Kim Joshua, Wu Qixue, Zhao Bo, Wen Ning, Ajlouni Munther, Movsas Benjamin, Chetty Indrin J
Department of Radiation Oncology, Henry Ford Health System, 2799 W. Grand Blvd, Detroit, MI, 48202, USA.
Radiat Oncol. 2016 Sep 22;11(1):125. doi: 10.1186/s13014-016-0699-2.
To compare retrospectively generated gated plans to conventional internal target volume (ITV)-based plans and to evaluate whether gated radiotherapy provides clinically relevant dosimetric improvements to organs-at-risk (OARs).
Evaluation was performed of 150 stereotactic ablative radiotherapy treatment plans delivered to 128 early-stage (T1-T3 (<5 cm)) NSCLC patients. To generate gated plans, original ITV-based plans were re-optimized and re-calculated on the end-exhale phase and using gated planning target volumes (PTV). Gated and ITV-based plans were produced for 3 × 18 Gy and 4 × 12 Gy fractionation regimens. Dose differences between gated and ITV-based plans were analyzed as a function of both three-dimensional motion and tumor volume. OARs were analyzed using RTOG and AAPM dose constraints.
Differences between gated and ITV-based plans for all OAR indices were largest for the 3 × 18 Gy regimen. For this regimen, MLD differences calculated by subtracting the gated values from the ITV-based values (ITV vs. Gated) were 0.10 ± 0.56 Gy for peripheral island (N = 57), 0.16 ± 0.64 Gy for peripheral lung-wall seated (N = 57), and 0.10 ± 0.64 Gy for central tumors (N = 36). Variations in V20 were similarly low, with the greatest differences occurring in peripheral tumors (0.20 ± 1.17 %). Additionally, average differences (in 2Gy-equivalence) between ITV and gated lung indices fell well below clinical tolerance values for all fractionation regimens, with no clinically meaningful differences observed from the 4 × 12 Gy regimen and rarely for the 3 × 18 Gy regimen (<2 % of cases). Dosimetric differences between gated and ITV-based methods did generally increase with increasing tumor motion and decreasing tumor volume. Dose to ribs and bronchial tree were slightly higher in gated plans compared to ITV-based plans and slightly lower for esophagus, heart, spinal cord, and trachea.
Analysis of 150 SABR-based lung cancer treatment plans did not show a substantial benefit for the gating regimen when compared to ITV-based treatment plans. Small benefits were observed only for the largest tumor motion (exceeding 2 cm) and the high dose treatment regimen (3 × 18 Gy), though these benefits did not appear to be clinically relevant.
回顾性比较门控计划与传统基于内部靶区（ITV）的计划，并评估门控放疗是否能为危及器官（OARs）带来临床相关的剂量学改善。
对128例早期（T1 - T3（<5 cm））非小细胞肺癌（NSCLC）患者的150个立体定向消融放疗治疗计划进行评估。为生成门控计划，基于原始ITV的计划在呼气末相并使用门控计划靶区（PTV）进行重新优化和重新计算。针对3×18 Gy和4×12 Gy分割方案生成门控计划和基于ITV的计划。分析门控计划与基于ITV的计划之间的剂量差异与三维运动和肿瘤体积的关系。使用RTOG和AAPM剂量限制对OARs进行分析。
对于所有OAR指标，门控计划与基于ITV的计划之间的差异在3×18 Gy分割方案中最大。对于该分割方案，通过从基于ITV的值中减去门控值计算得到的平均剂量差异（ITV与门控），外周岛状肿瘤（N = 57）为0.10±0.56 Gy，外周肺壁附着肿瘤（N = 57）为0.16±0.64 Gy，中央肿瘤（N = 36）为0.10±0.64 Gy。V20的变化同样较小，最大差异出现在外周肿瘤（0.20±1.17%）。此外，对于所有分割方案，ITV与门控肺指标之间的平均差异（以2 Gy等效剂量计）远低于临床耐受值，4×12 Gy分割方案未观察到临床显著差异，3×18 Gy分割方案也很少出现（<2%的病例）。门控方法与基于ITV的方法之间的剂量学差异通常随肿瘤运动增加和肿瘤体积减小而增大。与基于ITV的计划相比，门控计划中肋骨和支气管树的剂量略高，而食管、心脏、脊髓和气管的剂量略低。
与基于ITV的治疗计划相比，对150个基于立体定向消融放疗（SABR）的肺癌治疗计划的分析未显示门控方案有实质性益处。仅在最大肿瘤运动（超过2 cm）和高剂量治疗方案（3×18 Gy）中观察到小的益处，尽管这些益处似乎与临床无关。
