SU-E-T-363: Investigation of PRESAGE® Dosimeters for Proton Therapy

Abstract

Purpose: To evaluate a formulation of PRESAGE® intended for proton therapy and to use it to compare measurements with calculations for a spot scanning pencil proton beam and a passively scattered proton beam.Methods: Two 7.5 cm high by 9.5 cm diameter cylindrical PRESAGE® dosimeters were used. CTimages were used to design two treatment plans with an Eclipse treatment planning system (TPS). The first plan used a single pencil beam of energy 153.2 MeV to provide a range of 16 cm in water. Four regions of the dosimeter were irradiated delivering doses in the peak of approximately 6, 10, 13 and 19 Gy(RBE) by rotating the dosimeter between spot deliveries. The second plan used a single passively scattered field with a spread out Bragg peak (SOBP) of 4 cm. This plan delivered approximately 10 Gy(RBE). The dosimeters were analyzed using an optical CT scanner. The measured optical densities were converted to dose via a calibration curve, exported to the CERR environment and fused to the treatment plan. Dose distributions were scaled to the SOBP plan. Dose profiles were taken along the axis of each spot and the SOBP and perpendicularly across the SOBP.Results: The dose measured in the peak of single spot irradiations increased proportionally to the MU setting. The distal falloff was steeper than predicted by the TPS. The cross profiles for the SOBP plan matched within 2 mm with the TPS. The depth profile was noisy within the modulated area. Noise decreased as dose increased for both dosimeters Conclusions: This formulation of PRESAGE® shows promise as a 3D dosimeter for proton therapy. A dose calibration specific to protons will facilitate further analysis and enable measurement of complex distributions. Work supported by PHS CA010953 and CA081647, awarded by NCI, DHHS.