SU‐F‐J‐14: Kilovoltage Cone‐Beam CT Dose Estimation of Varian On‐Board Imager Using GMctdospp Monte Carlo Framework

Abstract

Purpose:Although cone‐beam CT (CBCT) imaging became popular in radiation oncology, its imaging dose estimation is still challenging. The goal of this study is to assess the kilovoltage CBCT doses using GMctdospp ‐ an EGSnrc based Monte Carlo (MC) framework.Methods:Two Varian OBI x‐ray tube models were implemented in the GMctpdospp framework of EGSnrc MC System. The x‐ray spectrum of 125 kVp CBCT beam was acquired from an EGSnrc/BEAMnrc simulation and validated with IPEM report 78. Then, the spectrum was utilized as an input spectrum in GMctdospp dose calculations. Both full and half bowtie pre‐filters of the OBI system were created by using egs_prism module. The x‐ray tube MC models were verified by comparing calculated dosimetric profiles (lateral and depth) to ion chamber measurements for a static x‐ray beam irradiation to a cuboid water phantom. An abdominal CBCT imaging doses was simulated in GMctdospp framework using a 5‐year‐old anthropomorphic phantom. The organ doses and effective dose (ED) from the framework were assessed and compared to the MOSFET measurements and convolution/superposition dose calculations.Results:The lateral and depth dose profiles in the water cuboid phantom were well matched within 6% except a few areas ‐ left shoulder of the half bowtie lateral profile and surface of water phantom. The organ doses and ED from the MC framework were found to be closer to MOSFET measurements and CS calculations within 2 cGy and 5 mSv respectively.Conclusion:This study implemented and validated the Varian OBI x‐ray tube models in the GMctdospp MC framework using a cuboid water phantom and CBCT imaging doses were also evaluated in a 5‐year‐old anthropomorphic phantom. In future study, various CBCT imaging protocols will be implemented and validated and consequently patient CT images will be used to estimate the CBCT imaging doses in patients.