Optimization and evaluation of multiple gating beam delivery in a synchrotron-based proton beam scanning system using a real-time imaging technique

• We have developed a new function to improve the gated irradiation efficiency.
• The mean irradiation efficiency was improved by about 21%.
• Irradiation time has been shorter than that of conventional case.
• The multiple gated-irradiation function is essential to reduce treatment times.

PurposeTo find the optimum parameter of a new beam control function installed in a synchrotron-based proton therapy system.MethodsA function enabling multiple gated irradiation in the flat top phase has been installed in a real-time-image gated proton beam therapy (RGPT) system. This function is realized by a waiting timer that monitors the elapsed time from the last gate-off signal in the flat top phase. The gated irradiation efficiency depends on the timer value, Tw. To find the optimum Tw value, gated irradiation efficiency was evaluated for each configurable Tw value. 271 gate signal data sets from 58 patients were used for the simulation.ResultsThe highest mean efficiency 0.52 was obtained in TW = 0.2 s. The irradiation efficiency was approximately 21% higher than at TW = 0 s, which corresponds to ordinary synchrotron operation. The irradiation efficiency was improved in 154 (57%) of the 271 cases. The irradiation efficiency was reduced in 117 cases because the TW value was insufficient or the function introduced an unutilized wait time for the next gate-on signal in the flat top phase. In the actual treatment of a patient with a hepatic tumor at Tw = 0.2 s, 4.48 GyE irradiation was completed within 250 s. In contrast, the treatment time of ordinary synchrotron operation was estimated to be 420 s.ConclusionsThe results suggest that the multiple gated-irradiation function has potential to improve the gated irradiation efficiency and to reduce the treatment time.