Design of a Synchrotron for Proton FLASH Radiotherapy Based on Fast Variable-Energy Bunch Splitting

Ultra-high dose rate (FLASH) radiotherapy not only guarantees effective tumor treatment but also greatly enhances the protection of normal tissue. Moreover, it is a convenient procedure for tumor patients that has enhanced the benefits provided by medical institutions. Proton FLASH radiotherapy, which combines the Bragg peak effect of proton spatial dose distribution with the unique temporal effect advantage of FLASH, is an attractive tumor treatment approach. To achieve proton FLASH discrete pencil beam scanning in a 1-L volume, taking into account the 5-mm point interval, 9261 points would need to be irradiated within 500 ms, which is beyond the capability of existing medical devices. To meet these requirements, based on a fast cycle synchrotron with a period of 25 Hz, we simultaneously combined variable-energy, fast splitting, and extraction beam bunches, and proposed a scanning method suitable for continuous variable-energy extraction bunches. The proposed technique meet the requirements of proton FLASH discrete pencil beam scanning within a volume of 1 L.