identification of a 3d dosimeter best-suited for use by the rpc m. heard, g. ibbott, d. followill,...
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Identification of a 3D dosimeter best-suited for use by the RPC
M. Heard, G. Ibbott, D. Followill, R. White, E. Jackson, M. Salehpour
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Motivation
• RPC has a family of anthropomorphic phantoms
• Phantoms use TLD and film
• Radiation treatments are 3D
• A 3D dosimeter is needed
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Which 3D dosimeters?
• There are many 3D formulations to choose from– BANG®, MAGIC, MAGAT, PAGAT, VIPAR,
PRESAGE™, etc.
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Purpose
Characterize several different 3D dosimeters and identify one best-suited for the RPC’s needs.
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3D Formulations Investigated• PAGAT (polymer gel) 1
– manufactured in-house
• BANGkit™ (polymer gel) 2
– Supplied by MGS Research Inc.
• PRESAGE™ (radiochromic dosimeter) 3
– Supplied by Heuris Pharma
1 Venning, A.J., et al., Investigation of the PAGAT polymer gel dosimeter using magnetic resonance imaging. Physics in Medicine & Biology, 2005. 50(16): p. 3875-88.
2 Murakami, Y., et al., Evaluation of the basic properties of the BANGkit™ gel dosimeter. Phys. Med. Biol., 2007. 52(8): p. 2301-2311.
3 Adamovics, J. A. and M.J. Maryanksi, Characterisation of PRESAGE™: A new 3-D radiochromic solid polymer dosemeter for ionising radiation. Radiation Protection Dosimetry, 2006.
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• Polymer Gels– Made of water, gelatin, and monomers– Irradiation initiated polymerization process– Polymers change the optical turbidity and relaxation
properties of the gel
• PRESAGE™– Composed of a polyurethane matrix doped with leuco
dye– Dosimeters are optically clear before irradiation– Irradiation causes exposed areas to turn blue
Unirradiated Irradiated
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• Determined the dose response up to 10 Gy using 6 MV photons for 3 batches of each formulation
• Determined the dose resolution and inter-batch reproducibility
2 Gy 5 Gy 10 GyPAGAT dosimeters irradiated to different doses
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• A half-blocked field was used to irradiate a batch of each formulation
• Doses of 2 Gy, 5 Gy, and 8.25 Gy were delivered– Multiple dosimeters irradiated at each dose
level
• Radiochromic film also irradiated using a half-blocked field
• Determined the dosimetric accuracy, spatial accuracy, and intra-batch reproducibility
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Imaging
• PRESAGE™ dosimeters imaged with optical CT
• Polymer gels were imaged with optical CT and MRI
Bruker 4.7T scannerOptical CT system
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0
10000
20000
30000
40000
50000
60000
0 1 2 3 4 5 6 7 8
Dose (Gy)
Ne
t O
D (
arb
itra
ry u
nit
s)
Group A Group B Group C
Dose response of PAGAT imaged with OCT. Error bars represent one standard deviation.
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0.00
0.05
0.10
0.15
0.20
0 1 2 3 4 5 6 7 8
Dose (Gy)
DD
95%
(G
y)
Group A Group B Group C
Dose resolution of PAGAT imaged with OCT
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0
2000
4000
6000
8000
10000
12000
14000
-15 -10 -5 0 5 10 15
Distance from central axis (mm)
Ne
t O
D (
arb
itra
ry u
nit
s)
# 5 # 7 # 1
PRESAGE™ irradiated to 8.25 Gy using a half blocked field
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0
0.2
0.4
0.6
0.8
1
1.2
-15 -10 -5 0 5 10 15
Distance from central axis (mm)
No
rmal
ize
d D
ose
# 5 # 7 # 1 Film
PRESAGE™ irradiated to 8.25 Gy using a half blocked field
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0.0
0.2
0.4
0.6
0.8
1.0
1.2
-15 -10 -5 0 5 10 15
Distance from central axis (mm)
No
rmal
ize
d D
ose
# 2 # 9 # 10 Film
PRESAGE™ irradiated to 2 Gy using a half blocked field
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Characteristics Evaluated
1. Dosimetric accuracy
2. Dose resolution
3. Cost
4. Intra-batch reproducibility
5. Monotonic dose response
6. Spatial accuracy
7. Linear dose response
8. Inter-batch reproducibility
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Summary
• Dose response differs by more than 4% between batches of each 3D dosimeter formulation
• Intra-batch reproducibility > 2% for all dosimetry systems
• OCT system resulted in inaccuracies at low OD
• PAGAT polymer gel with OCT imaging was selected as the dosimetry system to be tested in the RPC’s phantoms
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Thank You