Identification of a 3D dosimeter best-suited for use by the RPC

M. Heard, G. Ibbott, D. Followill, R. White, E. Jackson, M. Salehpour

Motivation

• RPC has a family of anthropomorphic phantoms

• Phantoms use TLD and film

• Radiation treatments are 3D

• A 3D dosimeter is needed

Which 3D dosimeters?

• There are many 3D formulations to choose from– BANG®, MAGIC, MAGAT, PAGAT, VIPAR,

PRESAGE™, etc.

Purpose

Characterize several different 3D dosimeters and identify one best-suited for the RPC’s needs.

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.

• 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

• 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

• 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

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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Dose (Gy)

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Dose response of PAGAT imaged with OCT. Error bars represent one standard deviation.

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Dose resolution of PAGAT imaged with OCT

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Distance from central axis (mm)

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# 5 # 7 # 1

PRESAGE™ irradiated to 8.25 Gy using a half blocked field

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PRESAGE™ irradiated to 8.25 Gy using a half blocked field

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PRESAGE™ irradiated to 2 Gy using a half blocked field

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

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

Thank You