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Study of water equivalence of the PRESAGE dosimeter for 3D
proton beam dosimetry
1 Institute of Medical Physics, School of Physics, University of Sydney, NSW 2006,Australia
2 Department of Radiation Oncology, Royal Prince Alfred Hospital, Sydney, NSW 2050,Australia
Tina Gorjiara1, Zdenka Kuncic1 , Robin Hill1, 2 Samuel Blake1 and Clive Baldock1
History of Proton Therapy
› Dr Robert Wilson (1914-2000)- A Harvard University physicist who played a
central role on the development of the atomicbomb
- Published a paper in 1946 that first proposed themedical use of protons for cancer therapy
› In 1954- The University of Berkeley began using proton
technology after the construction of a cyclotron totreat cancer patient
Proton therapy
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Dosimetry in proton therapy› According to IAEA recommendations, the dosimetry of proton beams can
be performed with an ionization chamber dosimeter .
› However, because of the steep dose gradients, dose measurements aredifficult close to the Bragg peak.
› In addition, the ion chambers only provide point dose information andwould require a large number of them to provide two or three dimensionaldosimetric information.
› Therefore, 3D dosimetry techniques such as polymer gel dosimetry haspotential to be used as dosimeters to improve spatial resolution in protontherapy dosimetry.
Gel Dosimetry5
a) b) c)
d) e) f)
What is PRESAGE?
› The PRESAGE dosimeter is composed of radiochromiccomponents (leuco dyes) and halogen-containing freeradical initiators.
› It undergoes a color change when exposed to ionizingradiation.
Advantages of PRESAGE as a dosimeter
› Being able to provide three-dimensional dose information.
› Insensitivity to oxygen contamination.
› Being machinable and molded to variety of shapes andsizes.
› Absorbing rather than scattering light which facilitates highaccuracy readout by optical CT.
Different formulations of PRESAGE
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Material
Effective
atomic
number
Density
(g/cm³)wH wC wN wO wS wCl wBr
PRESAGE®
Formulation A7.69 1.050 0.089 0.62 0.050 0.21 0.0038 0.031 0.0023
PRESAGE®
Formulation B7.74 1.050 0.091 0.62 0.049 0.21 0.019 0.0021 0.0047
PRESAGE®
Formulation C8.65 1.101 0.089 0.61 0.045 0.22 - 0.033 0.0084
PRESAGETM 9.70 1.112 0.090 0.61 0.045 0.22 - 0.023 0.018
Water 7.42 1.000 0.11 - - 0.89 - -
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Aim
› Since Monte Carlo simulations can provide accuratepredictions of dose (GOLD STANDARD) , in this work, wehave calculated the relative dose response of the fourPRESAGE dosimeters to proton beam and compared it withdose response of water.
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Method
› The GEANT4 Hadrontherapy example was modified accordingly tocalculate depth doses in the PRESAGE® Formulation A, PRESAGE®Formulation B, PRESAGE® Formulation C, PRESAGETM and water.
› Mean energy of proton beam was set to 62 MeV.
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Method
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40 cm
40 cm
Method
› To compare the depth doses in each dosiemeter, the water equivalentthickness (WET) was calculated according to IAEA technical report 398 foreach dosimeter using the following formula:
› tm is thickness of dosimeters and Rw and Rm are the proton range inwater and PRESAGE dosimeter, respectively.
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m
wm R
RtWET ≈
Results
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Results
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Results
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Results
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Results
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Results
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Results
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Results
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Results
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Results
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0
1000
2000
3000
4000
5000
6000
7000
8000
0 0.5 1 1.5 2 2.5 3 3.5
Dep
osite
d en
ergy
(MeV
)
Water equivalent thickness (cm)
Secendary protons
PRESAGE® Formulation AWater
Results
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0.5
1
1.5
2
2.5
3
3.5
0 0.5 1 1.5 2 2.5 3 3.5
Dep
osite
d en
ergy
(MeV
)
Water equivalent thickness (cm)
Secendary Neutrons
PRESAGE® Formulation AWater
Results
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0
5000
10000
15000
20000
0 0.5 1 1.5 2 2.5 3 3.5
Dep
osite
d en
ergy
(MeV
)
Water equivalent thickness (cm)
Secondary electrons
PRESAGE® Formulation A
Water
Conclusion
› PRESAGE® dosimeters with new formulas, specially formulation A, are
more water equivalent than the currently available PRESAGE dosimeter.
› Thus more suitable for accurate 3D dosimetry of proton beams.
› Further experimental studies are planned to investigate possible saturation
in PRESAGE for high LET radiation fields.
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Thanks!
