摘要
背景：碳离子放射治疗（CIRT）具有更高的线性能量转移（LET）和优越的相对生物学效果，是治疗缺氧、放射耐药肿瘤的一个有希望的选择。点扫描强子弧（SHArc）治疗使肿瘤的平均剂量LET （LETd）上升，但增加了计划和设置的复杂性。由于系统体积大，控制要求复杂，动态输送对于基于龙门架的碳离子弧治疗来说仍然是不切实际的。分步射击递送虽然效率较低，但提供了可行的替代方案，代表了临床SHArc实施的关键步骤。目的：本工作建立了海德堡离子束治疗中心使用龙门架系统进行碳离子弧治疗（静态SHArc）的第一个步进射击计划和递送技术。根据胰腺癌的计划质量和交付可行性评估静态SHArc治疗。方法：对7例胰腺癌患者进行静态SHArc方案优化，考虑20个龙门角度。研究了两种不同的能量层（EL）选择技术：(1)中央EL，选择每束7个中央EL；(2)基于MU的EL，优先考虑贡献最高监测单位（MU）的EL。进行LETd优化，将最小LETd提高到肿瘤总体积内的~ 50-80 keV/µm。使用两个单场优化后斜光束（2-SFO），将静态SHArc计划与常规IMPT进行剂量一致性、LETd以及对设置（5mm）和范围（1.5%）不确定性的鲁棒性比较。通过每日对照CT扫描的前向剂量计算来评估分数间的稳健性。使用重离子龙门架系统进行静态SHArc的剂量学验证和递送时间验证，通过圆柱形PMMA模体中的离子室和薄膜测量进行端到端测试。结果：静态SHArc计划在不影响靶覆盖和临床OAR限制的情况下改善了肿瘤中的LETd分布。基于mu的EL方法增加了最小靶剂量，而中央EL使肿瘤中心的LETd浓度更高。与双sfo相比，静态SHArc的两种能量选择方法都表现出较低的分数间鲁棒性。结论：本研究研究了静态SHArc，一种用于输送碳离子弧治疗的分步射击方法。虽然静态SHArc可以提供剂量学优势，特别是在LETd分布方面，但EL选择起着关键作用。提高分数间的稳健性对临床实施仍然至关重要。Background: Carbon ion radiotherapy (CIRT) offers higher linear energy transfer (LET) and superior relative biological effectiveness, making it a promising option for treating hypoxic, radioresistant tumors. Spot-scanning Hadron Arc (SHArc) therapy enables dose-averaged LET (LETd) escalation in the tumor but increases planning and setup complexity. Dynamic delivery remains impractical for gantry-based carbon ion arc therapy due to the system's large size and complex control requirements. Step-and-shoot delivery, while less efficient, provides a feasible alternative and represents a key step towards clinical SHArc implementation.
Purpose: This work establishes the first step-and-shoot planning and delivery technique for carbon ion arc therapy (static SHArc) at the Heidelberg Ion-beam Therapy Center using the gantry system. Static SHArc therapy is evaluated in terms of plan quality and delivery feasibility for pancreatic cancer.
Methods: Static SHArc plans were optimized for seven pancreatic cancer cases, considering 20 gantry angles. Two distinct energy layer (EL) selection techniques were investigated: (1) Central EL, selecting the seven central ELs per beam, and (2) MU-Based EL, prioritizing ELs contributing the highest monitor units (MU). LETd optimization was performed to escalate the minimum LETd to ∼50-80 keV/µm within the gross tumor volume. Static SHArc plans were compared against conventional IMPT using two single-field optimized posterior oblique beams (2-SFO), in terms of dose conformality, LETd, and robustness against setup (5 mm) and range (1.5%) uncertainties. Inter-fractional robustness was assessed via forward dose calculation on daily control CT scans. Dosimetric validation and delivery time verification for static SHArc using the heavy ion gantry system were conducted via end-to-end testing with ion chamber and film measurements in a cylindrical PMMA phantom.
Results: Static SHArc plans improved LETd distributions in the tumor without compromising target coverage and clinical OAR constraints. The MU-based EL method increased minimum target dose, whereas Central EL enabled higher LETd concentration in the tumor center. Both energy selection methods for static SHArc exhibited reduced inter-fractional robustness compared to the two-SFO. Dosimetric verification showed deviations < 3% and total delivery time was ∼27 min.
Conclusions: This study investigates static SHArc, a step-and-shoot approach for delivering carbon ion arc therapy. While static SHArc can provide dosimetric advantages, particularly in terms of LETd distribution, EL selection plays a key role. Improving inter-fraction robustness remains crucial for clinical implementation.
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