Boekhoff M R, Defize I L, Borggreve A S, van Hillegersberg R, Kotte A N T J, Lagendijk J J W, van Lier A L H M W, Ruurda J P, Takahashi N, Mook S, Meijer G J
Department of Radiation Oncology, University Medical Center Utrecht, Utrecht University, the Netherlands.
Department of Radiation Oncology, University Medical Center Utrecht, Utrecht University, the Netherlands; Department of Surgery, University Medical Center Utrecht, Utrecht University, the Netherlands.
Radiother Oncol. 2021 Aug;161:16-22. doi: 10.1016/j.radonc.2021.05.005. Epub 2021 May 14.
This study aimed to assess the smallest clinical target volume (CTV) to planned target volume (PTV) margins for esophageal cancer radiotherapy using daily online registration to the bony anatomy that yield full dosimetric coverage over the course of treatment.
29 esophageal cancer patients underwent six T2-weighted MRI scans at weekly intervals. An online bone-match image-guided radiotherapy treatment of five fractions was simulated for each patient. Multiple conformal treatment plans with increasing margins around the CTV were created for each patient. Then, the dose was warped to obtain an accumulated dose per simulated fraction. Full target coverage by 95% of the prescribed dose was assessed as a function of margin expansion in six directions. If target coverage in a single direction was accomplished, then the respective margin remained fixed for the subsequent dose plans. Margins in uncovered directions were increased in a new dose plan until full target coverage was achieved.
The smallest set of CTV-to-PTV margins that yielded full dosimetric CTV coverage was 8 mm in posterior and right direction, 9 mm in anterior and cranial direction and 10 mm in left and caudal direction for 27 out of 29 patients. In two patients the curvature of the esophagus considerably changed between fractions, which required a 17 and 23 mm margin in right direction.
Accumulated dose analysis revealed that CTV-to-PTV treatment margins of 8, 9 and 10 mm in posterior & right, anterior & cranial and left & caudal direction, respectively, are sufficient to account for interfraction tumor variations over the course of treatment when applying a daily online bone match. However, two patients with extreme esophageal interfraction motion were insufficiently covered with these margins and were identified as patients requiring replanning to achieve full target coverage.
本研究旨在评估食管癌放疗中临床靶区（CTV）至计划靶区（PTV）的最小边界，采用每日在线配准至骨质解剖结构，以在治疗过程中实现剂量的完全覆盖。
29例食管癌患者每周进行一次6次T2加权MRI扫描。为每位患者模拟了一个5分次的在线骨匹配图像引导放疗治疗。为每位患者创建了多个围绕CTV增加边界的适形治疗计划。然后，将剂量进行变形以获得每个模拟分次的累积剂量。评估95%处方剂量对靶区的完全覆盖情况，作为六个方向上边界扩展的函数。如果在单个方向上实现了靶区覆盖，则在后续的剂量计划中相应的边界保持固定。在未覆盖方向上的边界在新的剂量计划中增加，直到实现靶区的完全覆盖。
29例患者中有27例，产生完全剂量学CTV覆盖的最小CTV至PTV边界为：后方和右侧8mm，前方和头侧9mm，左侧和尾侧10mm。在2例患者中，食管的曲率在分次之间有显著变化，这在右侧需要17mm和23mm的边界。
累积剂量分析表明，在应用每日在线骨匹配时，分别在后方和右侧、前方和头侧以及左侧和尾侧方向上8mm、9mm和10mm的CTV至PTV治疗边界足以考虑治疗过程中分次间肿瘤的变化。然而，2例食管分次间运动极端的患者，这些边界不足以实现完全覆盖，被确定为需要重新计划以实现靶区完全覆盖的患者。
