Kuperman V Y, Lubich L M
Florida Hospital, Tampa, FL, 33613, USA.
Florida Urology Partners, Tampa, FL, 33606, USA.
Med Phys. 2020 Oct;47(10):5383-5391. doi: 10.1002/mp.14343. Epub 2020 Sep 3.
To assess the role of reoxygenation of hypoxic tumor cells in hypofractionated radiotherapy of prostate cancer.
The considered radiobiological model is based on the assumption of two populations (compartments) of cells: oxygenated (aerobic) cells and hypoxic cells. After each fraction of radiation, some of the hypoxic cells reoxygenate while a fraction of initially aerobic cells becomes hypoxic. The kinetics of this process between successive treatments is described by coupled, first-order differential equations. To determine the effect of reoxygenation on cell kill in the treatment target, we utilize the linear-quadratic (LQ) model assuming different radiosensitivities for the aerobic and hypoxic cells.
Analytical solutions for the number of surviving malignant cells are obtained for special cases of slow and fast reoxygenation. The radiobiological effect of reoxygenation for different fractionation regimens is also evaluated numerically.
In this study, a radiobiological model for kinetics of reoxygenation in tumors is used to evaluate different fractionation schedules in radiotherapy of prostate cancer. The obtained results indicate that in the case of low alpha/beta ratio for malignant cells (e.g., = 1.5 Gy), treatment schedule with 4-10 fractions and dose per fraction >4-5 Gy can result in increased cell kill in the treatment target at the same level of rectal toxicity as compared to conventional fractionation. The findings of this study also suggest that radiotherapy of the prostate with 1-3 fractions can be radiobiologically inferior to treatments with greater number of fractions.
评估缺氧肿瘤细胞再氧合在前列腺癌大分割放疗中的作用。
所考虑的放射生物学模型基于细胞的两个群体（区室）的假设：富氧（需氧）细胞和缺氧细胞。每次放疗后，一些缺氧细胞会再氧合，而一部分初始的需氧细胞会变成缺氧细胞。连续治疗之间这个过程的动力学由耦合的一阶微分方程描述。为了确定再氧合对治疗靶区细胞杀伤的影响，我们利用线性二次（LQ）模型，假设需氧细胞和缺氧细胞具有不同的放射敏感性。
针对慢再氧合和快再氧合的特殊情况，获得了存活恶性细胞数量的解析解。还对不同分割方案的再氧合放射生物学效应进行了数值评估。
在本研究中，使用肿瘤再氧合动力学的放射生物学模型来评估前列腺癌放疗中的不同分割方案。获得的结果表明，对于恶性细胞α/β比值较低的情况（例如，α/β = 1.5 Gy），与传统分割相比，4 - 10次分割且每次分割剂量>4 - 5 Gy的治疗方案在直肠毒性相同水平下可导致治疗靶区细胞杀伤增加。本研究结果还表明，1 - 3次分割的前列腺放疗在放射生物学上可能不如分割次数更多的治疗。
