2841 - Verifying the Protective Effect of Miniaturized High-Energy X-Rays FLASH-RT Device and the Impact of Irradiation Fraction on Normal Tissues

B. Lin¹, H. Du¹, X. Hao¹, Y. Liao¹, B. Lin¹, R. Gu¹, Y. Zhu², T. Wang¹, D. Wang³, X. Mao¹, J. Li¹, F. Gao¹, Y. Yang⁴, J. Wang⁴, D. Wu⁴, and X. Du¹; ¹Departmant of Oncology, Mianyang Central Hospital, School of Medicine, University of Electronic Science and Technology of China, Mianyang, China, ²Laboratory Department, Mianyang Central Hospital, School of Medicine, University of Electronic Science and Technology of China, Mianyang, China, ³Departmant of Urology, Mianyang Central Hospital, School of Medicine, University of Electronic Science and Technology of China, Mianyang, China, ⁴Institute of Applied Electronics, China Academy of Engineering Physics, Mianyang, China

Purpose/Objective(s): This study aimed to verify whether the newly miniaturized high-energy X-rays FLASH radiotherapy device (mHEXs) could produce ultrahigh dose rate (FLASH) X-rays and trigger the protective effect on normal tissues. Additionally, it sought to investigate the impact of varying fractions on normal tissues when exposed to the same total dose. Materials/

Methods: EBT3 radiochromic film and fast current transformer were used to measure absolute dose and pulsed beam of mHEXs. C57BL/6 female mice were irradiated with sham (control), FLASH-RT, and conventional dose rate radiotherapy (CONV-RT) to verify the protective effect of mHEXs in lung, intestine and skin. The irradiation schemes for the three organs were as follows:(1)lung: control (0Gy), FLASH-1(30Gy × 1fraction), FLASH-3(10Gy × 3fraction, 30s intervals) and CONV(30Gy × 1fraction); (2)intestine: control (0Gy), FLASH-1(12Gy × 1fraction), FLASH-3(4Gy × 3fractions, 30s interval) and CONV(12Gy × 1fraction); (3)skin:control (0Gy), FLASH-1(36Gy × 1fraction), FLASH-3(12Gy × 3fractions, 30s interval) and CONV (36Gy × 1fraction). The survival status and normal tissue damage of each group were observed.
Results: The average dose rate of FLASH-RT and CONV-RT were 240-340Gy/s and 0.07Gy/s, respectively. For the lung, the 6 weeks survival rates of control, FLASH-1, FLASH-3 and CONV were 100%, 84.62%, 60% and 7.69%, respectively (P < 0.05). Hematoxylin-eosin (H&E) staining of the lung sections revealed similar alveolar structures between the FLASH-1, FLASH-3 and control groups, whereas more disintegrated alveolar structures were observed in the CONV group. For the intestine, the 6 weeks survival rates of control, FLASH-1, FLASH-3 and CONV were 100%, 100%, 20% and 40%, respectively (P < 0.05). H&E staining of the intestine sections showed that FLASH-1 induced less acute intestinal damage compared to FLASH-3 and CONV. For the skin, the incidence of = grade 2 radiation dermatitis after 2 weeks post-irradiation in the control, FLASH-1, FLASH-3 and CONV were 0%, 0%, 14.29% and 85.71%, respectively (P < 0.05). H&E staining of skin sections revealed similar epithelial thicknesses between the FLASH-1, FLASH-3 and control groups, whereas more hyperplasias were observed in the CONV group.
Conclusion: The mHEXs can produce ultrahigh dose rate X-rays, and the average dose rate exceeds 40Gy/s. mHEXs can trigger a protective effect on lung, intestine and skin tissues, and increasing the number of fractions of FLASH irradiation may weak its protective effect on normal tissues.