Development of a radiophotoluminescent glass plate detector for small field dosimetry Araki F....

Development of a radiophotoluminescent glass plate detector for small field dosimetry

Araki F. ([email protected])Kumamoto University School of Medical Sciences

Ikegami T. and Ishidoya T. Asahi Techno Glass Co.

Moribe N., Shimonobou T. and Yamashita Y.

Kumamoto University Hospital

Miyazawa M.R-Tech Co.KUSMKUSM

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BACKGROUND

• The small field measurements are generally performed using a small active volume diode detector, a small thermoluminescent dosimeter (TLD) or a film dosimeter.

• Recently, a radiophotoluminescent (RPL) glass rod dosimeter (GRD) has also become commercially available.

• However, the output factor measurements of small fields are generally tedious and difficult due to the sharp radial dose fall-off, the small size of the dose plateau region and the lack of lateral electron equilibrium. 2

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• We have been developed a radiophotoluminescent (RPL) glass plate dosimeter (GPD) as a new device for small field dosimetry.

• The GPD is able to measure both the output factor and the dose distribution simultaneously. This device has an advantage over a film dosimeter and other detectors.

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BACKGROUND

PURPOSE

To estimate the usefulness of GPD developed as a new device for the dosimetry of small radiosurgery fields.

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• The dose distribution measured with GPD is compared to those of film dosimeters for 2, 5, 9 and 15 mm circular collimators created by a linear accelerator-based radiosurgery system.

• The GPD output factors are evaluated by comparing them to various detectors, including a p-type silicon diode detector, a diamond detector, GRD and an ion chamber for small circular collimators.

• The results measured with GPD are also compared to those of Monte Carlo simulations.

METHODS

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MATERIALS

RPL glass dosimeter (=2.61, Z =12.04)

Glass plate dosimeter:

30 mm square×1 mm thickness

Glass rod dosimeter (GD-301) :

1.5 mm diameter×8.5 mm length

Film dosimeter

Kodac X-Omat V (XV-2)

GAFCROMIC XR type R 6KUSMKUSM

Hi-pSi stereotactic field detector (SFD) 　 0.6 mm diameter×0.06 mm thickness

PTW diamond detector 3.05 mm diameter×0.26 mm thickness

PTW 31002, 0.125 cm3 ion chamber　　 5.5 mm diameter×6.5 mm length

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MATERIALS

Incident electron histories to target 5 x 5 cm2 field size 4 MV: 5 x 108

10 MV: 1 x 108

Voxel sizes for DOSXYZ 1 mm x 1 mm x 5 mm

Circular collimator sizes 20 mm, 15 mm, 9 mm, 5 mm, 2 mm

Primary collimator

Flattening filter

Monitor chamber

Mirror

Jaws

Circular collimator

Water phantom

Target

Phasespace 1

Phasespace 2

Electron beam

Monte Carlo modeling for a Varian Clinac 2100C accelerator using EGSnrc code BEAMnrc

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AE=ECUT=0.700 MeVAP=PCUT=0.010 MeVPhoton interaction forcing: offRayleigh scattering: offVariance reduction technique Electron range rejection: 4 MV target: ESAVE=0.7 MeV other CMs: ESAVE=1.0 MeV 10 MV target: ESAVE=0.7 MeV other CMs: ESAVE=2.0 MeV Selective bremsstrahlung splitting (SBS):

Nmin=40, Nmax=400 Russian roulette of secondary electron: off

Calculation parameters for simulating 4 and 10 MV photon beams

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Incident electron for 4 MV photon beam

Energy and spread: 4.2 MeV and FWHM of 3%

Radial intensity distribution: FWHM of 1.2 mm

Incident electron for 10 MV photon beam

Energy and spread: 10.3 MeV and FWHM of 3%

Radial intensity distribution: FWHM of 1.5 mm

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Parameters of the electron beam incident on the target for 4 and 10 MV photon beams

Block diagram of a radiophotoluminescence (RPL) readout system

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- 15 - 10 - 5 0 5 10 15

X- axis (mm)

Rel

ativ

e do

se

GPDXV- IIGAF XREGSnrc

4 MV, 15 mm, depth=5 cm

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- 15 - 10 - 5 0 5 10 15

X- axis (mm)

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Comparison of dose profiles between GPD and film dosimeters and EGSnrc

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X- axis (mm)

Rel

ativ

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0.00.10.20.30.40.50.60.70.80.91.01.1

- 12 - 8 - 4 0 4 8 12X- axis (mm)

Rel

ativ

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- 8 - 6 - 4 - 2 0 2 4 6 8

X- axis (mm)

Rel

ativ

e do

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0.00.10.20.30.40.50.60.70.80.91.01.1

- 8 - 6 - 4 - 2 0 2 4 6 8

X- axis (mm)

Rel

ativ

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0.00.10.20.30.40.50.60.70.80.91.01.1

- 3 - 2 - 1 0 1 2 3

X- axis (mm)

Rel

ativ

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Comparison of energy dependence between GPD and other detectors

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60Co 4 MV 10 MV

SFD 1.000 1.006 0.944

GRD 1.000 1.006 0.987

Diamond 1.000 0.969 0.954

GPD 1.000 1.008 1.015

Comparison of o output factors between GPD and other detectors

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0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 5 10 15 20 25

Circular collimator size (mm)

Ou

tpu

t fa

cto

r

Ion chamberSFDGRDDiamondGPDEGSnrc

4 MV

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 5 10 15 20 25


Out

put f

acto

r


10 MV

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Output factors normalized to a 10 x 10 cm2 field

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0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 5 10 15 20 25


Ou

tpu

t fa

cto

r


4 MV

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 5 10 15 20


Ou

tpu

t fa

cto

r


4 MV

Energy dependence for a SFD diode detector

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Output factors normalizedto a 10 x 10 cm2 field

Output factors normalizedto a 20 mm field

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RESULT

• The GRD profiles are found to coincide well with the dose distribution for Kodak XV2 film and GAFCHROMIC XR film dosimeters and Monte Carlo simulations in 4 and 10 MV x-ray beams.

• The GPD response shows little energy dependence in photon energies of a 60Co beam, 4 MV (TPR20,10=0.617) and 10 MV (TPR20,10=0.744) x-ray beams.

• The output factors measured with GPD are in agreement with the diode detector and the GRD with a small active volume, and Monte Carlo simulations. 19

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DISCUSSION

• The GPD system has an advantage over a film dosimeter and other detectors, because it is able to measure both the absolute dose and the dose profiles simultaneously.

• The GRD is expected as a new device for small field and IMRT dosimetry.

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CONCLUSIONS

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• It is found that GPD is a very useful detector for small field dosimetry, in particular, less than 10 mm circular fields.

• Another purpose of this work is to apply more wide glass plate detectors to IMRT dosimetry.

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• We would like to thank Varian Oncology Systems for providing detailed treatment head designs to simulate a Varian Clinac 2100C accelerator.

ACKNOWLEDGMENTS

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Development of a radiophotoluminescent glass plate detector for small field dosimetry Araki F....

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