ESTRO 2024 - Abstract Book

S5272 ESTRO 2024 doses between 20-50 Gy for CONV, and 30-65 Gy for FLASH. The leg was placed in the middle of a Spread-out Bragg Peak (SOBP) generated from a single-energy beam using a 3D-printed static range modulator. Acute skin toxicity quantified by hair loss, moist desquamation and toe separation was monitored daily within 29 days post treatment. Late toxicity in the form of fibrotic development measured by leg extendibility was monitored biweekly until 30 weeks post-treatment. Radiobiology - Normal tissue radiobiology

Results:

Dose-response curves for early damage were produced from the percentage of mice reaching severe acute skin toxicity. For the same mice, the percentage of mice with radiation-induced fibrosis in the leg was used to produce late damage dose-response curves. The chosen doses comprise full dose-response curves for both CONV and FLASH radiation (Fig. 1&2). Comparison of severe acute skin toxicity following radiation shows a shift of the dose response curve for FLASH to higher doses (Fig. 1). This reflects a tissue-sparing effect of FLASH compared to conventional single-fraction radiation. The obtained protection ratio of FLASH for acute skin toxicity was 1.26. Fibrotic development similarly shows a dose-response curve shift for FLASH, signifying a sparing effect for FLASH relative to CONV (Fig. 2). The obtained protection ratio of FLASH for fibrosis was 1.24.

Conclusion: