Department of Radiology, Ofuna Chuo Hospital, Kanagawa, Japan.
Department of Radiation Oncology, Tokai University, Kanawaga, Japan.
Pract Radiat Oncol. 2012 Jan-Mar;2(1):46-53. doi: 10.1016/j.prro.2011.06.001. Epub 2011 Jul 23.
To assess the most suitable value of a relative prescribed dose in clinical treatment plans of stereotactic body radiotherapy (SBRT) using dynamic conformal multiple arc therapy to treat lung tumors.
We retrospectively generated alternative SBRT plans for typical examples of 8 patients who had been treated with SBRT for a lung tumor with a prescribed dose of 50 Gy in 5 fractions. The prescribed dose had been defined as 80% of the maximal dose in the planning target volume (PTV) ("the 80% isodose plan"). Alternative 20%-90% isodose plans at 10% intervals were generated (64 plans; 8 plans for each of the 8 patients), and factors related to leaf margins, target volume, normal lung volume, and monitor units were compared using dose-volume histogram analysis.
We could generate all the 64 plans. Compared with the 80% isodose plan, the V20 and mean lung dose (MLD) were both lower in the 60% plan; the V20 was approximately 19% lower (4.72% vs 3.84%) and the MLD was 13% lower (4.0 Gy vs 3.5 Gy). Mean PTV and ITV doses were higher in the lower percentage isodose plans. Compared with the 80% isodose plan, in the 60% isodose plan the mean PTV was 19% higher (56.1 Gy vs 66.8 Gy) and the mean ITV was 30% higher (59.6 Gy vs 77.4 Gy). The mean total monitor units increased more steeply than did the mean homogeneity index. The mean conformity index values in the 60% and 70% isodose plans were less than 1.15.
The 60% isodose plan was considered the best plan in this analysis because of the lower comparative dosimetric factors in normal lung tissue (including V20 and MLD) and the higher comparative mean PTV and internal target volume doses achieved, along with good conformity index values. In clinical use, accurate estimation and commissioning should be performed for the dose distribution prior to selecting a plan. Further investigation is warranted to determine whether the calculated dosimetric advantages result in improved outcomes.
使用动态适形多弧治疗来评估立体定向体部放疗（SBRT）治疗肺部肿瘤的临床治疗计划中相对规定剂量的最佳值。
我们回顾性地为 8 例接受 SBRT 治疗的肺部肿瘤患者生成了替代 SBRT 计划，这些患者的处方剂量为 50 Gy 分 5 次。规定剂量被定义为计划靶区（PTV）中最大剂量的 80%（“80%等剂量线计划”）。以 10%的间隔生成了替代的 20%-90%等剂量线计划（64 个计划；每个患者 8 个计划），并使用剂量-体积直方图分析比较了与叶间隙、靶区、正常肺体积和监测单位相关的因素。
我们能够生成所有 64 个计划。与 80%等剂量线计划相比，60%等剂量线计划的 V20 和平均肺剂量（MLD）均较低；V20 降低了约 19%（4.72%对 3.84%），MLD 降低了 13%（4.0 Gy 对 3.5 Gy）。较低百分比等剂量线计划中的平均 PTV 和 ITV 剂量较高。与 80%等剂量线计划相比，在 60%等剂量线计划中，平均 PTV 升高了 19%（56.1 Gy 对 66.8 Gy），平均 ITV 升高了 30%（59.6 Gy 对 77.4 Gy）。平均总监测单位的增加比平均均匀性指数更为陡峭。60%和 70%等剂量线计划中的平均适形指数值小于 1.15。
在这项分析中，60%等剂量线计划被认为是最佳计划，因为它在正常肺组织中具有较低的比较剂量学因素（包括 V20 和 MLD），同时也具有较高的平均 PTV 和内部靶区剂量，以及良好的适形指数值。在临床应用中，在选择计划之前，应准确估计和调试剂量分布。需要进一步研究以确定计算出的剂量学优势是否会带来更好的结果。
