Image guided IMRT dosimetry using anatomy specific MOSFET configurations

Abstract

We have investigated the feasibility of using a set of multiple MOSFETs in conjunction with mobileMOSFETâ wireless dosimetry system, to perform a comprehensive and efficient quality assurance (QA) of IMRT plans. Anatomy specific MOSFET configurations incorporating 5 MOSFETs, have been developed for a specially designed IMRT dosimetry phantom. Kilovoltage cone beam computed tomography (kV CBCT) imaging was used to increase the positional precision and accuracy of the detectors and phantom, and so minimize dosimetric uncertainties in high dose gradient regions. The effectiveness of the MOSFET based dose measurements was evaluated by comparing the corresponding doses measured by an ion chamber. For 20 Head and Neck IMRT plans the agreement between the MOSFET and ionization chamber dose measurements was found to be within (-0.26±0.88)% and (0.06±1.94)% (1s) for measurement points in the high dose and avoiding volumes respectively. A 1 mm precision for the phantom positioning was achieved by using the X-Ray Volume Imaging (XVI) kV CBCT system available with the Elekta Synergyâ Linear Accelerator. Using the anatomy specific MOSFET configurations, simultaneous measurements were made at five strategically located points covering high dose and avoidance regions. The agreement between measurements and calculated doses by the TPS for Head & Neck and prostate IMRT plans was found to be within (0.47±2.45)%. The results indicate that anatomy specific phantom modules incorporating multiple MOSFETS, in conjunction with image guidance, can be utilized to perform a comprehensive and efficient quality assurance of IMRT plans.