Erasmus MC Cancer Institute, University Medical Center Rotterdam, Department of Radiotherapy, Rotterdam, the Netherlands; Department of Medical Physics & Informatics, HollandPTC, Delft, the Netherlands.
Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands.
Radiother Oncol. 2023 Sep;186:109729. doi: 10.1016/j.radonc.2023.109729. Epub 2023 Jun 8.
In the Netherlands, head-and-neck cancer (HNC) patients are referred for proton therapy (PT) through model-based selection (MBS). However, treatment errors may compromise adequate CTV dose. Our aims are: (i) to derive probabilistic plan evaluation metrics on the CTV consistent with clinical metrics; (ii) to evaluate plan consistency between photon (VMAT) and proton (IMPT) planning in terms of CTV dose iso-effectiveness and (iii) to assess the robustness of the OAR doses and of the risk toxicities involved in the MBS.
Sixty HNC plans (30 IMPT/30 VMAT) were included. A robustness evaluation with 100,000 treatment scenarios per plan was performed using Polynomial Chaos Expansion (PCE). PCE was applied to determine scenario distributions of clinically relevant dosimetric parameters, which were compared between the 2 modalities. Finally, PCE-based probabilistic dose parameters were derived and compared to clinical PTV-based photon and voxel-wise proton evaluation metrics.
Probabilistic dose to near-minimum volume v = 99.8% for the CTV correlated best with clinical PTV-D and VWmin-D doses for VMAT and IMPT respectively. IMPT showed slightly higher nominal CTV doses, with an average increase of 0.8 GyRBE in the median of the D distribution. Most patients qualified for IMPT through the dysphagia grade II model, for which an average NTCP gain of 10.5 percentages points (%-point) was found. For all complications, uncertainties resulted in moderate NTCP spreads lower than 3 p.p. on average for both modalities.
Despite the differences between photon and proton planning, the comparison between PTV-based VMAT and robust IMPT is consistent. Treatment errors had a moderate impact on NTCPs, showing that the nominal plans are a good estimator to qualify patients for PT.
在荷兰，头颈部癌症（HNC）患者通过基于模型的选择（MBS）被推荐接受质子治疗（PT）。然而，治疗误差可能会影响CTV 的充分剂量。我们的目的是：（i）得出与临床指标一致的 CTV 概率性计划评估指标；（ii）评估光子（VMAT）和质子（IMPT）计划在 CTV 剂量等效应方面的计划一致性；（iii）评估 OAR 剂量的稳健性以及 MBS 中涉及的风险毒性。
纳入 60 例 HNC 计划（30 例 IMPT/30 例 VMAT）。使用多项式混沌扩展（PCE）对每个计划进行了 100,000 个治疗场景的稳健性评估。PCE 用于确定临床相关剂量参数的场景分布，并比较两种模式之间的差异。最后，基于 PCE 的概率剂量参数被推导出来，并与临床 PTV 基于光子的评估指标和体素质子评估指标进行比较。
CTV 接近最小体积 v = 99.8%的概率性剂量与 VMAT 和 IMPT 分别的临床 PTV-D 和 VWmin-D 剂量相关性最好。IMPT 显示出稍高的名义 CTV 剂量，在 D 分布的中位数处平均增加了 0.8 GyRBE。大多数患者通过吞咽困难等级 II 模型有资格接受 IMPT，在此模型下平均发现 NTCP 增益为 10.5 个百分点（%-point）。对于所有并发症，不确定性导致两种模式的 NTCP 分布差异适度，平均低于 3 个百分点（p.p.）。
尽管光子和质子计划之间存在差异，但基于 PTV 的 VMAT 和稳健的 IMPT 之间的比较是一致的。治疗误差对 NTCP 有中度影响，表明名义计划是为患者提供 PT 资格的良好估计。
