A Xu¹*, H Lin², C Chen², Y Wang¹, J Adamovics³, C Wuu¹, (1) New York Presbyterian/Columbia University Irving Medical Center, New York, NY, (2) New York Proton Center, New York, AA, (3) HEURIS, INC., Skillman, NJ

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  A Xu

PO-GePV-T-92 (Sunday, 7/25/2021)   [Eastern Time (GMT-4)]

Purpose: To evaluate the energy and dose rate dependence of the PRESAGE response for the application of the 3D dosimeters to Proton therapy dosimetry.

Methods: Measurements were made using 4 PRESAGE dosimeters of 10 cm diameter and 10 cm length. Each phantom was setup at a 226-cm SSD and irradiated using 4 single-spot proton pencil beams with intended maximum doses around 1 Gy, 3 Gy, 5 Gy and 10 Gy using Varian ProBeam system. Proton pencil beams with 2 energies (100 MeV and 70 MeV) and 2 dose rates (700 nA and 350 nA Cyclotron currents) were used. The irradiated phantoms were scanned using a newly designed broad-beam optical CT scanner that utilizes fiber optic taper for collimation of transmitted lights. The scanning time for each phantom is about 10 minutes with 1 mm resolution. Dose response curves were generated from each phantom along the central axes of the pencil beams at 3 different depths and analyzed for the energy dependence and the dose rate dependence. Three-dimensional comparisons were also made between the dose distributions from the measurements and the treatment planning system.

Results: The measured Bragg peak depths for the 100 MeV and 70 MeV beams are 70 mm and 38.0 mm, compared with 75.3 mm and 40.3 mm in water, respectively. The measured water-equivalent thickness is 1.07 which is comparable with the physical density of PRESAGE (1.07 gm/cm3). No energy and dose rate dependence was observed for this PRESAGE formula within the accuracy of the experimental approach. The measured central depth dose curve for each energy agrees well with the planning system for small depths but is in general 10-35% lower than the plan in the Bragg peak region.

Conclusion: Preliminary results indicate that the Presage dosimeters can be used for proton therapy dosimetry with adequate corrections for the physical density of the dosimeters and the dose quenching effect.

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