

University Dental School. The results showed no significant difference in effective dose to

the thyroid gland whatsoever (P>0.05).

Table 16b. Results of the Student T-test for the effective dose to the thyroid gland (E

thyroid) as a function of age, under 4 different exposure settings, expressed as the product

of kVp and mAs (kVp*mAs). Calculations performed with PCXMC® version 1.5 software

program. (NS stands for not significant)

Age

groups

kVp*mAs 1 year old 5 year old 10 year old 15 year old 20 year old

1 year old 240 NS P=0.026 P=0.025 P=0.028

5 year old NS NS NS

10 year old NS NS

15 year old NS

20 year old

1 year old 120 NS P=0.027 P=0.025 P=0.029

5 year old NS NS NS

10 year old NS NS

15 year old NS

20 year old

1 year old 140 NS P=0.025 P=0.024 P=0.028

5 year old NS NS NS

10 year old NS NS

15 year old NS

20 year old

1 year old 70 NS P=0.025 P=0.024 P=0.028

5 year old NS NS NS

10 year old NS NS

15 year old NS

20 year old


60

B. Effective dose to the thyroid gland as a function of X-ray beam angulation

Student T-test only showed a significant higher, though borderline (P=0.045), effective dose

to the thyroid gland when a 45° vertical X-ray beam angle was compared to a 65° angle.

When also taking the exposure settings into account (table 16a) no significant differences

were found whatsoever for effective dose to the thyroid. Figure 11 illustrates the latter

findings.

Figure 11. Box-and-whisker plots of the effective dose to the thyroid gland as a function of X-

ray beam angulation and exposure settings, as used in this study.


61

However, when comparing the effective dose to the thyroid gland with respect to age and

central X-ray beam angulation, several significant differences were observed (table 17). The

highest effective dose to the thyroid was always associated with the youngest age. For

purposes of review, table 17 doesn’t show the effective doses, but the P-values obtained

from the statistical analysis. A table containing the different effective doses would not be

surveyable.

For a vertical projection angle of 30°, significantly different thyroid gland doses were found

only when comparing a one year old with older subjects. The younger the individual, the

higher the effective dose.

For a vertical projection angle of 45° and 65°, the difference in effective dose to the thyroid

gland was only significant between a 1 year old and individuals of at least 10 years old.

Again, the effective dose was higher in a younger individual.

For a vertical projection angle of 45°, it was observed that the effective dose to the thyroid

gland in a 5 year old was significantly higher when compared to older subjects.

Comparisons between the effective doses to the thyroid gland as a function of X-ray beam

angulations in individuals of at least 10 years old, did not show any significant differences.


62

Table 17. Student T-test results (P-values) for the absorbed dose by the thyroid gland as a

function of age and central X-ray beam angulation. (NS stands for no significant difference)

Age

(angle)

5 (30) 5

(45)

5

(65)

10

(30)

10

(45)

10

(65)

15

(30)

15

(45)

15

(65)

20

(30)

20

(45)

20

(65)

1 (30) 0.0043 0.0044 0.0037 0.0045

1 (45) NS 0.0063 0.0061 0.0095

1 (65) NS 0.0306 0.0259 0.0156

5 (30) NS NS NS

5 (45) 0.0144 0.0133 0.0363

5 (65) NS NS NS

10 (30) NS NS

10 (45) NS NS

10 (65) NS NS

15 (30) NS

15 (45) NS

15 (65) NS

C. Comparison of the PCXMC® version 1.5 with PCXMC® version 2.0 calculations

As the latest ICRP 2005 guidelines included a weighting factor for the salivary glands, it may

be interesting to compare the data for effective dose obtained from the two different

versions of the PCXMC® software. The PCXMC® version 2.0 includes the latest ICRP 2005

guidelines. The question, however, remains what the impact is on the estimates of the

effective doses to the thyroid gland, for instance.

Would working with the PCXMC version 2.0 give significantly different estimates for the

effective dose to the thyroid gland, compared to the estimated figures with the PCXMC®

version 1.5?


63

Box-and-whisker 250

200

150

100

50

0

age

E' S

al g

land

s

1 5 10 15 20

In figure 12 it can be seen that, irrespective of the four different exposure settings and the 3

angulations (30°, 45° and 65°) as used in this study, the effective dose to the salivary glands

also decreases with age, as did the doses to the thyroid glands.

Figure 12. Box-and-whisker plot for the effective dose to the salivary glands as a function of

age, according to the PCXMC® version 2.0 calculations.

In table 18 the statistical significant differences between the ages, regarding the effective

dose to the salivary glands, estimated with the PCXMC® 2.0 software, are shown. This table

is in fact a “translation” of the “apparent” differences in absorbed dose by the salivary

glands, shown in figure 12. The differences in effective dose to the salivary glands between a

5 and a 10 year old, a 10 and a 15 year old and between a 15 and a 20 year old were not

significant (P > 0.05).


64

Table 18. Student T-test results (P-values) of the effective dose estimates to the salivary

glands between the different ages, according to the PCXMC version 2.0 software calculations

(NS stands for no significant difference).

1 year old 5 year old 10 year old 15 year old Adult

1 year old P = 0.0191 P = 0.0016 P = 0.0001 P < 0.0001

5 year old NS P = 0.0059 P = 0.0004

10 year old NS P = 0.0044

15 year old NS

adult

As PCXMC® version 1.5 was based on the ICRP 1990 guidelines, a comparison between the

two programs, with respect to effective dose to the salivary glands, is not possible. However,

for the other effective organ doses, it is. The differences between the calculations from the

PCXMC® version 1.5 and version 2.0 are shown in the next tables (19 to 26).

Table 19. Student T-test results (P-values) of the comparison of the 2 PCXMC® versions

regarding effective dose to the thyroid gland with respect to the age groups.(NS stands for

no significant difference)

Version 1.5 vs.

version 2.0

1 year old 5 year old 10 year old 15 year old adult

1 year old NS

5 year old NS

10 year old NS

15 year old P = 0.0003

adult P = 0.0002


65

Box-and-whisker 600

500

400

300

200

100

0

age = 1E thyroid E' Thyroid

Box-and-whisker 70

60

50

40

30

20

10

0

age = 20E thyroid E' Thyroid

From table 19 it can be derived that there was only a significant difference in the estimated

value of the effective dose to the thyroid gland for persons of at least 15 years old. The

estimated value of the PCXMC® version 2.0 was significantly lower than the PCXMC® version

1.5 calculated value.

The latter is visually illustrated in figure 13, where two box-and-whisker plots are shown, for

a 1 year old (no significant difference between the estimates by the 2 software versions of

PCXMC®) and a 20 year old (a significant lower effective dose estimate with the PCXMC®

version 2.0) respectively, for the effective dose to the thyroid gland, estimated with both

PCXMC® software programs.

Figure 13. Box-and-whisker plots for a 1 year old and a 20 year old of the estimated effective

doses to the thyroid gland, calculated with PCXMC® version 1.5 (E) and version 2.0 (E’).


66


regarding effective dose to the thyroid gland with respect to the projection angles used only.

Version 1.5 vs. version 2.0 30° angle 45° angle 65° angle

30° angle P = 0.0215

45° angle P = 0.0117

65° angle P < 0.0001

From table 20 it is clear that there is a significant difference in the estimated calculations for

the effective thyroid dose, with regard to the angulation of the central X-ray beam, between

the two versions of the PCXMC® software. The values estimated by PCXMC® version 2.0

were significantly lower for the 45° and 65° angle, while the opposite was true for the 30°

angle.

Table 21. Student T-test results of the comparison of the 2 PCXMC® versions regarding

effective dose to the thyroid gland with respect to the exposure settings used only. (NS

stands for no significant difference)

Version 1.5 vs.

version 2.0

kVp*mAs = 70 kVp*mAs = 140 kVp*mAs = 120 kVp*mAs = 240

kVp*mAs = 70 NS

kVp*mAs = 140 NS

kVp*mAs = 120 NS

kVp*mAs = 240 NS


67

No significant differences, whatsoever, were noticed between the 2 PCXMC® calculations

for the effective dose to the thyroid gland, with regard to the 4 different exposure settings

only (table 21).

When age and a 30° central X-ray angulation are taken into account, Student T-tests showed

that the effective thyroid dose, calculated with the PCXMC® version 2.0, was significantly

higher for children aged 1, 5 and 10. The opposite was true for ages 15 and 20.

Similar statistical analysis for effective dose to the thyroid gland calculations for age and a

45° angle of the central X-ray beam, showed significant lower values with the PCXMC®

version 2.0 for ages 1, 5, 15 and 20. For age 10 this was significantly higher.

Statistical analysis for differences in calculations between the two PCXMC® versions for the

estimated effective thyroid dose, with respect to age and a central X-ray beam angulation of

65°, showed a significant lower value calculated with the PCXMC® version 2.0 for all ages.

In figures 14a to 14c box-and-whisker plots are shown of the just mentioned statistical

observations, respectively for central X-ray beam angles 30°, 45° and 65°.


68

age15101520

Box-and-whisker 600

500

400

300

200

100

0

angle = 30E thyroid E' Thyroid

age15101520

Box-and-whisker 350

300

250

200

150

100

50

0


Figure 14a. Box-and-whisker plot of the effective dose to the thyroid gland, as calculated by

the PCXMC® version 1.5 (E) and 2.0 (E’) with respect to age and a 30°angulation of the

central X-ray beam.

Figure 14b. Box-and-whisker plot of the effective dose to the thyroid gland, as calculated by


central X-ray beam.


69

age15101520

Box-and-whisker 140

120

100

80

60

40

20

0


Figure 14c. Box-and-whisker plot of the effective dose to the thyroid gland, as calculated by


central X-ray beam.


regarding effective dose to the oesophagus with respect to the age groups.(NS stands for no

significant difference)

Version 1.5 vs.

version 2.0


1 year old NS

5 year old P = 0.0022

10 year old P = 0.0061

15 year old P = 0.0004

adult P = 0.0010


70

From table 22 it can be derived that except for the one year old, a significant difference was

noticed between the calculations from PCXMC® version 1.5 and version 2.0. The PCXMC®

version 2.0 calculations gave significant lower figures than did the PCXMC® version 1.5

estimates.


regarding effective dose to the oesophagus with respect to the projection angles used .(NS

stands for no significant difference)

Version 1.5 vs. version

2.0

30° angle 45° angle 65° angle

30° angle P < 0.0001

45° angle P < 0.0001

65° angle NS

The conclusion from table 23 is that except for the 65° angle, the estimated doses to the

oesophagus calculated by the 2 PCXMC® versions were significantly different. The PCXMC®

version 2.0 calculated significantly lower values than version 1.5 for X-ray beam angulations

of 30° and 45° respectively.

The estimated total effective dose, as a function of the exposure settings only, was

significantly higher when calculated with the PCXMC® version 2.0 than with version 1.5. for

every exposure setting used in the study (table 24).


71

Table 24. Student T-test results (P-values)of the comparison of the 2 PCXMC® versions

regarding total effective dose with respect to the exposure settings used only.

Version 1.5 vs.

version 2.0

kVp*mAs = 70 kVp*mAs = 140 kVp*mAs = 120 kVp*mAs = 240

kVp*mAs = 70 P = 0.0062

kVp*mAs = 140 P = 0.0061

kVp*mAs = 120 P = 0.0027

kVp*mAs = 240 P = 0.0026


regarding total effective dose with respect to the age groups.(NS stands for no significant

difference)

Version 1.5 vs.

version 2.0


1 year old P = 0.0001

5 year old P = 0.0029

10 year old P = 0.0001

15 year old P = 0.0172

adult NS

Table 25 shows that there were significant differences between the estimated values for

total effective dose, as calculated with the 2 PCXMC® software versions. Except for adults,

the estimated total effective dose was significantly higher when calculated with the PCXMC®

version 2.0 than with version 1.5.


72

angle304565

Box-and-whisker 40

35

30

25

20

15

10

5

0E total E' total

Table 26. Student T-test results (P-values) of the comparison of the 2 versions regarding

total effective dose with respect to the projection angles used only.

Version 1.5 vs. version 2.0 30° angle 45° angle 65° angle

30° angle P = 0.0001

45° angle P = 0.0014

65° angle P = 0.0055

With respect to the projection angle, the total effective dose calculated with the PCXMC®

version 2.0 was always significantly higher than with version 1.5 (table 26 and figure 15).

Figure 15. Box-and-whisker plots of the total effective dose calculated with the two PCXMC®

software programs (version 1.5 presented as E and version 2.0 presented as E’) as a function

of central X-ray beam angulations (30°, 45° and 65°).


73

Box-and-whisker 600

500

400

300

200

100

0E oesophagus E thyroid E' Thyroid E total E' total

Further statistical analysis (Student T-tests) revealed that PCXMC® version 2.0 calculations of

the total effective dose, with regard to age and angulation of the central X-ray beam, were

significantly higher for age 1, 5 and 10. For age 15, this was only true for a 30° angulation of

the central X-ray beam. No statistical significant differences were found for the respective

calculations for age 20.

As an overall view, figure 16 illustrates the differences and similarities of both software

versions of PCXMC® between the calculations of the effective doses to the oesophagus,

thyroid gland and the total effective dose.

Figure 16. Box-and-whisker plots with the effective dose calculations for the oesophagus,

the thyroid gland and the total effective dose for PCXMC® version 1.5 (E) and version 2.0 (E’).


74

CHAPTER 7: Discussion

Data from the Ghent University Dental Outpatient Clinic audit of the geometric projection

technique showed that the upper occlusal and paralleling peri-apical were the two most

often used techniques to assess a dental trauma. The variation and inconsistency in X-ray

beam angulation, together with the exposure settings and the sometimes high number of

radiographs, were obviously a matter of concern. Especially because this was a survey on a

child population, the dose to the thyroid gland was particularly worrying.

It is obvious that the age of a patient also determines what kind of projection geometry is

used. This explains the high prevalence of occlusal radiographs in the younger children

(almost 87%) compared to older children (6.5%). On the other hand, it is not always possible

to obtain the best geometric projection position in an acute emergency situation, especially

with young children. It is also under such circumstances that a thyroid protecting shield is

forgotten. In fact there is a lack of guidelines at the Ghent University Dental Outpatient Clinic

and a thyroid shield is not used standardly. However, taking the literature into account (Rush

and Thompson, 2007)29 and the results of the PCXMC® calculations, it is advisable to use a

thyroid shield for every radiograph, including peri-apicals, for which the primary X-ray beam

is directed to the neck of the patient or when scattered radiation can reach the thyroid

gland. Particularly relevant recent guidelines in the UK, for orthodontists, were issued in

2008. These guidelines emphasize on the fact that thyroid shielding makes a substantial

difference in the effective dose to the thyroid in intra-oral imaging31.

It should be emphasized that the cumulative effect of taking serial radiographs of the same

anatomical region, especially in children, should not be underestimated, even when


75

exposure factors, including kVp, mAs, collimation, geometric projection technique and image

detectors, are adjusted and optimized to child settings1,4,5,29. The present study has shown

that, despite the fact of changing the exposure factors to “supposedly” “better” values and

using a more X-ray sensitive (higher speed) type of film, the dose to the thyroid gland

remained the same. Therefore this study pleas for the mandatory use of thyroid shielding

for any kind of intra-oral radiograph.

The PCXMC® calculations showed to be very helpful in assessing the absorbed organ doses.

The fact that the exposure settings and the characteristics of the X-ray beam and collimator

could be set accurately, should ensure reasonably accurate results.

The significant difference for absorbed dose by the thyroid gland in a 1 year old, compared

to an older subject should be an important signal to the entire dental profession to be

careful when making radiographs in children around that age. The decrease in thyroid

absorbed dose with increasing age, can be explained by the thyroid gland’s position in the

neck during childhood through adolescence and adulthood3. It appeared from the present

study that there is a kind of turning point at the age of 10, at which the thyroid gland

becomes less radiation-sensitive, due to its anatomical position (table 15).

As the PCXMC® software cannot calculate the doses for a 2 or 6 year old, for instance, one

has to rely on careful estimates from the ages to which the software is restricted. The author

suggests to always extrapolate to the lowest age, when assessing the absorbed dose of a

patient. This means that if one wishes to calculate the absorbed dose to the thyroid of a 3

year old, the 1 year old figures should be calculated and not the 5 year olds. The latter can


76

be supported by the fact that one should always expect for the worst, despite the fact that

one peri-apical radiograph is estimated to cause 1 fatal cancer in 10 million6,7,32. This should

be multiplied by 3 for children younger than 10, according to the ICRP guidelines. The

physical appearance of a child should not be forgotten, of course, and a such some 3 year

olds resemble more a 5 year old than their peers. In that case one could obviously use the 5

year old subject’s figures.

However, the younger an individual’s tissues, the more vulnerable they will be to undergo

irreversible changes, so perhaps for children under the age of 5 the risk to develop a fatal

cancer is then 4 or 5 times higher than suggested by the ICRP. The latter may just be a

philosophical discourse. Nevertheless, as professionals working with ionizing radiation

should always keep in mind to obtain the best diagnostic images with the lowest radiation

dose to the patient (ALARP principle and limitation principle), this issue should be considered

important enough.

This study has shown the influence of the vertical X-ray beam angulation on the effective

dose of the thyroid gland, with respect to different patient ages. There is, however no clear

cut rule covering all observations. However, as should be the case in studies like these, the

message should be a warning one: always adjust the exposure settings according to the area

of interest and the physical characteristics of the subject and always protect the thyroid

gland from direct or indirect radiation.

It should be emphasized that the results in the present study are all based on calculations

without taking into account a thyroid protecting shield. It is, however, impossible to


77

estimate what the effective dose to the thyroid gland would be with such a shield.

Therefore, phantom or in vivo measurements with TLDs or other measuring equipment

should be performed, as was done in the study by Rush and Thompson (2007)29. In vivo

studies have two major drawbacks, being that one cannot measure inside an organ and that

measurements, for ethical reasons, cannot be repeated. On the other hand, they have one

big advantage, namely they come as close to the clinical situation as can be. Human cadaver

studies, carried out on children of different ages, could be the ultimate solution. Although, it

may obviously prove to be difficult to obtain.

The whole body absorbed radiation dose estimated with the PCXMC® software version 2.0

was higher than with the previous version. The latter was, generally speaking, not always

true for the effective dose to the thyroid gland. Probably this is due to the fact that in the

Monte Carlo calculations, other factors, such as the salivary glands have been implemented.

This may explain the lower estimated effective dose to the thyroid gland if a vertical X-ray

beam angulation of 30° is used and a higher when an angle of 45° or 65° is used. Perhaps the

steeper the X-ray beam angle, the more it will be in the area of the salivary glands (see figure

1) and the less scattered radiation it will produce, while a less steep angle may cause more

scattering towards the thyroid gland. The latter is merely an assumption and could be

investigated with the PCXMC® software, using more than these three angulations for the

central X-ray beam.

The implementation of “new” weighting factors, implies that one should be very prudent in

interpreting observed differences between the estimates by the two software versions of

PCXMC®. As the PCXMC® version 2.0 software just recently became available (June 2008), it

can be expected that new publications will show up, comparing “older” published values


78

with the new software. However, because of the new weighting factors and because of the

observations from the present study, it is not advisable to compare such data. New

calculations, without comparisons have to be published, instead of comparing with figures

from the past. The old figures are not relevant anymore.


79

CHAPTER 8: Conclusion

This study has proven, by means of retrospective PCXMC® calculations, that without the use

of a thyroid protection shield, there is no significant difference in absorbed dose by the

thyroid gland at exposures of 70 kVp and 1 mAs or 60 kVp and 4 mAs. Therefore the first null

hypothesis is confirmed.

The second hypothesis has to be rejected as there is a significant higher effective dose to

the thyroid when a vertical X-ray beam angulation of 45° is used, compared to a 65°

angulation.

The third null hypothesis has to be rejected as it was shown that children younger than 10

years old received a significant higher effective dose to the thyroid gland than children that

were older. Above the age of 10, no significant difference was found.

The fourth null hypothesis has to be rejected as the estimated effective dose to the thyroid

gland was lower in the PCXMC® version 2.0.

The first conclusion of this study is, that despite of the exposure factors, which may have

been adjusted to children, a thyroid protecting shield should always be used in intra-oral

radiography. The latter seems to have more impact on the estimated effective dose to the

thyroid gland than does the exposure settings, such as kVp and mAs.

The second conclusion of this study is that in the future one should be careful in interpreting

estimated effective doses, as they may be calculated with different weighting factors. The

latter was clearly shown in the present study in which PCXMC® version 1.5 and 2.0 were

compared, for the estimated effective doses to the thyroid gland.


80

REFERENCES

1. Regulla DF, Eder H. Patient exposure in medical X-ray imaging in Europe. Radiat Prot

Dosimetry 2005;114(1-3):11-25.

2. Hart D, Wall BF. UK population dose from medical X-ray examinations. Eur J Radiol

2004;50:285-291.

3. Hujoel P, Hollender L, Bollen AM, Young JD, McGee M, Grosso A. head-and-neck

organ doses from an episode of orthodontic care. Am J Orthod Dentofacial Orthop

2008;133(2):210-217.

4. Angelieri F, de Oliveira GR, Sannomiya EK, Ribeiro DA. DNA damage and cellular

death in oral mucosa cells of children who have undergone panoramic dental

radiography. Pediatr Radiol 2007;37:561-565.

5. Looe HK, Pfaffenberger A, Chofor N, Eenboom F, Sering M, Rühmann A, Poplawski A,

Willborn K, Poppe B. Radiation exposure to children in intraoral dental radiology.

Radiat Prot Dosimetry 2006;121(4):461-465.

6. Whaites E. Essentials of dental radiography and radiology. 4th Ed. Churchill

Livingstone, Elsevier, 2007. London.

7. 7 Selection criteria for dental radiography. Ed. Pendlebury ME, Horner K, Eaton KA.

Faculty of general Dental Practitioners (UK) & The Royal College of Surgeons of

England. 2nd Ed. 2004.

8. McCollough CH, Schueller BA. Calculation of effective dose. Med Phys

2000;27(5):828-837.


81

9. Kramer R, Vieira JW, Khoury HJ, Lima FR, Fuelle D. All about MAX: a male adult voxel

phantom for Monte Carlo calculations in radiation protection dosimetry. Phys Med

Biol 2003;48(10):1239-1262.

10. Draft recommendations of the international commission on radiological protection.

02/276/06 5 June 2006. www.icrp.org

11. Frederiksen NL. Health physics. In: Oral radiology. Principles and interpretation. 5th

Ed. White SC and Pharoah MJ. Mosby, St Louis, Missouri, USA. 2000; chapter 3:47-68.

12. Langland OE, Langlais RP, Preece JW. Radiation biology. In: Principles of dental

imaging. 2nd Ed. Lippincott Williams and Wilkins. Baltimore, Maryland, USA. 2002;

chapter 12:299-314.

13. Graham DT, Cloke P. Radiation Protection. In: Principles of radiological physics. 4th Ed.

Churchill Livingstone, Edinburgh, UK. 2004; chapters 32-33:325-360.

14. Kaeppler G, Dietz K, Herz K, Reinert S. Factors influencing the absorbed dose in

intraoral radiography. Dentomaxillofac Radiol 2007;3(8):506-513

15. Svenson B, Sjöholm B, Jonsson B. Reduction of absorbed doses to the thyroid gland in

orthodontic treatment planning by reducing the area of irradiation. Swed Dent J

2004;28(3):137-147.

16. Aragno D, Fattibene P, Onori S. Dental radiography: tooth enamel EPR dose

assessment from Rando phantom measurements. Phys Med Biol 2000;45(9):2671-

2683.

17. Helmrot E, Alm Carlsson G. Measurement of radiation dose in dental radiology.

Radiat Prot Dosimetry 2005;114(1-3):168-171.

18. Williams JR, Montgommery A. Measurement of dose in panoramic dental radiology.

Brit J Radiol 2000;73:1002-1006.

http://www.icrp.org/�


82

19. Carlsson AG, Carlsson CA, Persliden J. Energy imparted to the patient in diagnostic

radiology: calculation of conversion factors from measurements of the air-collision

kerma integrated over beam area. Phys med Biol 1984;29:1329-1341.

20. Gray JE, Archer BR, Butler PF, Hobbs BB, Mettler FA Jr, Pizzutiello RJ Jr, Schueler BA,

Strauss KJ, Suleiman OH, Yaffe MJ. Reference values for diagnostic radiology:

application and impact. Radiology 2005;235(2):254-358.

21. Kuroyanagi K, Hayakawa Y, Fujimori H, Sugiyama T. Disdtribution of scattered

radiation during intraoral radiography with the patient in a supine position. Oral Surg

Oral Med Oral Pathol Oral Radiol Endod 1998;85(6):736-741.

22. Stenström B, Henrikson CO, Holm B, Richter S. Absorbed doses from intraoral

radiography with special enphasis on collimator dimensions. Swed Dent J 1986;10(1-

2):59-71.

23. Rassow S. From the entrance dose to the calculation of organ doses. Radiat Prot

Dosimetry 1998;80(1-3):327-329.

24. Le heron JC. Estimation of effective dose to the patient during medical X-ray

examinations from measurements of the dose-area product. Phys Med Biol

1992;37:2117-2126.

25. Shannoun F, Zeeb H, Back C, Blettner M. Medical exposure of the population from

diagbosric use of ionizing radiation in Luxembourg between 1994 and 2002. Health

Phys 2006;91(2):154-162.

26. Eder H, Zapf W, Schöfer H. Excess exposure caused by instrumental and operational

failaures – reasons, radiation doses, technical solutions.

www.lgl.bayern.de/arbeitsschutz/doc/jahresberichte/jahresbericht_lfas_02.PDF

http://www.lgl.bayern.de/arbeitsschutz/doc/jahresberichte/jahresbericht_lfas_02.PDF�


83

27. Stratakis J, Damilakis J, Gourtsoyiannis N. Organ and effective dose conversion

coefficients for radiographic examinations of the pediatric skull estimated by Monte

Carlo methods. Eur Radiol 2005;15:1948-1958.

28. Tapiovaara M, Lakkisto M, Servomaa A. PCXMC- A PC based Monte carlo program for

calculating patient doses in medical X-ray examinations. Finnish Centre for radiation

and Nuclear Safety (STUK). 2007

29. Rush ER, Thompson NA. Dental radiography technique and equipment: how they

influence the radiation dose received at the level of the thyroid gland. Radiography

2007;13:214-220.

30. Vieira JW, Kramer R, Lima FRA. Calculation of effective dose from external exposure

to photons for the Male Adult voXel (MAX) phantom. Nucl Instr Meth Phys 2004;654-

657.

31. Abbott P. Are dental radiographs safe? Austr Dent J 2000;45(3):208-213.

32. KG Isaacson, AR Thom, K Horner, E Whaites. Guidelines for the use of radiographs in

clinical orthodontics. British Orthodontic Society. 3rd Ed 2008 ISBN 1 899297 07 3


84

Addendum 1

Thanks, Stu. It sounds like an interesting (although perhaps frustrating) conference. Sharon On 5/2/08 12:45 PM, "Stuart C. White" <[email protected]> wrote:

Hi Sharon, I think the short answer is "yes", what you propose is just fine. The modifications you suggest, using rectangular collimation and fast receptor, are, of course exactly correct and the issue of individual variability as described by Alan and Julian is true as well. I recently returned from a most interesting two-day conference at the NCRP entitled, “Low Dose and Low Dose-Rate Radiation Effects and Models.” A somewhat less formal title would be, “What is the state of the Linear Nonthreshold Hypothesis?” While I cannot summarize the entire meeting, my take on the consensus opinion of the speakers pertinent to this topic is that one photon will cause 10-20 closely clustered ionizations. When this cluster occurs in a cell nucleus it may result in complex DNA breakage, double-strand breaks that may result in translocations or loss of coding information. Such damage may or may not be viable but when it is it may result in carcinogenesis. At the level of cell-cell interactions there is much evidence for bystander effects and genomic instability at very low doses. What is far, far less clear, however, is how the whole organism deals with such damaged cells. There is evidence, for instance, of radiation induced apoptosis, as well as immune surveillance. The biologists looking at this question say that the only sure answers can come from epidemiological studies. The epidemiologists say that their sample sizes can never be large enough to answer the risk question in the low dose range thus the answers must come from the biologists. Hmm . . . The consensus bottom line seemed to be that there in insufficient evidence to support a threshold model and thus a linear extrapolation risk model is still the most appropriate. The proceedings of the meeting are available from NCRP at <http://www.ncrponline.org/>. Stu On 5/2/08 5:55 AM, "Sharon Brooks" <[email protected]> wrote: > Hello, Friends > > Periodically I provide some answers to the "Ask the Experts" feature of the > Health Physics Society website. I received one question today that I wanted > to check with some of my colleagues before I replied. > > The questioner is a dentist who is concerned about the effective dose of > taking multiple periapical radiographs of a single area (such as during > endodontic therapy). Is is "legal" to take the published effective dose for > a full-mouth series, divide by the number of films in the series to get the > E for a single film, then multiply that number by the number of radiographs > taken to get the E for the endo series?

http://www.ncrponline.org/�


85

> > I suspect that if you wanted to be ultra-precise, you would have to know > exactly which tooth was involved to figure out the amount of bone marrow, > thyroid, salivary gland exposed, as well as account for the time period of > the radiographs. > > Is it worth it to try to be that precise? If we look at published studies on > effective dose for a variety of imaging techniques, there is a fair amount > of variability due to exact placement of the dosimeters, use of 1990 vs 2007 > ICRP, etc. > > The questioner commented at the end that he worries about "these unique > scenarios and the effect they may have on my patients." In my reply, I am > going to mention (gently) that if he is really worried, he needs to make > sure that he is using the fastest film or digital and rectangular > collimation. > > Thanks for your help. > > Sharon > > ***************************** > Sharon L. Brooks, DDS, MS > Diplomate, American Board of Oral and Maxillofacial Radiology > University of Michigan School of Dentistry > Department of Periodontics and Oral Medicine > Ann Arbor, MI 48109-1078 USA > Tel: +1 734-764-1595 Fax +1-734-764-2469 > [email protected] > > > _______________________________________________ > Oradlist mailing list > [email protected] > http://lists.ucla.edu/cgi-bin/mailman/listinfo/oradlist

_______________________________________________ Oradlist mailing list [email protected] http://lists.ucla.edu/cgi-bin/mailman/listinfo/oradlist

_______________________________________________ Oradlist mailing list [email protected] http://lists.ucla.edu/cgi-bin/mailman/listinfo/oradlist

http://lists.ucla.edu/cgi-bin/mailman/listinfo/oradlist�

http://lists.ucla.edu/cgi-bin/mailman/listinfo/oradlist�

Documents

THYROID GLAND ABSORBED RADIATION DOSE …lib.ugent.be/fulltxt/RUG01/001/376/223/RUG01-001376223_2010_0001... · THYROID GLAND ABSORBED RADIATION DOSE FROM INTRA-ORAL RADIOGRAPHS IN