RaySearch Laboratories AB, Stockholm, Sweden.
Phys Med Biol. 2018 May 2;63(9):095006. doi: 10.1088/1361-6560/aabb7b.
Non-small cell lung cancer (NSCLC) is a tumour type thought to be well-suited for proton radiotherapy. However, the lung region poses many problems related to organ motion and can for actively scanned beams induce severe interplay effects. In this study we investigate four mitigating rescanning techniques: (1) volumetric rescanning, (2) layered rescanning, (3) breath-sampled (BS) layered rescanning, and (4) continuous breath-sampled (CBS) layered rescanning. The breath-sampled methods will spread the layer rescans over a full breathing cycle, resulting in an improved averaging effect at the expense of longer treatment times. In CBS, we aim at further improving the averaging by delivering as many rescans as possible within one breathing cycle. The interplay effect was evaluated for 4D robustly optimized treatment plans (with and without rescanning) for seven NSCLC patients in the treatment planning system RayStation. The optimization and final dose calculation used a Monte Carlo dose engine to account for the density heterogeneities in the lung region. A realistic treatment delivery time structure given from the IBA ScanAlgo simulation tool served as basis for the interplay evaluation. Both slow (2.0 s) and fast (0.1 s) energy switching times were simulated. For all seven studied patients, rescanning improves the dose conformity to the target. The general trend is that the breath-sampled techniques are superior to layered and volumetric rescanning with respect to both target coverage and variability in dose to OARs. The spacing between rescans in our breath-sampled techniques is set at planning, based on the average breathing cycle length obtained in conjunction with CT acquisition. For moderately varied breathing cycle lengths between planning and delivery (up to 15%), the breath-sampled techniques still mitigate the interplay effect well. This shows the potential for smooth implementation at the clinic without additional motion monitoring equipment.
非小细胞肺癌（NSCLC）是一种被认为非常适合质子放射治疗的肿瘤类型。然而，肺部区域存在许多与器官运动相关的问题，并且对于主动扫描束，会引起严重的相互作用效应。在这项研究中，我们研究了四种减轻相互作用效应的再扫描技术：（1）体积再扫描，（2）分层再扫描，（3）呼吸采样（BS）分层再扫描，和（4）连续呼吸采样（CBS）分层再扫描。呼吸采样方法将层扫描分布在整个呼吸周期中，从而在治疗时间延长的情况下提高平均效果。在 CBS 中，我们旨在通过在一个呼吸周期内尽可能多地进行扫描来进一步改善平均效果。在 RayStation 治疗计划系统中，我们对七位 NSCLC 患者的 4D 稳健优化治疗计划（包括和不包括再扫描）进行了相互作用效应评估。优化和最终剂量计算使用了蒙特卡罗剂量引擎来考虑肺部区域的密度不均匀性。IBA ScanAlgo 模拟工具提供的现实治疗交付时间结构作为相互作用评估的基础。模拟了两种较慢（2.0 秒）和较快（0.1 秒）的能量切换时间。对于所有七位研究患者，再扫描均可改善靶区剂量一致性。一般趋势是，与分层和体积再扫描相比，呼吸采样技术在靶区覆盖和 OAR 剂量变异性方面均具有优势。我们的呼吸采样技术中的再扫描间隔是在计划阶段根据结合 CT 采集获得的平均呼吸周期长度设置的。对于计划和交付之间呼吸周期长度变化适中（高达 15％）的情况，呼吸采样技术仍能很好地减轻相互作用效应。这表明在没有额外运动监测设备的情况下，在临床中可以实现平稳实施。
