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Measurement of Proton-Activated Positron Emission with PRESAGE 3-D Dosimeters

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M Carroll

M Carroll1*, J Adamovics2 , O Mawlawi1 , G Ibbott1 , (1) University of Texas MD Anderson Cancer Center, Houston, TX, (2) John Adamovics, Skillman, NJ


SU-E-T-230 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Measurement of positron emission following proton beam irradiation of a target has been studied as a method of in-vivo dosimetry. Relative dosimetry studies between a phantom and treatment plan are susceptible to range uncertainties from material heterogeneities and setup error. By using the radiochromic polyurethane dosimeter PRESAGE, we can correlate the proton dose distribution to the PET activity measurement within a single detector. The PRESAGE formulation used was developed for high-LET proton radiotherapy, has similar density and RLSP to tissue, and consists of a greater carbon component, which gives it a higher positron signal than many other 3D detectors.

Three cylindrical PRESAGE dosimeters were irradiated semi-uniformly to 500 cGy with 180-MeV protons. The beam was directed along the dosimeter axis and delivered a 2-cm SOBP at the center of the dosimeter. The dosimeters were rushed to a nearby PET/CT where imaging began within 15 minutes, less than a single half-life of 11C. A 3-hr measurement captured the full activation decay. Afterwards, the dose profiles were measured by optical-CT. A direct comparison between the measured dose and the positron emission was performed using CERR software.

The correlations between dose distributions and PET activity were consistent with previous studies in that the proximal region of the SOBP displayed the highest activity. The spatial distributions between the dose and activity were similar. Along the central axis of the beam, we found a shift in the distal 80% of 1 cm. The lateral profile showed good agreement between dose and activity. PET imaging times between 30-min and 3-hrs showed <5% discrepancy.

PRESAGE dosimeters offer a strong and unique potential to accurately correlate dosimetric and PET activation information. Implementation in an anthropomorphic phantom could be used to study representative treatment plans.

Funding Support, Disclosures, and Conflict of Interest: NIH grant 5R01CA100835

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