Session Item

The accuracy of dose delivery in the preclinical small animal image-guided (SA-IGRT) systems depends on a number of operator- and system-related factors that can individually or cumulatively contribute to significant dosimetric errors. Aim of this work is to initiate an independent dose verification technique using electronic portal imaging device (EPID) to verify the delivered dose to small animal during radiation therapy.

We calibrated a camera-based EPID on the small animal radiation research platform (SARRP, Xstrahl, Inc.) to measure transit dose at the imager plane. Transit dose was back-projected at object’s exit surface to determine exit dose. First, we validated developed EPID dosimetry technique against film measurements through homogeneous and heterogeneous phantoms. Second, we implemented this technique in administered image-guided radiotherapy fraction for 20 rats with prostate cancer. We compared the planned dose distributions calculated by the treatment planning system (TPS) with delivered dose measured by the EPID.

Transit central axis dose values measured with the EPID showed close agreement with film measurements, differences were within 4.9%. For inhomogeneous phantom, the EPID and film exit dose measurements agreed within ≤2%. For animal study, average difference between TPS and EPID was 3%, with a maximum of 9.3%. Gamma analyses for exit dose verification between TPS-calculated and EPID-measured dose distributions showed average 90% passing rate under global 2mm/5% gamma criteria.

We implemented a kilovoltage EPID dosimetry technique to verify accuracy of SA-IGRT to improve fidelity of preclinical radiation research. Beyond the current scope, we expect that this framework may be applied to any SA-IGRT system that incorporates an EPID.