Cao Yangsen, Zhu Xiaofei, Zhang Yu, Yu Chunshan, Liu Yongming, Sun Yongjian, Dai Zhitao, Guo Xueling, Ju Xiaoping, Zhang Huojun
Department of Radiation Oncology, Changhai Hospital Affiliated to Second Military Medical University, Shanghai, China.
Department of Radiology, Changhai Hospital Affiliated to Second Military Medical University, Shanghai, China.
Med Dosim. 2018;43(3):207-213. doi: 10.1016/j.meddos.2017.08.008. Epub 2017 Oct 6.
To provide a modified formula consistent with the Monte Carlo (MC) algorithm for dose calculations during stereotactic ablative body radiotherapy for non-small cell lung cancer. Seventy CyberKnife treatment plans were calculated and analyzed by MC and ray-tracing (RT) algorithms, separately. Parameters of treatment plans were compared, and those associated with differences of dose distributions were analyzed to establish a modified formula. Gross tumor volume and tumor tracking volume (TTV) were defined as the evident disease on the sequences of the window width and level of the lung and the mediastinum. Additionally, the formula was validated by another 20 plans. The prescription dose of the 90 patients was 60 Gy/5f. The RT algorithm overestimated the planning target volume (PTV) D by an average of 8.59 Gy and the gross tumor volume D by an average of 5.84 Gy. The homogeneity index of PTV was underestimated by 0.11 on average, whereas the conformity index and new conformity index was underestimated by 0.05. The RT algorithm overestimated the dose distribution to the spinal cord by 2.23 Gy, the esophagus by 1.96 Gy, the trachea by 1.89 Gy, the left-sided bronchus by 1.77 Gy, the right-sided bronchus by 1.64 Gy, and the heart by 2.16 Gy. The average whole-lung dose volumes of lung tissues and dose volumes of V were overestimated by 2.69 Gy and 7.52%, respectively. A power function distribution (R = 0.8626) was confirmed between PTV D and TTV volumes. PTV D calculated by the MC algorithm could be computed easily with TTV and PTV D calculated by the RT algorithm based on the formula. The modified equation was more consistent with MC algorithm than with other formula, which could be a reference to those not accessible to the MC algorithm.
为提供一种与蒙特卡罗（MC）算法一致的修正公式，用于非小细胞肺癌立体定向消融体部放疗期间的剂量计算。分别采用MC算法和射线追踪（RT）算法计算并分析了70个射波刀治疗计划。比较了治疗计划的参数，并分析了与剂量分布差异相关的参数，以建立修正公式。将大体肿瘤体积和肿瘤追踪体积（TTV）定义为肺部和纵隔窗宽及窗位序列上的明显病变。此外，通过另外20个计划对该公式进行了验证。90例患者的处方剂量为60 Gy/5次分割。RT算法平均高估计划靶体积（PTV）剂量8.59 Gy，大体肿瘤体积剂量平均高估5.84 Gy。PTV的均匀性指数平均低估0.11，而适形指数和新适形指数平均低估0.05。RT算法高估了脊髓的剂量分布2.23 Gy，食管1.96 Gy，气管1.89 Gy，左侧支气管1.77 Gy，右侧支气管1.64 Gy，心脏2.16 Gy。肺组织的平均全肺剂量体积和V的剂量体积分别高估2.69 Gy和7.52%。PTV剂量与TTV体积之间证实了幂函数分布（R = 0.8626）。基于该公式，利用RT算法计算的TTV和PTV剂量可以轻松计算出MC算法计算的PTV剂量。修正后的方程与MC算法的一致性优于其他公式，可为无法使用MC算法的情况提供参考。
