Development of a radiophotoluminescent glass plate detector for small field dosimetry
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Transcript of Development of a radiophotoluminescent glass plate detector for small field dosimetry
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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X- axis (mm)
Rel
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GPDXV- IIGAF XREGSnrc
4 MV, 15 mm, depth=5 cm
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- 15 - 10 - 5 0 5 10 15
X- axis (mm)
Rel
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GPDXV- IIGAF XREGSnrc
10 MV, 15 mm, depth=5 cm
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Comparison of dose profiles between GPD and film dosimeters and EGSnrc
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X- axis (mm)
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GPDXV- IIGAF XREGSnrc
4 MV, 9 mm, depth=5 cm
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Rel
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GPDXV- IIGAF XREGSnrc
10 MV, 9 mm, depth=5 cm
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Comparison of dose profiles between GPD and film dosimeters and EGSnrc
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X- axis (mm)
Rel
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GPDXV- IIGAF XREGSnrc
4 MV, 5 mm, depth=5 cm
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X- axis (mm)
Rel
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GPDXV- IIGAF XREGSnrc
10 MV, 5 mm, depth=5 cm
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Comparison of dose profiles between GPD and film dosimeters and EGSnrc
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X- axis (mm)
Rel
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GPDXV- IIGAF XREGSnrc
10 MV, 2 mm, depth=5 cm
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X- axis (mm)
Rel
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GPDXV- IIGAF XREGSnrc
4 MV, 2 mm, depth=5 cm
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Comparison of dose profiles between GPD and film dosimeters and EGSnrc
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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Circular collimator size (mm)
Ou
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Ion chamberSFDGRDDiamondGPDEGSnrc
4 MV
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Circular collimator size (mm)
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Ion chamberSFDGRDDiamondGPDEGSnrc
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Output factors normalized to a 10 x 10 cm2 field
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Circular collimator size (mm)
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Ion chamberSFDGRDDiamondGPDEGSnrc
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Circular collimator size (mm)
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Ion chamberSFDGRDDiamondGPDEGSnrc
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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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