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Conference Proceeding

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Medical Physics


Purpose: Radiation therapy is a double-edged sword with regard to its immunomodulatory effect. It is critical to find how it is affected by dose rate. Thus, we developed an analytic model for calculating the number of immune cells receiving radiation. Methods: Suppose the blood is received radiation by constant dose rate. The blood is one-way flow without circulation in the radiation delivery at a constant velocity. Two kinds of lung treatment regimens were considered standard delivery 2Gy per fx total 30fx and hypo-fractionation SBRT 12 Gy per fx total 5 fx. Two different dose rates were simulated for standard treatment: conventional dose rate (0.1,0.2 and 1 Gy/s) and low dose rate (0.01, 0.02 and 0.05Gy/s). Two different dose rate were simulated for SBRT including FLASH (40, 60 and 80Gy/s) and conventional dose rate (0.1, 0.2 and 1 Gy/s) are considered. Single fraction Dose-number histogram (SF-DNH)s are plotted as cumulative histogram relating radiation dose to number of immune cells receiving dose for standard delivery and SBRT, FLASH , and low dose rate. The killing effect to immune cells is evaluated for threshold 0.5 Gy. Results: The SF-DNH curves are line segments with same intercept for standard delivery, FLASH and low dose rate accordingly. Their slopes are negative that are proportional to blood velocity and dose at mean while inversely proportional to dose rate. FLASH segments are quite flat with intercept at prescribed dose. Therefore, either higher dose rate or enough low dose rate can reduce killing to immune cells. FLASH may be even more effective in these regards. Conclusion: This is the first analytic model to explain the dose rate effect on the immune in radiotherapy. This work paved the roadmap for implementing such new model in a routine clinic and provided a methodology to explore the immune dose computation





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American Association of Physicists in Medicine 65th Annual Meeting & Exhibition, July 23-27, 2023, Houston, TX