TH‐C‐T‐6E‐04: Evaluation of a New 3D Polyurethane Dosimeter for IMRT Verification

Purpose: To demonstrate the dosimetric accuracy of PRESAGE™, a new type of three‐dimensional dosimeter, when used in the Radiological Physics Center's (RPC) Head and Neck Phantom. Method and Materials: An IMRT treatment plan was developed for the RPC Head and Neck Phantom, which contained simulated planning target volumes and an organ at risk. A conventional dosimetry insert, containing radiochromic film and TLD, was in place while the IMRT plan was delivered. The insert was removed and replaced with a PRESAGE™ dosimeter and delivery of the IMRT plan was repeated. An additional PRESAGE™ dosimeter was irradiated to doses between 0.5 and 7.5 Gy with stereotactic beams to develop a calibration curve. The PRESAGE™ dosimeter was imaged using an OCT‐OPUS™ laser CT scanner 24 hours after irradiation. Two‐dimensional comparisons were performed between the treatment plan, the distribution measured with film/TLD and the distribution measured with PRESAGE™. Results: The PRESAGE™ dosimeter showed a monotonic and easily characterized response with dose. Optical density maps obtained following IMRT delivery were converted to dose and compared with the treatment plan and with film/TLD data. Film and PRESAGE™ data showed good agreement, and both indicated higher doses in the steep gradient region between the PTV and the organ at risk. Conclusion: This work demonstrated the use of PRESAGE™ as a dosimetric tool for the verification of IMRT treatments. The dosimeter provided a three‐dimensional distribution that was used for comparisons with treatment plan distributions. The investigation was supported by PHS grants CA 10953 and CA81647 awarded by the NCI, DHHS.