Aymane Khouya, Alina Santiago, Toke Ringbaek, Nika Guberina, Maja Guberina, Thomas Gauler, Wolfgang Lübcke, Waldemar Zylka, Christoph Pöttgen, Martin Stuschke
Department of Radiotherapy, West German Cancer Center, University Hospital Essen, Hufelandstraße 55, 45147, Essen, Germany.
Faculty of Physical Engineering, Westphalian University, Campus Gelsenkirchen, Neidenburger Str. 43, 45897, Gelsenkirchen, Germany.
Radiat Oncol. 2025 May 15;20(1):75. doi: 10.1186/s13014-025-02656-1.
The Acuros XB dose calculation algorithm implements advanced modelling of lateral electron transport, making dose distributions sensitive to density changes between source and subsequent CT. The aim of this study was to analyse the robustness of dose distribution in the central bronchial wall (CBW) of treatment plans from lung cancer patients treated with adaptive radiotherapy.
IMRT or VMAT plans from patients with locally advanced lung cancer from a prospective registry cohort were analysed, who received definitive radiotherapy in surface-guided inspiratory breath-hold on the Ethos™ closed-bore linac, equipped with the HyperSight™ cone beam CT (CBCT). Dose homogeneity of the scheduled plans, optimized on planning CT (CTplan), was verified on the initial CBCT of a dose fraction (CBCT1). The adaptive plans were verified on a subsequent post-adaptation CBCT (CBCT2) of the same dose fraction. A predictive model was built for maximum dose (Dmax) in CBW in dependence on plan sensitivity in the central bronchial air lumen overlapping the planning target volume (CBAL) to water override (WOR) of the air lumen.
Ninety-one dose-fractions from 10 patients were analysed. Dmax values in the CBW of the scheduled plans showed over all significant inter-fractional increases from CTplan to subsequent CBCT1 (p < 0.0001, Wilcoxon test, stratified by patient) with significant heterogeneity between patients (p < 0.0001, Kruskal-Wallis Test). The median Dmax increase per dose fraction was 2.15% (-3.15 - 19.30%). Reducing the PTV overlap of scheduled plans with CBAL led to lower inter-fractional Dmax increases in CBW (p < 0.0001, signed rank test). Dose accumulation showed, that Dmax and D1cc values in CBW over the treatment course stayed in all patients below 110.5% and 107.5% and that the equivalent uniform dose in CTV around the CBW stayed > 95% for scheduled plans. A predictive model showed the dependence of inter-fractional Dmax increases in CBW of scheduled plans on an interaction between plan sensitivity on CTplan to WOR in CBAL and density change at the Dmax point in CBCT1 between CTplan and CBCT1 (p < 0.0001, t-test). Intra-fractional Dmax increases of adaptive plans in CBW amounted to only 20% +/- 1.1% of the inter-fractional increases of scheduled plans, as intra-fractional deformations were smaller than inter-fractional (p < 0.0001, signed rank test).
Dose homogeneity in CBW of Ethos plans were found sufficiently robust against intra-fractional deformations during course of online adaptive radiotherapy. Plan sensitivity to anatomic changes can be detected and controlled on the planning CT by the WOR of air in CBAL.
Acuros XB剂量计算算法实现了横向电子传输的高级建模，使剂量分布对源与后续CT之间的密度变化敏感。本研究的目的是分析接受自适应放疗的肺癌患者治疗计划中中央支气管壁（CBW）剂量分布的稳健性。
分析了来自前瞻性登记队列的局部晚期肺癌患者的调强放疗（IMRT）或容积调强弧形放疗（VMAT）计划，这些患者在配备HyperSight™锥形束CT（CBCT）的Ethos™封闭孔径直线加速器上进行表面引导吸气屏气下的根治性放疗。在计划CT（CTplan）上优化的预定计划的剂量均匀性在剂量分割的初始CBCT（CBCT1）上进行验证。自适应计划在同一剂量分割的后续适应后CBCT（CBCT2）上进行验证。建立了一个预测模型，用于根据与计划靶体积重叠的中央支气管气腔（CBAL）对气腔水等效物（WOR）的计划敏感性来预测CBW中的最大剂量（Dmax）。
分析了10例患者的91个剂量分割。预定计划的CBW中的Dmax值在从CTplan到后续CBCT1的所有分割间均显示出显著增加（p < 0.0001，Wilcoxon检验，按患者分层），患者之间存在显著异质性（p < 0.0001，Kruskal-Wallis检验）。每个剂量分割的Dmax中位数增加为2.15%（-3.15 - 19.30%）。减少预定计划与CBAL的计划靶体积重叠导致CBW中分割间Dmax增加较低（p < 0.0001，符号秩检验）。剂量累积显示，在整个治疗过程中，所有患者CBW中的Dmax和D1cc值均低于110.5%和107.5%，并且预定计划中CBW周围临床靶体积的等效均匀剂量保持> 95%。一个预测模型显示预定计划的CBW中分割间Dmax增加依赖于CTplan上对CBAL中WOR的计划敏感性与CTplan和CBCT1之间CBCT1中Dmax点处的密度变化之间的相互作用（p < 0.0001，t检验）。CBW中自适应计划的分割内Dmax增加仅为预定计划分割间增加的20% +/- 1.1%，因为分割内变形小于分割间变形（p < 0.0001，符号秩检验）。
发现在线自适应放疗过程中，Ethos计划的CBW中的剂量均匀性对分割内变形具有足够的稳健性。通过CBAL中空气的WOR可以在计划CT上检测和控制计划对解剖变化的敏感性。
