PHITS-DCHAIN을 이용한 양성자치료 사이클로트론 방사화 및 감마선속 평가

Evaluation of Cyclotron Activation and Gamma Flux in Proton Therapy Using PHITS-DCHAIN

The global demand for proton therapy has been increasing across various medical institutions dueto advantages such as the Bragg peak effect. Currently, cyclotron-based proton therapy systems are widely usedin medical institutions. However, during proton acceleration, a certain level of beam loss is inevitable inside thecyclotron, resulting in activation phenomena. Therefore, assessing activation within the cyclotron is crucial duringmaintenance work or component disposal. This study aims to evaluate the activation and gamma flux in protontherapy cyclotron components after operation cessation, considering cooling time, using the PHITS computationalcode. To accomplish this, the reliability of the PHITS code was verified, a cyclotron model was implemented inPHITS for simulation, and activation and gamma flux were calculated using the DCHAIN tally. First, the reliabilityof the PHITS computational code was verified by comparing the proton range in water obtained from PHITS withexperimental data provided by international organization. The cyclotron modeling was based on the SC cyclotron,which serves as a reference model for proton therapy cyclotrons, and activation evaluations were conductedaccordingly. Finally, changes in radioactivity and gamma flux according to the cooling time after cyclotron shutdownwere assessed. The reliability verification demonstrated that the differences between the PHITS results and thosereported by international organizations were all within 1%. The activation evaluation using the DCHAIN tallyindicated that the highest activation occurred in the beam extraction component, where protons directly collide. Additionally, in the Dee, where activation is primarily induced by neutrons, the most significant decay occurred withincreasing cooling time after beam termination. Moreover, copper-based components, including the beam extraction,Dee, and superconducting coil, exhibited significant reductions in radioactivity and gamma flux over time. In contrast,iron-based components, such as the cryostat, iron hill, and iron yoke, showed a decay of approximately twice theinitial value even after 48 hours. The findings of this study can serve as valuable references for developing guidelineson future maintenance and component disposal.

The global demand for proton therapy has been increasing across various medical institutions dueto advantages such as the Bragg peak effect. Currently, cyclotron-based proton therapy systems are widely usedin medical institutions. However, during proton acceleration, a certain level of beam loss is inevitable inside thecyclotron, resulting in activation phenomena. Therefore, assessing activation within the cyclotron is crucial duringmaintenance work or component disposal. This study aims to evaluate the activation and gamma flux in protontherapy cyclotron components after operation cessation, considering cooling time, using the PHITS computationalcode. To accomplish this, the reliability of the PHITS code was verified, a cyclotron model was implemented inPHITS for simulation, and activation and gamma flux were calculated using the DCHAIN tally. First, the reliabilityof the PHITS computational code was verified by comparing the proton range in water obtained from PHITS withexperimental data provided by international organization. The cyclotron modeling was based on the SC cyclotron,which serves as a reference model for proton therapy cyclotrons, and activation evaluations were conductedaccordingly. Finally, changes in radioactivity and gamma flux according to the cooling time after cyclotron shutdownwere assessed. The reliability verification demonstrated that the differences between the PHITS results and thosereported by international organizations were all within 1%. The activation evaluation using the DCHAIN tallyindicated that the highest activation occurred in the beam extraction component, where protons directly collide. Additionally, in the Dee, where activation is primarily induced by neutrons, the most significant decay occurred withincreasing cooling time after beam termination. Moreover, copper-based components, including the beam extraction,Dee, and superconducting coil, exhibited significant reductions in radioactivity and gamma flux over time. In contrast,iron-based components, such as the cryostat, iron hill, and iron yoke, showed a decay of approximately twice theinitial value even after 48 hours. The findings of this study can serve as valuable references for developing guidelineson future maintenance and component disposal.