Background: Proton therapy requires caution when treating patients with targets near neural structures. Intuitive and quantitative guidelines are needed to support decision-making concerning the treatment modality. This study compared dosimetric profiles of intensity-modulated proton therapy (IMPT) and intensity-modulated radiation therapy (IMRT) using helical tomotherapy (HT) for adaptive re-planning in cT3-4 nasopharyngeal cancer (NPCa) patients, aiming to establish criteria for selecting appropriate treatment modalities. Methods: HT and IMPT plans were generated for 28 cT3-4 NPCa patients undergoing definitive radiotherapy. Dosimetric comparisons were performed for target coverage and high-priority organs at risk (OARs). The correlation between dosimetric parameters and RT modality selection was analyzed with the target OAR distances. Results: Target coverages were similar, while IMPT achieved better dose spillage. HT was more favorable for brainstem D1, optic chiasm Dmax, optic nerves Dmax, and p-cord D1. IMPT showed advantages for oral cavity Dmean. Actually, 14 IMPT and 14 HT plans were selected as adaptive plans, with IMPT allocated to most cT3 patients (92.9% vs. 42.9%,p= 0.013). The shortest distances from the target to neural structures were negatively correlated with OAR doses. Receiver operating characteristic curve analyses were carried out to discover the optimal cut-off values of the shortest distances between the target and the OARs (temporal lobes and brainstem), which were 0.75 cm (AUC = 0.908, specificity = 1.00) and 0.85 cm (AUC = 0.857, specificity = 0.929), respectively. Conclusions: NPCa patients with cT4 tumor or with the shortest distance between the target and critical neural structures < 0.8 cm were suboptimal candidates for IMPT adaptive re-planning. These criteria may improve resource utilization and clinical outcomes.
背景：质子治疗在靶区邻近神经结构的患者中需谨慎应用，亟需直观且量化的指导原则以支持治疗模式决策。本研究比较了调强质子治疗（IMPT）与螺旋断层放疗（IMRT）在cT3-4期鼻咽癌患者自适应再计划中的剂量学特征，旨在建立适宜治疗模式的选择标准。方法：对28例接受根治性放疗的cT3-4期鼻咽癌患者分别制定HT与IMPT计划，从靶区覆盖度及高危危及器官（OARs）两方面进行剂量学比较，并分析剂量学参数与放疗模式选择及靶区-OAR距离的相关性。结果：两种技术靶区覆盖度相近，但IMPT的剂量外溢控制更优。HT在脑干D1、视交叉Dmax、视神经Dmax及脊髓D1方面更具优势，而IMPT在口腔平均剂量方面表现更佳。实际临床选择中，14例采用IMPT、14例采用HT作为自适应计划，其中IMPT更多应用于cT3期患者（92.9% vs. 42.9%，p=0.013）。靶区与神经结构的最短距离与OAR受照剂量呈负相关。通过受试者工作特征曲线分析发现，靶区与颞叶、脑干的最短距离最佳临界值分别为0.75 cm（曲线下面积=0.908，特异度=1.00）和0.85 cm（曲线下面积=0.857，特异度=0.929）。结论：cT4期肿瘤或靶区与关键神经结构最短距离<0.8 cm的鼻咽癌患者不适宜作为IMPT自适应再计划的首选对象。该标准有望优化医疗资源配置并改善临床疗效。
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