SU-E-T-73: Investigation of 3D Dosimetry for Proton Therapy Using PRESAGE.

PURPOSE This investigation studies the feasibility of PRESAGE, a 3D polyurethane dosimeter, for relative dosimetry measurements of clinically relevant proton treatments using an anthropomorphic head phantom developed by the Radiological Physics Center (RPC). Performance of a low-LET dependent PRESAGE was evaluated by comparison to the traditionally used radiochromic film, EBT2, and thermoluminescent dosimeters (TLDs). METHODS The head phantom consists of a human skeleton with synthetic isocyanate rubber having similar tissue-equivalent radiological properties to high-energy protons cast around it to mimic natural heterogeneous anatomical structures. The phantom has a cutout that admits either a film and TLD insert or a PRESAGE dosimeter. A treatment plan was developed and delivered twice: once with the film/TLD insert and again with the PRESAGE dosimeter. The 3D dose distribution from the PRESAGE was read out using the Duke medium-field-of-view optical-CT scanner (DMOS). The measured dose distributions were compared to the treatment plan and the distance to agreement (DTA) within the high dose regions was calculated in the sagittal and coronal planes as measured by the EBT2 film. RESULTS PRESAGE dose profiles showed agreement within 3mm and 4mm in the coronal and sagittal planes respectively. Film data showed agreement to 2mm in both planes. A 2D gamma comparison between the PRESAGE and planning data gave 95% agreement with 5%/3mm and 5%/4mm in those respective fields. CONCLUSION PRESAGE dosimeters show great potential for measuring dose distributions from proton fields within heterogeneous volumes, with the opportunity to measure volumetric dose data. Data within the high dose regions of the treatment showed comparable DTAs from two dosimetry systems. With film measurements confirming PRESAGE readings, dose data in low dose regions in clinically sensitive regions can now be better determined. Additional work will include organs at risk (OAR) considerations allowing for detailed DVH comparisons, as well as 3D gamma analysis. NIH grant 5R01CA100835.