South Western Clinical School, Faculty of Medicine, University of New South Wales, Sydney, New South Wales, Australia.
Liverpool and Macarthur Cancer Therapy Centres, Sydney, New South Wales, Australia.
J Med Radiat Sci. 2021 Sep;68(3):298-309. doi: 10.1002/jmrs.469. Epub 2021 May 2.
Stereotactic ablative body radiotherapy (SABR) is currently indicated for inoperable, early-stage non-small cell lung carcinoma (NSCLC). Advancements in image-guidance technology continue to improve treatment precision and enable reductions in planning safety margins. We investigated the dosimetric benefits of margin reduction, its potential to extend SABR to more NSCLC patients and the factors influencing plan acceptability.
This retrospective analysis included 61 patients (stage IA-IIIA) treated with conventional radiotherapy. Patients were ineligible for SABR due to tumour size or proximity to organs at risk (OAR). Using Pinnacle auto-planning, three SABR plans were generated for each patient: a regular planning target volume margin plan, a reduced margin plan (gross tumour volume GTV+3 mm) and a non-margin plan. Targets were planned to 48Gy/4 or 50Gy/5 fractions depending on location. Plans were compared in terms of target coverage, OAR doses and dosimetric acceptability based on local guidelines. Predictors of acceptability were investigated using logistic regression analysis.
Compared to regular margin plans, both reduced margin and non-margin plans resulted in significant reductions to almost all dose constraints. Dose conformity was significantly worse in non-margin plans (P < 0.05) and strongly correlated with targets' surface area/volume ratio (R = 0.9, P < 0.05). 26% of reduced margin plans were acceptable, compared to 54% of non-margin plans. GTV overlap with OARs significantly affected plan acceptability (OR 0.008, 95% CI 0.001-0.073).
Margin reduction significantly reduced OAR doses enabling acceptable plans to be achieved for patients previously excluded from SABR. Indications for lung SABR may broaden as treatment accuracy continues to improve; further work is needed to identify patients most likely to benefit.
立体定向消融体放射治疗（SABR）目前适用于无法手术的早期非小细胞肺癌（NSCLC）。影像引导技术的进步不断提高治疗精度，并能够减少计划安全裕度。我们研究了减少裕度的剂量学优势，其将 SABR 扩展到更多 NSCLC 患者的潜力以及影响计划可接受性的因素。
本回顾性分析纳入了 61 例（IA-IIIA 期）接受常规放疗的患者。由于肿瘤大小或靠近危及器官（OAR），患者不符合 SABR 条件。使用 Pinnacle 自动计划，为每位患者生成三个 SABR 计划：常规计划靶区边缘计划、减少边缘计划（大体肿瘤体积 GTV+3mm）和非边缘计划。根据位置，靶区被计划接受 48Gy/4 或 50Gy/5 个分数。根据当地指南，比较了目标覆盖、OAR 剂量和剂量学可接受性。使用逻辑回归分析研究了可接受性的预测因素。
与常规边缘计划相比，减少边缘和非边缘计划几乎都导致所有剂量限制显著降低。非边缘计划的剂量适形性明显较差（P<0.05），与靶区表面积/体积比强烈相关（R=0.9，P<0.05）。减少边缘计划中 26%的计划是可接受的，而非边缘计划中 54%的计划是可接受的。GTV 与 OAR 重叠显著影响计划的可接受性（OR 0.008，95%CI 0.001-0.073）。
减少边缘显著降低了 OAR 剂量，使之前被排除在 SABR 之外的患者能够接受可接受的计划。随着治疗准确性的不断提高，肺 SABR 的适应证可能会扩大；需要进一步研究以确定最有可能受益的患者。
