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Ultra-high dose rate effect on circulating immune cells: A potential mechanism for FLASH effect?
Jian-Yue Jin1, Anxin Gu2, Weili Wang3
1Department of Radiation Oncology, University Hospitals, Cleveland Medical Center, United States; Department of Radiation Oncology, Case Western Reserve University School of Medicine, Cleveland, United States.
Summary
Ultra-high dose rate FLASH radiotherapy significantly spares circulating immune cells compared to conventional doses. This reduced immune cell killing may partially explain the beneficial effects of FLASH therapy in preclinical studies.
Area of Science:
- Radiation Oncology
- Immunology
- Computational Biology
Background:
- FLASH radiotherapy (RT) offers tumor killing and normal tissue sparing, but its mechanisms are unclear.
- A hypothesis suggests reduced killing of circulating immune cells contributes to the FLASH effect.
Purpose of the Study:
- To model the impact of radiation dose rate on circulating immune cell survival.
- To investigate the contribution of immune cell sparing to FLASH RT efficacy.
Main Methods:
- A computational model simulated irradiated blood volumes and immune cell killing.
- The linear-quadratic model assessed cell death at ultra-high vs. conventional dose rates.
- Parameters included blood circulation, irradiation time, dose, and dose rate.
Main Results:
- FLASH RT dramatically reduced immune cell killing from 90-100% to 5-10%.
- A threshold dose rate of ~40 Gy/s was identified for mice, with a lower rate for humans.
- Sparing effects were dose-dependent, peaking at 30-50 Gy/fraction.
Conclusions:
- FLASH RT demonstrates significant sparing of circulating immune cells.
- This immune cell sparing is a potential mechanism underlying the observed FLASH effect in preclinical models.
