Abstract Body

We introduced three studies conducted on high-energy X-ray FLASH in China.

The first study was to explore the optimal dose rate and dose fraction of ultra-high dose rate X-ray radiation (FLASH-RT) in thoracic radiotherapy. The study suggests that FLASH irradiation at 250Gy/s can reduce the incidence of acute radiation pneumonitis in mice compared with 100Gy/s. When mice were irradiated with 250Gy/s FLASH X-rays, the survival rate of mice delivered with a dose of 30Gy was better than that of mice irradiated twice. However, under the same experimental conditions, no significant difference was observed in the toxicity of late radiation response in mice.

The second study investigated the anti-tumor effect, immune response, and intestinal injury in breast cancer-bearing mice after FLASH-RT and conventional dose rate radiotherapy (CONV-RT). FLASH-RT and CONV-RT effectively suppressed tumor growth and promoted CD8+ T cell influx into the tumor. FLASH-RT resulted in a smaller weight and a higher proliferative rate of CD8+ T cells in the spleen than CONV-RT, which might indicate a different systematic immune effect between FLASH-RT and CONV-RT. FLASH-RT significantly spared the intestine from early damage.

The third study used FLASH-RT to counteract intestinal toxicity in radioimmunotherapy. Meanwhile, FLASH X-ray was as competent as CONV-RT in boosting the anti-tumor immune response initiated by cGAS activation and achieved equal tumor control in metastasis burdens when combined with anti-PD-L1 administration. Together, the present study revealed an encouraging protective effect of FLASH X-ray upon the normal tissue without compromising the systemic anti-tumor response when combined with immunological checkpoint inhibitors, providing the rationale for testing this combination as a clinical application in radioimmunotherapy.