Room: Exhibit Hall | Forum 2
Purpose: The use of kilovoltage cone-beam computed tomography (CBCT) for daily patient imaging is increasing in the field of proton therapy. The purpose of this work was to characterize beam output and organ doses from a proton gantry-mounted CBCT system with two different Monte Carlo codes and to evaluate the performance of both codes.
Methods: The Monte Carlo codes MCNP6 and GATE were used to model a kV-CBCT tube installed at a clinical proton therapy facility. Both codes were benchmarked against measurements with regard to central-axis depth dose curves in water and spatial profiles in air for imaging with a head, thorax and pelvis protocol employing tube voltages between 100-120 kV using full-fan acquisition. Full rotation patient imaging was then simulated on CT geometry of an adult whole-body phantom scoring energy deposition in three-dimensional grids. The output was used to calculate normalized organ absorbed doses and dose-volume histograms (DVH) for inter-comparison between the codes.
Results: Depth dose curves from measurements and simulations agreed within 3.5% for all protocols. The corresponding agreement of beam profiles in air was 4.3% (FWHM). The average agreement between MCNP6 and GATE in normalized absorbed doses from patient imaging for organs located inside the imaging field was 3%, 7% and 4% for the head, thorax and pelvis protocols, respectively. For organs located partly inside the imaging field, the average difference increased to approximately 10-15% for all protocols. In accordance with previous findings, both codes produced DVH with an increase in maximum dose to bone tissues in comparison to soft tissues for all protocols.
Conclusion: Simulations of a kV-CBCT system with MCNP6 and GATE showed good agreement with regard to beam characteristics and organ DVH. These findings will be useful in future studies on the total dose burden for patients undergoing proton therapy and CBCT imaging.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the Swedish Radiation Safety Authority under the contract SSM2017-2379