Implementation of ultra-high dose-rate electron beam from 6-MeV C-band linear accelerator for preclinical study

Recent biological studies with ultra-high dose-rate (> 40 Gy/s) irradiation demonstrate the killing of tumors along with a reduction in the side-effect on normal tissues. These features can suggest the alternative radiotherapy method. The radio-biological mechanisms need to be understood, and to be applied tumor treatment. Biological validations of the ultra-high dose-rate beam are required. The 6-MeV electron linear accelerator constructed in 2015 at the Dongnam Institute of Radiological & Medical Sciences was upgraded to generate an electron beam at an ultra-high dose rate and to provide preclinical irradiation for in vitro studies of cells and small animals. The irradiation device was designed with a dual scattering foil system to achieve a uniform beam distribution with a diameter of 30 mm at a distance of 110 mm from the primary foil. The 6-MeV accelerator operating with a 6-MW pulse modulator based on a thyratron-switched pulse-forming network provides beam operation per pulse utilizing a single-board computer to control the pulse timing. The film dosimetry at a depth of 10 mm in a water phantom of the irradiation device demonstrated that a beam with an RF power of 2.5 MW and an electron-gun heating current of 2 A produced a dose per pulse of 4.22 +/- 0.12 Gy/pulse. This resulted in a dose rate of 422 Gy/s with a pulse rate of 100 Hz. The upgraded accelerator was successfully tested for preclinical use and is currently in full operation with studies being performed on the radio-biological effects of ultra-high dose-rate beam. The paper describes the design features of the ultra-high dose-rate electron beam generated from the 6-MeV accelerator and the dose measurement using the irradiation device. The design of the preclinical irradiator is also discussed.