SU-E-T-136: Measure the Actual Radiation Dose Delivered for Prostate IMRT Treatment Using An Implantable MOSFET Dosimeter

Abstract

Purpose: To report the initial clinical experience using an in‐vivo, implantable metal oxide semiconductors field effect transistors(MOSFET)dosimeters for the daily dose verification of prostate IMRTtreatment.Methods: The dose verification system (DVS) from Sicel Technologies was used to measure the actual dose delivered for prostate IMRT patients. Fifteen patients (10 prostate IMRT; 5 Sequential IMRT, pelvis then prostate) were implanted with two DVS dosimeters in the prostate gland: one on the right and the other on the left. The location of the DVS dosimeters were identified on the CTimages and the expected doses were calculated. The measured readings of the dosimeters were compared to the expected dose values. Daily orthogonal portal film or CBCT was used for patient setup.Results: The average difference between predicted and measured doses was 1.1% for all 15 patients (30 dosimeters) over the whole course of treatment. The range of the difference between the measured cumulative doses to the planned doses for the whole treatment course was from −5.3% to 5.1%. For three out of fifteen patients, a new plan was created as the measured doses disagreed with the expected value for the original plans. For those three patients, the difference between measured and the predicted doses was as large as 11.3%. The discrepancies were much smaller after replanning. The average dosimeter measurement for the nine prostate IMRTtreatment (exclude one prostate IMRT patient who had been re‐planned) over the course of treatment was decreasing signifying a possible decrease in the sensitivity of the dosimeters Conclusions: This study demonstrated DVS dosimeters could provide valuable information about actual dose delivered and actual dose fluctuations of the daily treatment. The DVS dosimeters could serve as a patient specific quality assurance and guidance for adaptive radiation therapy.