Medical Physics Support, Inc., Tampa, Florida 33634, United States of America.
Florida Urology Partners, Tampa, Florida 33606, United States of America.
Phys Med Biol. 2021 Jul 20;66(15). doi: 10.1088/1361-6560/abfc8e.
To evaluate how heterogeneity of the target dose and heterogeneity of intra-tumor radiosensitivity affect biologically effective dose (BED) and tumor control probability (TCP) depending on the number of fractions (Nf).The dependences of TCP and BED in the planning target volume onNfare studied using the linear-quadratic model. In the considered case, the nominal biologically effective dose(BEDnom)is fixed and the variances of the target dose (σD) and radiosensitivity (σα) are assumed to be small.By using series expansion of the survival probability of malignant cells, it is analytically shown that for smallσDandσαboth BED and TCP increase with increasingNfunder the conditionBEDnom=const.In addition, the dependences of BED and TCP onNffor different values ofσDandσαare studied by using an analytical expression for BED in the case of Gaussian distributions of both target dose and radiosensitivity.Small variations in the absorbed dose and intratumor radiosensitivity can significantly reduce BED and TCP. The decreases in these quantities can be reduced by increasing the number of fractions. The findings of this study indicate that hypofractionated regimens withNf=20and dose per fractiond≤5Gy can lead to higher BED and TCP compared to treatment regimens withNf≤5andd≥10Gy commonly used for stereotactic body radiation therapy (SBRT) and stereotactic radiosurgery (SRS).
为了评估目标剂量异质性和肿瘤内放射敏感性异质性如何根据分次剂量（Nf）的数量影响生物有效剂量（BED）和肿瘤控制概率（TCP）。使用线性二次模型研究了计划靶区中 TCP 和 BED 对 Nf 的依赖性。在考虑的情况下，固定名义生物有效剂量（BEDnom），并假设目标剂量（σD）和放射敏感性（σα）的方差较小。通过对恶性细胞存活概率的级数展开，分析表明，在 BEDnom=const 的条件下，对于较小的σD和σα，BED 和 TCP 随 Nf 的增加而增加。此外，通过使用目标剂量和放射敏感性均为高斯分布情况下的 BED 的解析表达式，研究了不同的σD和σα值下 BED 和 TCP 对 Nf 的依赖性。吸收剂量和肿瘤内放射敏感性的微小变化可显著降低 BED 和 TCP。通过增加分次剂量的数量可以减少这些数量的减少。本研究的结果表明，与立体定向体部放射治疗（SBRT）和立体定向放射外科（SRS）常用的 Nf≤5 和 d≥10Gy 的治疗方案相比，Nf=20 且每次剂量 d≤5Gy 的低分割方案可导致更高的 BED 和 TCP。
