Preclinical Ultra-High Dose Rate (FLASH) Proton Radiation Therapy System for Small Animal Studies

Abstract

BackgroundAnimal studies with ultra-high dose-rate radiation therapy (FLASH, >40Gy/s) preferentially spare normal tissues without sacrificing anti-tumor efficacy compared to conventional dose-rate radiation therapy (CONV). At XXXX, we developed a cyclotron-generated preclinical scattered proton beam with FLASH dose rates. We present the technical details of our FLASH radiation system and preliminary biological results from whole pelvis radiation. MethodsA Scanditronix MC50 compact cyclotron beamline has been modified to produce a 48.7 MeV proton beam at dose rates between 0.1-150 Gy/s. The system produces a 6 cm diameter scattered proton beam (flat to +/-3%) at the target location. Female C57BL/6 mice 5-6 weeks old were used for all experiments. To study normal tissue effects in the distal colon, mice were irradiated using the entrance region of the proton beam to the whole pelvis, 18.5 Gy at different dose rates: control, CONV (0.6–1 Gy/s) and FLASH (50–80 Gy/s). Survival was monitored daily and EdU (5-ethynyl-2´-deoxyuridine) staining was performed at 24-hours and 96-hours post-radiation. Cleaved caspase-3 (C-CASP3) staining was performed 24-hours post-radiation. To study tumor control, allograft B16F10 tumors were implanted in the right flank and received 18 Gy CONV or FLASH proton radiation. Tumor growth and survival were monitored. ResultsAfter 18.5 Gy whole pelvis radiation, survival was 100% in the control group, 0% in the CONV group, and 44% in the FLASH group (p<0.01). EdU staining showed cell proliferation was significantly higher in the FLASH versus CONV group at both 24-hours and 96-hours post-radiation in the distal colon, although both radiation groups showed decreased proliferation compared to controls (P<0.05). Lower C-CASP3 staining was seen in the FLASH versus conventional group post-radiation (p<0.05). Comparable flank tumor control was observed in the CONV and FLASH groups. ConclusionWe present our preclinical FLASH proton radiation system and biological results showing improved survival after whole pelvis radiation, with equivalent tumor control.