ESTRO 31 S537

of the radioligand was estimated using three ROI delineation methods

varying in complexity and execution time. ROIs were drawn on a)

antero-posterior compressed PET images (AP), b) subsamples of the

organs (S), and c) a 3D-volume covering the whole-organ (W).

Residence times for each organ were calculated from the time course

of the radioligand. The OLINDA/EXM software package was used to

obtain dosimetry estimates.

Results: Measured time activity curves (TACs) showed a close

agreement with the simulated TACs when S and W ROI delineation

methods were used. When the AP method was used, measured TACs

displayed higher activity than simulated TACs in the organs where the

ROI enclosed the whole-organ (heart, lungs, liver and kidneys). The

radiation-absorbed dose (AD) from the critical organ (liver), the

effective dose equivalent (EDE) and the effective dose (ED) estimates

using S and W methods were comparable to the simulated values

(theor.) while the AP method yielded higher AD, EDE and ED estimates

(table 1).

Conclusions: ED estimations are sensitive to the delineation method

applied. 3D methods (S and W) provided the most accurate dosimetry

estimates while the AP method yielded higher dosimetry estimates

because of overlapping between ROIs. The S method showed the best

trade-off between accuracy and practical implementation.

EP-1412

DOSIMETRIC CHARACTERIZATION OF A CONE-BEAM CT FOR

RADIOTHERAPY

T. Martínez Jurado1

, D. Rodríguez Latorre1

, N. Jornet1

, A. Ruiz1

, A.

Latorre Musoll1

, P. Carrasco de Fez1

, T. Eudaldo1

, M. Ribas Morales1

1

Hospital de la Santa Creu i Sant Pau, Servei de Radiofísica i

Radioprotecció, Barcelona, Spain

Purpose/Objective: Many of the currently available linear

accelerators have a gantry mounted kV cone-beam CT (CBCT) with a

wide beam. The dosimetric characterization is not straightforward as

standard CT dosimetric indices and dose measurement equipment are

designed for narrow collimation widths. The aim of this work was to

characterize our CBCT for CT dose considerations by measuring the

dose profile in a long phantom and to quantify the differences in the

measurement of CTDIw index when using different detectors and

phantoms.

Materials and Methods: Measurements were performed on a Clinac

2100C/D (Varian Medical Systems) equipped with a kV imaging OBI

system v1.5 in the pre-defined pelvis mode: 125 kV, 680 mAs and 20.6

cm nominal beam width (y1=y2=10.3 cm).We used a 15 cm long CTDI

standard body phantom and a 45 cm cylindrical phantom made by

joining three CTDI standard body phantoms. Measurements were

performed using two detectors: a solid-state detector RTI CT Dose

Profiler and a CT pencil ion chamber 100 mm long PTW Freiburg

M30009-0186. We measured dose profiles along the couch axis at the

centre and periphery of the 45 cm long phantom point by point with

the solid state detector; we used a spatial resolution of 1 cm and

recorded the dose of a complete axial scan in every point. The couch

was moved over a range of 46 cm. The phantom always covered the

whole beam width at the isocenter. We also made dose measurements

at the centre and the periphery of the phantom, first using the pencil

ion chamber and the 15 cm long phantom, and then using the 45 cm

long phantom. To calculate CTDIw and CTDIw,∞, and determine CTDIw

efficiency we applied IEC 2009 and recent IAEA Human Health Reports

Nº 5 definitions.

Results: Measures performed using a 15 cm long phantom

underestimated CTDI100 by 0.78 in the centre and by 0.95 at the

periphery compared to measures made in a 45 cm long phantom. (see

Table 1). CTDIw was underestimated by 0.91. Our determined CTDIw

were larger than the CTDIw data by Varian. Although there was a

significant difference, the CTDIw values obtained are compatible with

those reported by other authors. By means of the dose profile we

calculated the CTDIw, which was similar to the CTDIw measured with

the pencil ion chamber and the 45 cm long phantom. We also

calculated the CTDIw,∞ defined as the weighted CTDI, considering

the whole dose profile, and the CTDIw efficiency given by the ratio

between the CTDIw and the CTDIw,∞.

Conclusions: CT dosimetric indices are underestimated when

dosimetric parameters and dose measurement equipment designed for

narrow collimation widths are applied to CBCT as the phantom and

the detector lengths are smaller than the whole beam. Therefore,

only a part of the primary radiation and a part of the scattered

radiation are measured. Measuring the dose profile with a solid

detector in a 45 cm long phantom is an accurate method to

characterize the properties of the CBCT. However, a special phantom

is required and about 2h of treatment unit per profile are needed.

EP-1413

ACCEPTANCE TESTS PROCEDURE VERSUS CLINICAL IMAGING QUALITY

ASSURANCE FOR KV-CBCT IMAGE SYSTEM

J. Galhardas1

, R. Malveiro1

, M.E.R. Poli1

1

University Hospital Santa Maria, Medical Physics Unit, Lisboa,

Portugal

Purpose/Objective: The aim of this study is to compare the imaging

acceptance tests procedure (ATP) from manufacturer to the imaging

quality assurance (QA) for clinical imaging setup (preset) using

imaging quality parameters (defined on the clinical presets) to deliver

a kV cone-beam CT (CBCT) adequate for clinical use.

Materials and Methods: The kV-CBCT images were acquired using the

Elekta Synergy S linac with integrated X-ray Volume Imaging (XVI)

system.Tests were performed in a Catphan 600 phantom and a TOR

18FG (Leeds) phantom X-ray imaging with 1 mm Cu filter.

The ATP was performed according to the manufacturer instructions

and for the clinical imaging QA, the tests were: (1) 3D Uniformity, (2)

3D Low contrast visibility, (3) 3D Spatial Resolution, (4) 3D Transverse

vertical and (5) horizontal scale, (6) 3D Sagittal geometric, (7) 2D Low

contrast visibility, (8) 2D Spatial resolution and (9) Imaging doses

using CBCT dose index (CBDI).

For both, ATP and clinical imaging QA, the material and equipment

setup used to perform both set of tests were the same and all the

tests were performed under the same conditions (e.g. heat units

between 4% and 7%).

The differences between the ATP and clinical QA tests relied on the

imaging quality parameters such as detector resolution,

S538

reconstruction algorithm, acquisition angle and kV tha

the presets. The ATP required specific presets and th

the presets available for clinical routine.

Imaging doses were estimated for each preset using

TM30009 PTW and a cylinder phantom with 16 cm

Delivery time, reconstruction time and image s

evaluated.

Results: Table 1 shows the results for both ATP and

different presets. Using the same tolerances from ATP

the kV-CBCT QA fail for all the clinical presets. In ord

in these tests, the imaging quality parameters of the

were changed. By increasing the detector resol

acquisition angle, the quality of CBCT image can be im

impact was the increase of dose, delivery time, reco

and image size on disk, up to 70%, 66%, 1090% and 334%

Test Parameter

ATP

Preset

Head

and

Neck

S20

Chest

M20

Pelvis

M20

Prosta

M15

ATP QA QA QA QA

1 uniformity P F F F F

2 contrast P F F F F

3 resolution P F F F F

4 scale P P P P P

5 scale P P P P P

6 scale P P P P P

7 contrast P P P P P

8 resolution P P P P P

Table 1 - Results for ATP and clinical QA tests, where

is Fail.

Conclusions: The tolerances from ATP could not be

the clinical tests and should not be used as reference

QA. Performing an imaging QA for clinical presets is an

to define references for quality control tests and to im

images based on clinical routine.

One can note that image system used in radiotherapy

pass the acceptance tests but fail the intent for its pur

EP-1414

THE SECONDARY EXPOSED DOSE PRODUCED BY THE V

GUIDED RADIATION THERAPY SYSTEMS

T. Isobe1

, K. Takada1

, E. Sato1

, K. Shida1

, D. Kobayashi

Mori1

, H. Sakurai1

, T. Sakae1

1

University of Tsukuba, Graduate School of Comprehen

Sciences, Tsukuba, Japan

2

Tsukuba University Hospital, Department of Radiology

Japan

Purpose/Objective: Image-Guided radiation thera

reduce the setup error in radiation therapy and the c

increasing. On the other hand, various systems to achi

produce an excessive exposed dose. It is anxious abo

the carcinogenic risk by this excessive exposed dose. I

compared the secondary exposed dose associated wi

systems.

Materials and Methods: In this study, we measured

exposed dose produced by various IGRT systems

dosimeters and the human phantom. The glass dosime

because it is possible to measure at several points

phantom. The system used in this study was the

accelerator (Varian Medical Systems, Palo Alto, CA)

First, we verified the precision of glass dosimeter.

measured value of glass dosimeters with calibr

chamber using the X-ray simulator (Toshiba Medical S

In consideration of the X ray energy generated from

simultaneous irradiation of these detectors was perfo

X ray energies (40 kV-120 kV), and measured values w

Next, the secondary exposed dose produced by vario

(Orthogonal On-board Image, Cone beam CT, Ex

measured. We placed the glass dosimeters on cent

(anterior, left side, right side, posterior) of a phantom

were performed 3 times respectively. The parameters

at are defined in

he QA tests used

an ion chamber

m of diameter.

size were also

d clinical QA for

P, tests 1 to 3 of

der to get a pass

clinical presets

lution and the

mproved but the

onstruction time

% respectively.

ate

ATP

tolerance

≤1.5%

≤1.5%

≥10 lp/cm

±1.0mm

±1.0mm

±1.0mm

≥12 discs

≥1.4 lp/mm

e P is Pass and F

achieved during

e for the clinical

n important step

mprove kV-CBCT

can successfully

rpose.

VARIOUS IMAGE-

2

, K. Suzuki2

, Y.

nsive Human

y, Tsukuba,

py (IGRT) can

clinical utility is

eve an IGRT will

out elevation of

n this study, we

ith various IGRT

d the secondary

with the glass

eter was chosen

s in the human

e Trilogy linear

We related the

ated ionization

Systems, Japan).

m IGRT systems,

ormed in various

were compared.

us IGRT systems

xactrac®) were

er and surfaces

m. Measurements

of imaging were

applied the clinical settings. Dose evaluation

kerma.

Results: As a result of comparing glass dosim

chamber, the glass dosimeters have underest

maximum compared to the ionization cha

produced by each IGRT systems became t

mGy, OBI=11.01 mGy, and Exactrac =1.34 m

dose, it became the highest by CBCT=18.88 m

about secondary exposed dose associated

documented. The result of present study (29

18.88 mGy at the center) was consistent

(Table 1) If it is performed daily CBCT

fractions), we can estimate that it become

dose of 1.1 Gy at the center and 0.7 Gy at

most of secondary exposed dose associated

CBCT, it is necessary to take into account

parameters of CBCT to reduce the patient do

Table 1 Comparison of the secondary expos

CBCT

absorbe

surface

present study 29.75

Wen N, et al.

(Phys Med Biol. 52, 2007 ) 30~60

Song WY, et al.

(Med Phys. 35, 2008) n.e.

Amer A, et al.

(BJR. 80, 2007) 21~34

Islam MK, et al.

(Med Phys. 33, 2006) 23

n.e. : not estimated

Conclusions: The secondary exposed dose

IGRT systems was highest in CBCT, and it be

of OBI, and Exactrac. In the case of per

prostate IMRT, it was suggested that the seco

1.1 Gy at the center and 0.7 Gy at the surfac

EP-1415

COMPUTATIONAL LYMPH NODE MODELS IN RE

RADIONUCLIDE THERAPY DOSIMETRY

S. Lamart1

, M.B. Wayson2

, W.E. Bolch2

, C. Lee

1

National Cancer Institute National Institutes

Cancer Epidemiology and Genetics, Rockville

2

University of Florida, J. Crayton Pruitt Fami

Biomedical Engineering, Gainesville FL, USA

Purpose/Objective: Explicit radiation dose c

the lymphatic node system in nuclear medic

using surrogate tissues since its computatio

available in traditional stylized phantoms

existing clinical dosimetry tools such as OL

develop a new lymph node model within a ne

human phantoms, called hybrid phantoms,

examples of its application to radionucl

Materials and Methods: The lymph node mod

ESTRO 31

was performed by the air

meters with an ionization

timated about 9.6% at the

mber. The surface dose

he order of CBCT=29.75

mGy. Also in the central

mGy. (Fig. 1) The reports

with CBCT were well-

9.75 mGy at the surface,

with the other reports.

for prostate IMRT (39

es the secondary exposed

the surface. Because the

d with IGRT depends on

t the frequency and the

se to healthy tissue.

sed dose associated with

ed dose (mGy)

center

18.88

n.e.

16

21

16

associated with various

ecame lower in the order

rforming daily CBCT for

ondary exposed dose were

ce of the human phantom.

EFERENCE PHANTOMS FOR

e1

s of Health, Division of

MD, USA

ily Department of

calculation accounting for

cine has been performed

onal model has not been

which are the basis of

LINDA. This work aims to

ew class of computational

and to show illustrative

lide therapy dosimetry.

dels were developed for a