FLASH reduces radiation-induced oral mucositis in a mouse model of Fanconi anemia

Patients with Fanconi anemia (FA) are particularly susceptible to developing squamous cell carcinomas of the head and neck regions due to impaired DNA repair pathways. However, their hypersensitivity to DNA damaging agents can limit effective treatment with standard radiotherapy due to severe side effects and complications. In pre-clinical models, ultra-rapid FLASH radiotherapy (FLASH) has been demonstrated to reduce radiation-induced toxicity to multiple normal tissues while maintaining similar tumor control compared to conventional dose rate radiotherapy (CONV) in a wild-type background. Here, we investigated the safety of FLASH for treatment of the head and neck region in a mouse model of FA. The oral cavity of 129/Sv wild-type (WT) and Fanca-knockout (KO) mice was irradiated with a single dose of electron beam FLASH or CONV to evaluate radiation-induced toxicity in non-tumor bearing mice. Fanca WT and KO mice were irradiated with 25 and 18 Gy, respectively, of FLASH (190 Gy/sec) or CONV (0.2 Gy/sec), and tongues were harvested at 12 hours (hpi) and 10 days (dpi) post-irradiation. Following excision, tongues were stained with toluidine blue to visualize ulceration. At 10 dpi, FLASH-irradiated tongues in both genetic backgrounds demonstrated a reduced area of ulceration, expressed as a fraction of total tongue area, at the dorsal surface compared to CONV-irradiated counterparts. Histopathological analysis of the tongue revealed lower mucositis severity scores, reflected by decreased epithelial thinning and ulceration, in FLASH-irradiated tongues compared to CONV-irradiated ones. Analysis of gamma-H2AX foci formation at 12 hpi demonstrated a decreased number of foci in the WT background with FLASH compared to CONV and a similar trend in the KO background. These findings suggest a potential normal tissue sparing effect with FLASH and hold important clinical implications for the treatment of patients with Fanconi anemia and head and neck cancers.