Room: Track 3
Purpose: evaluate the feasibility and benefit of Flash proton beam scanning therapy on the mouse model of radiation induce skin fibrosis and muscle atrophy using a clinical gantry
Methods: a pencil beam scanning nozzle, a uniform physical dose of 35Gy was delivered to mice rear right hind limb with a collimated 2.5x2.5cm field. Irradiations were on the plateau region of a 250 MeV single layer field at various dose rates:(n=8 mice/group): Sham, Conventional (Conv, 1.4Gy/s), Flash60 (57.3Gy/s), Flash115 (115.0Gy/s) or splitFlash60 (2x17.5Gy at 57.4Gy/sec with 1min30sec interval between fractions). Acute radiation effect was evaluated by measurement of the plasma level of Tgf-ß1 at (24 and 96hr) and by detection of skin contents of Tgf-ß1 (96hr). Long term response as fibrosis and leg contracture are under assessment.
Results: field dose and dose rate was quality assured and monitored for each irradiation. Variations of dose and dose rate are within 1%. Significant reduction of plasmatic Tgf-ß1 levels were observed for all FLASH irradiated group in comparison of Conv irradiation at 24hr (Flash60 p=0.028, Flash115 p=0.002 and SplitFlash60 p=0.004) and 96hr (Flash60 p<0.001, Flash115 p<0.001 and SplitFlash60 p<0.001). Reduction of Tgf-ß1 were also observed in skin 96hr after Flash irradiation in comparison to Conv irradiation.
Conclusion: results demonstrate a clinical proton therapy system delivering FLASH proton radiation reproducibly from 1 to 115Gy/s. The acute radiation response evaluation after rear hind limb irradiation with 35Gy indicate potential benefits of Flash proton beam scanning and long-term skin and muscle toxicity will be further evaluated.