Medical Physics Support, Inc., Tampa, FL 33634, United States of America.
Florida Urology Partners, Tampa, FL 33606, United States of America.
Phys Med Biol. 2021 Feb 12;66(1):01NT02. doi: 10.1088/1361-6560/abd0d1.
To evaluate the effect of dose heterogeneity in the treatment target on biologically effective dose (BED) for frequently used hypofractionation regimens in stereotactic body radiation therapy (SBRT).
In the case of non-uniform target dose, BED in the planning target volume (PTV) is determined by using the linear-quadratic model. An expression for BED is obtained for an arbitrary dose distribution in the PTV in the case of small variance of the target dose. Another analytical expression for BED is obtained by assuming a Gaussian dose distribution in the target.
Analytical expressions for BED as a function of the variance of the target dose have been derived. It is shown that a relatively small dose inhomogeneity (<5%-6%) can cause a significant reduction (i.e. >10%) in the corresponding BED and equivalent uniform dose (EUD) compared to the case of uniform target dose.
Small variations in the absorbed dose can significantly reduce BED and EUD in the PTV. The effect of dose non-uniformity on BED increases with increasing dose per fraction. The observed reduction in BED compared to that for uniform target dose can be several times greater for SBRT than for standard fractionation with dose per fraction varying between 1.8 and 2 Gy.
评估立体定向体部放射治疗（SBRT）中常用的亚分次治疗方案中靶区剂量不均匀对生物有效剂量（BED）的影响。
在靶区剂量不均匀的情况下，通过线性二次模型来确定计划靶区（PTV）中的 BED。在靶区剂量方差较小的情况下，得到了 PTV 中任意剂量分布的 BED 表达式。通过假设靶区中存在高斯剂量分布，得到了另一个 BED 的解析表达式。
推导出了靶区剂量方差的 BED 解析表达式。结果表明，与均匀靶区剂量相比，相对较小的剂量不均匀性（<5%-6%）会导致相应的 BED 和等效均匀剂量（EUD）显著降低（即>10%）。
吸收剂量的微小变化会显著降低 PTV 中的 BED 和 EUD。剂量非均匀性对 BED 的影响随每分次剂量的增加而增加。与均匀靶区剂量相比，SBRT 的 BED 降低幅度可能比标准分次治疗（每分次剂量在 1.8 至 2 Gy 之间）大几倍。
