LTSI, Université de Rennes 1, Campus de Beaulieu, Rennes, F-35042, France.
INSERM, U1099, Campus de Beaulieu, Rennes, F-35042, France.
Med Phys. 2018 Apr;45(4):1379-1390. doi: 10.1002/mp.12818. Epub 2018 Mar 15.
In the context of adaptive radiation therapy (ART) for locally advanced cervical carcinoma (LACC), this study proposed an original cone-beam computed tomography (CBCT)-guided "Evolutive library" and evaluated it against four other known radiotherapy (RT) strategies.
For 20 patients who underwent intensity-modulated radiation therapy (IMRT) for LACC, three planning CTs [with empty (EB), intermediate (IB), and full (FB) bladder volumes], a CT scan at 20 Gy and bi-weekly CBCTs for 5 weeks were performed. Five RT strategies were simulated for each patient: "Standard RT" was based on one IB planning CT; "internal target volume (ITV)-based RT" was an ITV built from the three planning CTs; "RT with one mid-treatment replanning (MidTtReplan)" corresponded to the standard RT with a replanning at 20 Gy; "Pretreatment library ART" using a planning library based on the three planning CTs; and the "Evolutive library ART", which was the "Pretreatment library ART" strategy enriched by including some CBCT anatomies into the library when the daily clinical target volume (CTV) shape differed from the ones in the library. Two planning target volume (PTV) margins of 7 and 10 mm were evaluated. All the strategies were geometrically compared in terms of the percentage of coverage by the PTV, for the CTV and the organs at risk (OAR) delineated on the CBCT. Inadequate coverage of the CTV and OARs by the PTV was also assessed using deformable image registration. The cumulated dose distributions of each strategy were likewise estimated and compared for one patient.
The "Evolutive library ART" strategy involved a number of added CBCTs: 0 for 55%; 1 for 30%; 2 for 5%; and 3 for 10% of patients. Compared with the other four, this strategy provided the highest CTV geometric coverage by the PTV, with a mean (min-max) coverage of 98.5% (96.4-100) for 10 mm margins and 96.2% (93.0-99.7) for 7 mm margins (P < 0.05). Moreover, this strategy significantly decreased the geometric coverage of the bowel. CTV undercoverage by PTV occurred in the anterior and superior uterine regions for all strategies. The dosimetric analysis at 7 mm similarly demonstrated that the "Evolutive library ART" increased the V of the CTV by 27%, 20%, 13%, and 28% compared with "Standard RT", "ITV-based RT", "MidTtReplan", and "Pretreatment library ART", respectively. The dose to the bowel was also decreased by the "Evolutive library ART" compared with that by the other strategies.
The "Evolutive library ART" is a personalized ART strategy that comprises a pretreatment planning library of three CT scans, enriched for half of the patients by one to three per-treatment CBCTs. This original strategy increased both the CTV coverage and bowel sparing compared with all the other tested strategies and enables us to consider a PTV margin reduction.
在局部晚期宫颈癌（LACC）的自适应放疗（ART）背景下，本研究提出了一种原始的锥形束 CT（CBCT）引导的“进化文库”，并将其与其他四种已知的放疗（RT）策略进行了比较。
对 20 名接受 LACC 调强放疗（IMRT）的患者进行了研究，这些患者分别进行了三次调强放疗（IMRT）计划 CT 扫描（空（EB）、中间（IB）和全（FB）膀胱容积）、一次 20 Gy 的 CT 扫描和五次每周的 CBCT 扫描，共五周。对每位患者模拟了五种 RT 策略：“标准 RT”基于一个 IB 计划 CT；“基于内部靶区（ITV）的 RT”是从三个计划 CT 构建的 ITV；“具有中期治疗再计划（MidTtReplan）的 RT”对应于标准 RT 与 20 Gy 时的再计划；“基于预处理库的 ART”使用基于三个计划 CT 的计划库；“进化文库 ART”是在每日临床靶区（CTV）形状与库中的形状不同时，将一些 CBCT 解剖结构纳入库中的“基于预处理库的 ART”策略。评估了 7 和 10 mm 两种计划靶区（PTV）边界。从 PTV 对 CTV 和勾画的危及器官（OAR）的覆盖百分比方面，对所有策略进行了几何比较。使用变形图像配准评估了 CTV 和 OAR 对 PTV 的覆盖不足。同样估计并比较了每个策略的累积剂量分布。
“进化文库 ART”策略涉及一些附加的 CBCT：55%的患者为 0 次；30%的患者为 1 次；5%的患者为 2 次；10%的患者为 3 次。与其他四种策略相比，该策略提供了最高的 PTV 对 CTV 的几何覆盖，10mm 边界的平均（最小-最大）覆盖率为 98.5%（96.4-100），7mm 边界的覆盖率为 96.2%（93.0-99.7）（P<0.05）。此外，该策略显著降低了肠道的几何覆盖。所有策略中，CTV 在前部和上部子宫区域都有 PTV 覆盖不足。7mm 的剂量分析同样表明，与“标准 RT”、“基于 ITV 的 RT”、“MidTtReplan”和“预处理库 ART”相比，“进化文库 ART”分别增加了 27%、20%、13%和 28%的 CTV V。与其他策略相比，肠道的剂量也降低了。
“进化文库 ART”是一种个性化的 ART 策略，包括三个 CT 扫描的预处理计划库，对于一半的患者，通过一到三次每次治疗的 CBCT 进行补充。与所有其他测试策略相比，这种原始策略增加了 CTV 的覆盖范围和肠道保护，使我们能够考虑减少 PTV 边界。
