Klinik und Poliklinik für Strahlentherapie, Universitätsklinikum Würzburg, Würzburg, Germany.
Radiat Oncol. 2013 Nov 8;8:263. doi: 10.1186/1748-717X-8-263.
The standard clinical protocol of image-guided IMRT for prostate carcinoma introduces isocenter relocation to restore the conformity of the multi-leaf collimator (MLC) segments to the target as seen in the cone-beam CT on the day of treatment. The large interfractional deformations of the clinical target volume (CTV) still require introduction of safety margins which leads to undesirably high rectum toxicity. Here we present further results from the 2-Step IMRT method which generates adaptable prostate IMRT plans using Beam Eye View (BEV) and 3D information.
Intermediate/high-risk prostate carcinoma cases are treated using Simultaneous Integrated Boost at the Universitätsklinkum Würzburg (UKW). Based on the planning CT a CTV is defined as the prostate and the base of seminal vesicles. The CTV is expanded by 10 mm resulting in the PTV; the posterior margin is limited to 7 mm. The Boost is obtained by expanding the CTV by 5 mm, overlap with rectum is not allowed. Prescription doses to PTV and Boost are 60.1 and 74 Gy respectively given in 33 fractions.We analyse the geometry of the structures of interest (SOIs): PTV, Boost, and rectum, and generate 2-Step IMRT plans to deliver three fluence steps: conformal to the target SOIs (S0), sparing the rectum (S1), and narrow segments compensating the underdosage in the target SOIs due to the rectum sparing (S2). The width of S2 segments is calculated for every MLC leaf pair based on the target and rectum geometry in the corresponding CT layer to have best target coverage. The resulting segments are then fed into the DMPO optimizer of the Pinnacle treatment planning system for weight optimization and fine-tuning of the form, prior to final dose calculation using the collapsed cone algorithm.We adapt 2-Step IMRT plans to changed geometry whilst simultaneously preserving the number of initially planned Monitor Units (MU). The adaptation adds three further steps to the previous isocenter relocation: 1) 2-Step generation for the geometry of the day using the relocated isocenter, MU transfer from the planning geometry; 2) Adaptation of the widths of S2 segments to the geometry of the day; 3) Imitation of DMPO fine-tuning for the geometry of the day.
We have performed automated 2-Step IMRT adaptation for ten prostate adaptation cases. The adapted plans show statistically significant improvement of the target coverage and of the rectum sparing compared to those plans in which only the isocenter is relocated. The 2-Step IMRT method may become a core of the automated adaptive radiation therapy system at our department.
为了在治疗当天的锥形束 CT 中恢复多叶准直器 (MLC) 段与靶区的一致性，前列腺癌的标准临床图像引导调强放疗方案引入了等中心重定位。临床靶区 (CTV) 的大分次间变形仍然需要引入安全边界，这导致直肠毒性不理想。在这里，我们展示了 2 步调强放疗方法的进一步结果，该方法使用 Beam Eye View (BEV) 和 3D 信息生成可适应的前列腺调强放疗计划。
在维尔茨堡大学医院 (UKW)，对中高危前列腺癌病例进行同步综合增强治疗。基于计划 CT，定义CTV 为前列腺和精囊底。CTV 扩展 10mm 得到 PTV；后界限制为 7mm。通过将 CTV 扩展 5mm 获得 Boost，不允许与直肠重叠。PTV 和 Boost 的处方剂量分别为 60.1Gy 和 74Gy，共 33 次。我们分析感兴趣结构 (SOIs) 的几何形状：PTV、Boost 和直肠，并生成 2 步调强放疗计划，以提供三个剂量分布：适形于靶区 SOIs (S0)、保护直肠 (S1)、以及狭窄的节段补偿由于直肠保护而导致的靶区 SOIs 欠剂量 (S2)。根据相应 CT 层中的靶区和直肠几何形状，为每个 MLC 叶片对计算 S2 节段的宽度，以获得最佳的靶区覆盖。然后，将生成的节段输入到 Pinnacle 治疗计划系统的 DMPO 优化器中进行权重优化和形状微调，然后使用崩溃圆锥算法进行最终剂量计算。
我们在保持最初计划的 Monitor Units (MU) 数量的同时，使 2 步调强放疗计划适应变化的几何形状。该适应在之前的等中心重定位的基础上增加了三个步骤：1）使用重新定位的等中心为当天的几何形状生成 2 步调强放疗计划，MU 从计划几何形状转移；2）适应 S2 节段的宽度以适应当天的几何形状；3）模拟当天几何形状的 DMPO 微调。
我们对 10 例前列腺适应病例进行了自动 2 步调强放疗适应。与仅进行等中心重定位的计划相比，适应后的计划显示出靶区覆盖率和直肠保护的统计学显著改善。2 步调强放疗方法可能成为我们部门自动化自适应放疗系统的核心。
