P265] Small field dosimetry comparison of 6 MV beam profiles aquired with diodesrs vs 0.125cc ionization chamber

Abstract

Purpose Compare TPS calculated profiles based on 0.125 cc ionization chamber measurements for linac commissioning with beam profiles acquired using IAEA small beam recommendations with DiodeSRS. Methods At Eclipse™ 11.0 we calculated dose distribution for 2 × 2 cm, 3 × 3 cm and 4 × 4 cm MLC collimated fields at 100 cm SSD with AAA algorithm based on data acquired with 0.125cc PTW ionization chamber. Using TPS dose profile tool, we got the dose values at 10 cm depth. 2 × 2 cm, 3 × 3 cm and 4 × 4 cm MLC collimated field profiles with SSD = 100 cm at 10 cm depth, were acquired following IAEA Technical Reports Series N° 483, in water phantom using DiodeSRS PTW and Mephysto™ mc2 PTW. Transverse beam profiles were compared measuring the full with at half maximum (FWHM). Results For each field, we found a decrease in the FWHM between 2% and 10% for the DiodeSRS measurements. Conclusions Using the IAEA protocol for small field measurements we found that DiodeSRS detectors are more accurate measuring small field relative dosimetry. We intend to recommission our linac small fields according to IAEA report and evaluate the impact on our IMRT/VMAT plans quality assurance.