2307 - The Durably Antitumor Effect by FLASH Radiotherapy (FLASH-RT) Combined with Spatially Fractionated Radiotherapy (SFRT)
Presenter(s)
J. Zhou1, S. Lu1, D. Li2, and L. Lintao3; 1Department of Radiation Oncology, Radiation Oncology Key Laboratory of Sichuan Province, Sichuan Cancer Hospital & Institute, Sichuan Cancer Center, Affiliated Cancer Hospital of University of Electronic Science and Technology of China, Chengdu, China, 2Department of Radiation Oncology, Sichuan ClinicalResearchCenter for Cancer,Sichuan Cancer Hospital &Institute,SichuanCancerCenter ,School of Medicine,University of Electronic Science and Technology of China, Chengdu, China, 3Sichuan Cancer Hospital and Research Institute, University of Electronic Science and Technology of China, Radiation Oncology Department, Chengdu, China
Purpose/Objective(s): Both FLASH radiotherapy (FLASH-RT) and spatially fractionated radiation therapy (SFRT) demonstrate remarkable normal tissue sparing while preserving antitumor efficacy comparable to conventional radiotherapy (CONV-RT). However, FLASH-RT and SFRT are quite different therapeutical strategies, FLASH-RT adopts ultra-high dose rates to protect normal tissue temporally, while SFRT uses alternating radiation of peak and valley dose to protect normal tissue spatially. We wondered whether FLASH-RT combined with SFRT exert a winning alliance.
Materials/Methods: The combination of FLASH-RT and SFRT (minibeam) was performed on a lead shielding plate (1mm aperture, 2mm center-to-center distance), which allowed electron ultra-high dose rate radiation to go through and form a peak and valley dose distribution. The in vivo experiment was performed on Balb/c mice with 4T1 breast cancer cell line. After the tumor reached 200-300 mm3, the mice were divided into four groups, including control group (tumor-bearing only), CONV-RT (0.5 Gy/s, 15 Gy), CONV-RT+SFRT (0.5 Gy/s, 5 Gy average dose), FLASH-RT+SFRT (200 Gy/s, 5 Gy average dose). Upon irradiation, the tumor volume, mouse weight, and dissected tumor weight were determined for within 2 weeks.
Results: Ultra-high dose rate radiation passed through the lead shielding plate and formed an area of 15 Gy peak dose and 2 Gy valley dose (peak-to-valley dose ratio is nearly 7.5). On the 7th day after irradiation, the tumor volume in CONV-RT, FLASH +SFRT, and FLASH-RT+SFRT group were lower than that in control group (p< 0.05). Ten days post irradiation, we observed lower tumor volume in the FLASH-RT+SFRT group than that in CONV-RT group (p< 0.05), and this difference appears more remarkably upon 13 days after irradiation (p< 0.01). Additionally, we observed comparable mice weight among the groups, regardless of radiation modalities, exhibiting a high safety by FLASH-RT and SFRT.
Conclusion: Compared to conventional radiotherapy, combining FLASH and spatially fractionated radiation therapy had a durably antitumor effect and superior safety, which may represent a promising radiotherapy modality.