SU-FF-T-261: Image Guided High Definition Dosimetry of IMRT Plans Using the MobileMOSFET System

Abstract

Purpose: To investigate the feasibility of using multiple MOSFETsensors, available with the mobileMOSFET® system as high definition dosimeter for IMRT plan verification. Methods and Material: Wireless dosimetry system (mobileMOSFET from Thomson Nielsen) was first tested for reproducibility, linearity, sensitivity, long‐term performance, and angular dependency. Twenty head and neck plans, each consisting of 8–10 treatment fields were verified. Plans were generated in Pinnacle 7.6C, and exported to a cylindrical solid water phantom. The in‐phantom dose distribution was calculated on the phantom CTimage set, and two regions of interest were selected: GTV area and avoiding area. The doses at these points were measured using MOSFETs and compared to ionization chamber measurements and Pinnacle calculations. Site specific fixed configurations of 5 MOSFET positions has been developed, and ten patient plans were verified using this module. CBCTimage guidance was used to accurately position the MOSFET phantom. Results: The response of MOSFET was found to be linear, reproducible (within ±2%), independent of angular positions (within ±2%) and stable with time. For 20 head and neck patients, average variations of (0.68±2.11)% at high dose point and (0.06±1.94)% at low dose point were observed between measured dose using MOSFET and ionization chamber. Average variations of (0.73±1.85)% and (0.96±2.00)% were observed between measured dose using MOSFET and plan dose at high and low dose points respectively. A (0.47±2.45)% variation was observed using the special insert for head and neck and prostate plans in four points out of five. Conclusions: These investigations indicate that the use of mobileMOSFET device with image guidance would be suitable for efficient and high‐resolution dose verification of complex IMRT plans.