International Atomic Energy Agency Medical exposure in radiology: Guidance or Reference Levels Module VIII.3 - Part 4: Guidance levels for the patients

International Atomic Energy Agency

Medical exposure in radiology:Medical exposure in radiology: Guidance or Reference Levels Guidance or Reference Levels

Module VIII.3 - Part 4: Guidance levels for the patients

Guidance levelsModule VIII.3 Part 4: Guidance levels for patients

2 International Atomic Energy Agency

IntroductionIntroduction

• In general, in medical exposure there are no dose limits or constraints

• Dose reference (DRL) or guidance levels are tools to optimize procedures and equipment use

• We will see how to establish them and give some examples of values and discuss their usefulness



TopicsTopics

1. Medical Exposure

2. Medical exposure framework and reference doses

3. Medical exposure dose constraints for comforters and in research



OverviewOverview

• Overview of types of radiation exposure

• Dose limits, dose constraints

• Justification and optimization

• Dose guidance/reference level definition

• How to establish them

• How to use them

• Examples of dose reference levels


Topic 1: Medical exposure Topic 1: Medical exposure framework and reference dosesframework and reference doses



Types of exposureTypes of exposure

• Medical Exposure:• principally the exposure of persons as part of their

diagnosis (or treatment)

• Occupational Exposure: • exposure incurred at work, and practically as a

result of work

• Public Exposure:• all other exposures



What is a medical exposure?What is a medical exposure?

• Exposure of persons as part of their diagnosis or treatment

• Additionally:• Exposures (other than occupational) incurred

knowingly and willingly by individuals such as family and close friends helping either in hospital or at home in the support and comfort of patients

• Exposures incurred by volunteers as part of a program of biomedical research



What is occupational exposure?What is occupational exposure?

All exposures of workers incurred in the course of their work.

[excepted the exposures excluded from the Standards (see Basic Safety Standards) and exposures from practices or sources exempted by the Standards]



What is exposure of the public?What is exposure of the public?

• ALL exposures not falling in the two other categories

• effective dose of 1mSv in a year

• in special circumstances, effective dose of 5mSv in a single year, provided that the average over five consecutive years in less than 1mSv per year

• equivalent dose to lens of the eye 15mSv in a year

• equivalent dose to skin of 50mSv in a year



Overview Dose limits (ICRP60)Overview Dose limits (ICRP60)

Occupational dose limit

Public dose limit

Effective dose20mSv/y, averaged

over 5 y1 mSv/y

Annual effective dose in:

Lens of eye 150mSv 15mSv

Skin 500mSv 50mSv

Hands and feet 500mSv -


Topic 2: Medical exposure Topic 2: Medical exposure framework and reference doses framework and reference doses



Question 1Question 1

• Mr. Sharp, I am given to understand that 2 CT examinations performed on me have given me 25 mSv whereas 20 mSv is the safe dose. I want to file legal suit against the doctor.

What do you feel ??



Question 2Question 2

My resident doctor has got 12 mSv in her last badge report as she was wearing the badge while getting her barium study. She wants off from radiation work.

?????



Medical exposure frameworkMedical exposure framework

• Justification

• Optimization

• The use of doses limits is NOT APPLICABLE

• As an aid to keep doses as low as reasonably achievable:

•Dose constraints and guidance (or reference) levels ARE RECOMMENDED



Justification: 3 levelsJustification: 3 levels

• General level:• Use of radiation in medicine is doing more good

than harm

• Generic level:• By national professional bodies

• Specific procedure with a specific objective: chest radiographs for patients showing relevant symptoms

• Individual level:• Application of the procedure to an individual patient

Review benefits and disadvantages !



Sharing responsibility: Sharing responsibility: the referring physicianthe referring physician

• A useful investigation is one in which the result —positive or negative — will alter management or add confidence to the clinician’s diagnosis.

• The chief causes of the wasteful use of radiology are:• Repeating investigations which have already been done

• Investigation when results are unlikely to affect patient management

• Doing the wrong investigation

• Failing to provide appropriate clinical information and questions that the imaging investigation should answer

• Doing the wrong investigation.

• The responsibility for patient dose is shared by the radiology department AND the referral physician



OptimizationOptimization

• Optimization is usually applied at two levels:

• The design and construction of equipment and installations

• Day to day radiological practice (procedures)

• The optimization means that doses should be “as low as reasonably achievable, economic and social factors being taken into account” compatible with achieving the required objective

• The optimization of protection in diagnostic radiology does not necessarily mean the reduction of doses to the patient (ex: antiscatter grid)

• Since no dose LIMITS, there is a need for indicator for optimization:

GUIDANCE LEVELS



What is a guidance or reference level?What is a guidance or reference level?

• A value of dose, dose rate or activity selected by professional bodies in consultation with the Regulatory Authority to indicate a level above which there should be a review by medical practitioners in order to determine whether or not the value is excessive, taking into account the particular circumstances and applying sound clinical judgment (BSS)

ORdose levels in medical radiodiagnostic practices for typical examinations for groups of standard-sized patients or standard phantoms for broadly defined types of equipment; these levels are expected not to be exceeded for standard procedures when good and normal practice regarding diagnostic and technical performance is applied (Med. Direct. EUR97/43)



Guidance levelsGuidance levels

The guidance levels are intended:

(a) to be a reasonable indication of doses for average sized patients

(b) to be established by relevant professional bodies in consultation with the local Regulatory Authority

(c) to provide guidance on what is achievable with current good practice rather than on what should be considered optimum performance

(d) to be applied with flexibility to allow higher exposures if these are indicated by sound clinical judgement

(e) to be revised as technology and techniques improve



Use of the dose reference levels (DRL)Use of the dose reference levels (DRL)

• Act as investigation levels, triggering a local investigation if typical dose for specific type of diagnostic procedure is found consistently to exceed the relevant DRL

• Simple test for identifying situations where patient doses are becoming unusually high and action is required

• Corrective action is compulsory: on the procedure, on the equipment,…



Other practical aspectsOther practical aspects

• Quantities used as guidance (or reference) levels should be understood by radiologists and radiographers (safety culture)

• DRL are not applicable to individual patients. Comparison with DRL shall be only made using mean values of a sample of patients

• DRL should be "flexible" (tolerances should be established: different patient sizes, different pathologies, etc). DRL are not a border line between good and bad medicine

• The main objective of DRL is their use in a dynamic and continuous process of optimization



How to set the DRL value?How to set the DRL value?

• Pragmatic: use the 3rd quartile value of wide scale surveys

• If 75% of X Ray depths can operate satisfactory BELOW

• The remaining 25% should be made aware of their less than optimum performance

• ICRP73 recommended that:“...initialDRL values be chosen as a percentile point on the observed distribution of dose to patients.”

• The “Nordic Guidance Levels for Patient Dose in Diagnostic Radiology” (1996) uses values closer to the mean value



When no surveys are available?When no surveys are available?

• Do not reinvent the wheel

• Regulating Authority/Professional body can adopt DRL’s from country with similar medical infrastructure



Why no LOWER level?Why no LOWER level?

• Examinations with very low exposure usually give not enough diagnostic information, why no lower limit?

• DRL checks forms part of QA program

• Such program will include more than dose criteria

• Including image quality and diagnostic efficacy



Dose quantities for monitoring ESD Dose quantities for monitoring ESD

• Conventional radiology

• ESD Entrance surface dose• TLD attached to skin where centre of X Ray beam

enters patient

• Or calculated from output measurements made in free air with ionization chamber during QA procedures corrected for backscatter (in radiology between 1.2-1.4)



Dose quantities for monitoring: DAPDose quantities for monitoring: DAP

• Conventional and fluoroscopy• DAP Dose area product meter

• Attached to diaphragm housing

• Total DAP value (radiography + fluoroscopy) can be read out per examination or as time sequence

• For fluoroscopy DRL are sometimes given in “Dose RATE Guidance Levels”



Dose quantities for monitoring: CTDose quantities for monitoring: CT

• Computed tomography• Weighted CTDI per CT

slice (analog to ESD)

• Dose-Length product per exam (analog to DAP)

• Multiple San Dose Average (MSAD)

• Can only be determined on phantoms, not on patients

Do

se

Nominal slice width

CTDI

Dose profile

MSAD



Examples of guidance levelsExamples of guidance levels



Guidance or reference levels for diagnostic Guidance or reference levels for diagnostic radiography (typical adult patient)radiography (typical adult patient)

1.5Chest LAT

0.4Chest PA

10Hip joint AP

10Pelvis AP

Entrance surface dose per radiograph (mGy)

Examination




5Dental AP

7Dental peri-apical

20Thoracic spine LAT

7Thoracic spine AP


Examination




Dose values are in air with backscatter. They are for conventional film-screen combination (200 speed

class). For higher speed film-screen combinations (400-600), the values should be reduced by a factor of 2 to 3.

3Skull LAT

5Skull AP


Examination



Dose guidance levels in CT Dose guidance levels in CT (typical adult patient)(typical adult patient)

(a) Derived from measurements on the axis of rotation in water equivalent phantoms, 15 cm in length and 16 cm (head) and 30 cm (lumbar spine and abdomen) in diameter.

25Abdomen

35Lumbar spine

50Head

Multiple scan average dose (mGy) (a)

Examination



Determined in a 4.5 cm compressed breast consisting of 50% glandular and 50% adipose tissue, for film-screen systems and dedicated Mo-target/Mo-filter

mammography units

1 mGy (without grid)

3 mGy (with grid)

Average glandular dose per craniocaudal projection

Dose guidance levels for Dose guidance levels for mammographymammography



Dose rate guidance levels for fluoroscopy Dose rate guidance levels for fluoroscopy (typical adult patient)(typical adult patient)

(a) In air with backscatter

(b) For fluoroscopes that have an optional 'high level' operational mode, such as those frequently used in interventional radiology

100High Level (b)

25Normal

Entrance surface dose rate (mGy/min) (a)

Operation Mode



DRL’s in Pediatrics, for standard five-year-old DRL’s in Pediatrics, for standard five-year-old patients, for single viewspatients, for single views

(from EUR-16261)(from EUR-16261)

Radiograph

5-year old patient.Reference Dose

Entrance Surface Doseper SINGLE VIEW. [µGy]

Chest Posterior Anterior (PA) 100

Chest Anterior Posterior (AP, for non-co-operative patients)

100

Chest Lateral (LAT) 200

Chest Anterior Posterior (AP NEWBORN) 80

Skull Posterior Anterior/ AnteriorPosterior (PA/AP)

1500


Special casesSpecial cases

Medical exposure dose constraints for comforters and in research



Medical exposure dose constraintsMedical exposure dose constraints

• For medical exposure normally no dose constraints are used, only guidance levels

• Only for the protection of persons exposed for medical research purposes, or of persons, other than workers, who assist in the care, support or comfort of exposed patients dose constraints are applicable



Helping personsHelping persons

• Severely ill patients require assisting persons

• Partially cooperating pediatric patients, especially after trauma or with severe pain, need holding persons to stabilize the patient’s position for exact exposure

• Ideally, no holding persons should be involved in radiography and fluoroscopy of patients

• If at all possible, the helping person should be a technician or a nurse

• Parents present can and often will hold their child

• If female persons assist the radiographer or the radiologist, they should be asked about a possible pregnancy.



Medical researchMedical research

•The exposure of humans for medical research is deemed to be not justified unless it is:

•(a) in accordance with the provisions of the Helsinki Declaration16 and follows the guidelines for its application prepared by CIOMS and WHO;

•(b) subject to the advice of an Ethical Review Committee (or any other institutional body assigned similar functions by national authorities) and to applicable national and local regulations.

( CIOMS: Council for International Organizations of Medical Sciences)



What we learnedWhat we learned

• Medical exposure is not subjected to dose limits

• Basic principle is to comply with ALARA, justification and optimization

• Dose reference levels are tools to optimize procedures and equipment use

• A regular check has to be made of actual given doses with DRL’s

• Examples are given of accepted DRL’s for standard patients and common procedures

• Dose constraints are applicable for comforters and persons exposed in research



Where to get more informationWhere to get more information

• International Basic Safety Standards for Protection Against Ionizing Radiation and for the Safety of Radiation Sources. 115, Safety Standards. IAEA, February 1996.

• Radioprotection 102. Implementation of the medical Directive 97/43. pp 78-84 Available at website: http://europa.eu.int/comm/environment/pubs/nuclear.htm#radiationprotection)

• Referral Criteria for Imaging. Radiation Protection 118. Adapted by experts representing European Radiology and Nuclear Medicine. In conjunction with the UK Royal College of Radiologists. Coordinated by the European Commission. Directorate General for the Environment. Luxembourg, 2000. Available at:website http://europa.eu.int/comm/environment/radprot



Where to get more informationWhere to get more information

• ICRP 73. Radiological Protection and Safety in Medicine. Annals of the ICRP, 26(2), 1996.

• WORLD HEALTH ORGANIZATION, Use of Ionizing Radiation and Radionuclides on Human Beings for Medical Research, Training and Non-Medical Purposes, Technical Report Series No. 611, WHO, Geneva (1977).

Documents

International Atomic Energy Agency Medical exposure in radiology: Guidance or Reference Levels Module VIII.3 - Part 4: Guidance levels for the patients