Ultra-High Dose-Rate Carbon-Ion Scanning Irradiation with a Compact Type Medical Synchrotron toward FLASH Research

Abstract

<h3>Purpose/Objective(s)</h3> To establish an irradiation system to enable the ultra-high dose-rate (uHDR; FLASH) scanned carbon-ion irradiation with a compact type medical synchrotron. <h3>Materials/Methods</h3> After technical adjustments of the accelerator operation parameters, the medical synchrotron extracted ≥1.0 × 10⁹ carbon-ions (2.0 nC/spill) at 208.3 MeV/u (86 mm in range) within a maximum 100 ms. The uHDR carbon-ion beam delivery system was designed to prevent damage to monitors in the nozzle due to the uHDR beam by avoiding passage through the nozzle. The dose amount was adjusted by the extraction time of the total spill with a function generator. The carbon-ion beam was scanned once to create a field within the extraction time. Advanced Markus chamber and radiographic film were used to measure the absolute dose and the field size respectively, at a plateau depth. Operation voltage of the chamber was set to 400 V at the uHDR. <h3>Results</h3> The FLASH irradiation utilizing beam scanning was confirmed with a dose of 5.4 Gy (homogeneity of ±2%) for the beam in a volume of at least 16 mm × 16 mm in a square field and a corresponding dose-rate of 95 Gy/s (± 1%). The dose was changed to about 0.7, 1.5, 2.9 Gy for the dose-rate and the field size. Details of the results are shown in Table1. <h3>Conclusion</h3> The FLASH dose-rates >40 Gy/s at different dose levels were achieved in a useful field size for research created by the scanned carbon-ion beams with the compact type medical synchrotron. This study reported promising beam characteristics of uHDR scanned carbon-ion beams, at different dose levels, and can be used for further investigation of carbon-ion FLASH research. The dose and dose-rate established with the uHDR irradiation system can be applied in biological experiments.