Klinik und Poliklinik für Strahlentherapie, Universität Würzburg, 97080 Würzburg, Germany.
Radiother Oncol. 2009 Nov;93(2):266-72. doi: 10.1016/j.radonc.2009.08.032. Epub 2009 Sep 30.
The ability of a geometry-based method to expeditiously adapt a "2-Step" step and shoot IMRT plan was explored. Both changes of the geometry of target and organ at risk have to be balanced. A retrospective prostate planning study was performed to investigate the relative benefits of beam segment adaptation to the changes in target and organ at risk coverage.
Four patients with six planning cases with extraordinarily large deformations of rectum and prostate were chosen for the study. A 9-field IMRT plan (A) using 2-Step IMRT segments was planned on an initial CT study. The plan had to fulfil all the requirements of a conventional high-quality step and shoot IMRT plan. To adapt to changes of the anatomy in a further CT data set, three approaches were considered: the original plan with optimized isocentre position (B), a newly optimized plan (C) and the original plan, adapted using the 2-Step IMRT optimization rules (D). DVH parameters were utilized for quantification of plan quality: D(99) for the CTV and the central planning target volume (PTV), D(95) for an outer PTV, V(95), V(80) and V(50) for rectum and bladder.
The adapted plan (D) achieved almost the same target coverage as the newly optimized plan (C). Target coverage for plan B was poor and for the organs at risk, the rectum V(80) was slightly increased. The volume with more than 95% of the target dose (V(95)) was 1.5+/-1.5 cm(3) for the newly optimized plan (C), compared to 2.2+/-1.3 cm(3) for the original plan (A) and 7.2+/-4.8 cm(3) (B) on the first and the second CT, respectively. The adapted plan resulted in 4.3+/-2.1 cm(3) (D), an intermediate dose load to the rectum. All other parameters were comparable for the newly optimized and the adapted plan.
The first results for adaptation of interfractional changes using the 2-Step IMRT algorithm are encouraging. The plans were superior to plans with optimized isocentre position and only marginally inferior to a newly optimized plan.
本研究旨在探索一种基于几何形状的方法，以快速调整“两步”步进式调强放疗计划。目标和危及器官的几何形状变化都需要平衡。进行了一项回顾性前列腺计划研究，以调查在靶区和危及器官覆盖变化的情况下，光束段适应的相对益处。
选择了 4 名患者的 6 个计划病例，这些患者的直肠和前列腺存在非常大的变形。使用 2 步调强分割法（2-Step）在初始 CT 研究上计划了 9 野调强放疗计划（A）。该计划必须满足高质量的常规步进式调强放疗计划的所有要求。为了适应进一步 CT 数据集的解剖结构变化，考虑了三种方法：具有优化等中心位置的原始计划（B），新优化计划（C）和使用 2-Step 调强优化规则（D）进行的原始计划。剂量体积直方图（DVH）参数用于量化计划质量：CTV 和中央计划靶区（PTV）的 D（99），外 PTV 的 D（95），直肠和膀胱的 V（95），V（80）和 V（50）。
调整后的计划（D）几乎与新优化计划（C）具有相同的靶区覆盖率。计划 B 的靶区覆盖率较差，而对于危及器官，直肠 V（80）略有增加。新优化计划（C）的目标剂量超过 95％的体积（V（95））为 1.5+/-1.5cm3，而原始计划（A）和第一次 CT 的原始计划（B）分别为 2.2+/-1.3cm3 和 7.2+/-4.8cm3。调整后的计划（D）导致直肠的剂量负荷为 4.3+/-2.1cm3，处于中等水平。新优化计划和调整后的计划的所有其他参数均相当。
使用 2 步调强放疗算法进行分次间变化的自适应的初步结果令人鼓舞。这些计划优于优化等中心位置的计划，仅略逊于新优化计划。
