Department of Clinical Oncology, TuenMun Hospital, Hong Kong, SAR, China.
Department of Radiotherapy, West German Cancer Center, University Hospital Essen, University of Duisburg-Essen, Hufelandstraße 55, 45147, Essen, Germany.
Radiat Oncol. 2020 May 29;15(1):130. doi: 10.1186/s13014-020-01573-9.
PTV concept is presumed to introduce excessive and inconsistent GTV dose in lung stereotactic body radiotherapy (SBRT). That GTV median dose prescription (D) and robust optimization are viable PTV-free solution (ICRU 91 report) to harmonize the GTV dose was investigated by comparisons with PTV-based SBRT plans.
Thirteen SBRT plans were optimized for 54 Gy / 3 fractions and prescribed (i) to 95% of the PTV (D) expanded 5 mm from the ITV on the averaged intensity project (AIP) CT, i.e., PTV, (ii) to D of PTV derived from the van Herk (VH)'s margin recipe on the mid-ventilation (MidV)-CT, i.e., PTV, (iii) to ITV D by worst case scenario (WCS) optimization on AIP,i.e., WCS and (iv) to GTV D by WCS using all 4DCT images, i.e., WCS. These plans were subsequently recalculated on all 4DCT images and deformably summed on the MidV-CT. The dose differences between these plans were compared for the GTV and selected normal organs by the Friedman tests while the variability was compared by the Levene's tests. The phase-to-phase changes of GTV dose through the respiration were assessed as an indirect measure of the possible increase of photon fluence owing to the type-B dose engine. Finally, all plans were renormalized to GTV D and all the dosimetric analyses were repeated to assess the relative influences of the SBRT planning concept and prescription method on the variability of target dose.
By coverage prescriptions (i) to (iv), significantly smaller chest wall volume receiving ≥30 Gy (CW) and normal lung ≥20 Gy (NL) were achieved by WCS and WCS compared to PTV and PTV (p > 0.05). These plans differed significantly in the recalculated and summed GTV D, D and D (p < 0.05). The inter-patient variability of all GTV dose parameters is however equal between these plans (Levene's tests; p > 0.05). Renormalizing these plans to GTV D reduces their differences in GTV D, and D to insignificant level (p > 0.05) and their inter-patient variability of all GTV dose parameters. None of these plans showed significant differences in GTV D, D and D between respiratory phases, nor their inter-phase variability is significant.
Inconsistent GTV dose is not unique to PTV concept but occurs to other PTV-free concept in lung SBRT. GTV D renormalization effectively harmonizes the target dose among patients and SBRT concepts of geometric uncertainty management.
PTV 概念被认为会在肺部立体定向体部放射治疗（SBRT）中引入过度且不一致的 GTV 剂量。通过与基于 PTV 的 SBRT 计划进行比较，研究了 GTV 中位数剂量处方（D）和稳健优化是否为无 PTV 的可行解决方案（ICRU 91 报告），以协调 GTV 剂量。
对 54Gy/3 个分次的 13 个 SBRT 计划进行优化，并处方（i）在平均强度项目（AIP）CT 上将 ITV 扩展 5mm 处的 PTV（D）的 95%，即 PTV，（ii）在 MidV-CT 上根据 van Herk（VH）的边界配方得出的 PTV（D），即 PTV，（iii）在 AIP 上通过最坏情况情况（WCS）优化得到的 ITV D，即 WCS，以及（iv）使用所有 4DCT 图像的 GTV D 进行 WCS，即 WCS。这些计划随后在所有 4DCT 图像上重新计算，并在 MidV-CT 上进行可变形求和。通过 Friedman 检验比较这些计划的 GTV 和选定的正常器官之间的剂量差异，而通过 Levene's 检验比较变异性。通过评估 GTV 剂量随呼吸的相位变化，间接评估由于 B 型剂量引擎而导致光子通量增加的可能性。最后，将所有计划重新归一化为 GTV D，并重复所有剂量学分析，以评估 SBRT 计划概念和处方方法对靶区剂量变异性的相对影响。
通过覆盖处方（i）至（iv），与 PTV 和 PTV 相比，WCS 和 WCS 可显著减少胸部壁体积接收≥30Gy（CW）和正常肺体积接收≥20Gy（NL）（p>0.05）。这些计划在重新计算和求和的 GTV D、D 和 D 方面存在显著差异（p<0.05）。然而，这些计划之间所有 GTV 剂量参数的患者间变异性是相等的（Levene's 检验；p>0.05）。将这些计划归一化为 GTV D 可将它们在 GTV D 和 D 方面的差异降低到无显著差异（p>0.05），并将它们所有 GTV 剂量参数的患者间变异性降低到无显著差异。这些计划在 GTV D、D 和 D 方面在呼吸相位之间均无显著差异，其相位间变异性也无显著差异。
不一致的 GTV 剂量并非 PTV 概念所特有，而是发生在肺部 SBRT 中的其他无 PTV 概念中。GTV D 归一化可有效协调患者之间的靶区剂量和 SBRT 几何不确定性管理概念。
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