Background/Objectives: Traditionally, proton therapy assumes a fixed relative biological effectiveness (RBE) value of 1.1, which can lead to inaccurate dose calculations in treatment planning. This study examines the effect of dynamic arc delivery and pencil beam scanning (PBS) linear energy transfer (LET) optimization on LET-dependent RBE dose escalation to nervous tissue structures in head and neck (H&N) cancer patients undergoing proton beam therapy, utilizing two RBE dose models.Methods: Fifteen head and neck cancer patients previously treated with PBS proton therapy at high risk of nervous tissue toxicity were retrospectively analyzed. Three plans were developed for each patient: PBS, dynamic arc, and PBS with LET optimization. RBE-weighted dose distributions were calculated and compared for all patient plans using a linear LET-weighted model and a tissue-specific α/β-dependent model. LET-dose (LETd) constraints were systematically tested to determine optimal values for plan quality and efficacy in altering LET spatial distribution in regions of concern. LET-dependent RBE enhancement was calculated for the three different planning methods.Results: Dynamic arc plans increased RBE enhancement when compared to PBS, while LET optimization for PBS consistently reduced RBE-enhanced dose to nervous tissue compared to non-optimized plans for both RBE models. Patient-specific variability in optimization benefit was observed, with the most significant improvements in cases with greater initial RBE enhancement. A maximum LETdconstraint of 2.5 µm/keV above 80% of the maximum structure dose threshold was found to balance plan quality and RBE mitigation.Conclusions: Dynamic arc delivery increased RBE enhancement relative to static PBS. LET optimization successfully modified LETdspatial distributions to minimize RBE enhancement to nervous tissue structures when compared to non-LET optimized PBS and dynamic arc plans. Patient-specific risk stratification should be used when clinically deploying LET optimization.
背景/目的：传统质子治疗采用固定的相对生物效能（RBE）值1.1，可能导致治疗计划中的剂量计算不准确。本研究采用两种RBE剂量模型，探讨动态弧照射与笔形束扫描（PBS）线性能量转移（LET）优化对头颈部癌症患者质子束治疗中神经组织结构LET依赖性RBE剂量提升的影响。 方法：回顾性分析了15例既往接受PBS质子治疗且神经组织毒性高风险的头颈部癌症患者。为每位患者制定三种计划：PBS计划、动态弧计划及LET优化PBS计划。采用线性LET加权模型和组织特异性α/β依赖模型，计算并比较所有患者计划的RBE加权剂量分布。系统测试LET-剂量（LETd）约束条件，以确定在关注区域改变LET空间分布时计划质量与疗效的最佳平衡值。计算了三种不同计划方法的LET依赖性RBE增强效应。 结果：与PBS计划相比，动态弧计划增加了RBE增强效应；而采用两种RBE模型评估时，LET优化PBS计划相较于未优化计划持续降低了神经组织的RBE增强剂量。优化效果存在患者个体差异性，在初始RBE增强效应更显著的病例中改善最为明显。研究发现，将最大结构剂量阈值80%以上的LETd约束上限设定为2.5 µm/keV，可在计划质量与RBE缓解之间取得最佳平衡。 结论：相较于静态PBS照射，动态弧照射增加了RBE增强效应。与未进行LET优化的PBS及动态弧计划相比，LET优化成功改变了LETd空间分布，从而最小化神经组织结构的RBE增强效应。临床实施LET优化时应采用个体化风险分层策略。
肿瘤(癌症)患者之家