The Pencil Beam Scanning (PBS) technique in modern particle therapy offers a highly conformal dose distribution but poses challenges due to the interplay effect, an interaction between respiration-induced organ movement and PBS. This study evaluates the effectiveness of different volumetric rescanning strategies in mitigating this effect in liver cancer proton therapy. We used a Geant4-based Monte Carlo simulation toolkit, 'TOPAS,' and an image registration toolbox, 'Elastix,' to calculate 4D dose distributions from 5 patients' four-dimensional computed tomography (4DCT). We analyzed the homogeneity index (HI) value of the Clinical Tumor Volume (CTV) at different rescan numbers and treatment times. Our results indicate that dose homogeneity stabilizes at a low point after a week of treatment, implying that both rescanning and fractionation treatments help mitigate the interplay effect. Notably, an increase in the number of rescans doesn't significantly reduce the mean dose to normal tissue but effectively prevents high localized doses to tissue adjacent to the CTV. Rescanning techniques, based on statistical averaging, require no extra equipment or patient cooperation, making them widely accessible. However, the number of rescans, tumor location, diaphragm movement, and treatment fractionation significantly influence their effectiveness. Therefore, deciding the number of rescans should involve considering the number of beams, treatment fraction size, and total delivery time to avoid unnecessary treatment extension without significant clinical benefits. The results showed that 2-3 rescans are more clinically suitable for liver cancer patients undergoing proton therapy.

中文翻译：

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体积重新扫描和分割治疗对肝癌质子治疗剂量均匀性影响的研究。

现代粒子治疗中的笔形束扫描 (PBS) 技术提供了高度适形的剂量分布，但由于相互作用效应（呼吸引起的器官运动与 PBS 之间的相互作用）而带来了挑战。本研究评估了不同的体积重新扫描策略在减轻肝癌质子治疗中的这种影响方面的有效性。我们使用基于 Geant4 的蒙特卡罗模拟工具包“TOPAS”和图像配准工具箱“Elastix”来计算 5 名患者的四维计算机断层扫描 (4DCT) 的 4D 剂量分布。我们分析了不同重新扫描次数和治疗时间下临床肿瘤体积（CTV）的均匀性指数（HI）值。我们的结果表明，治疗一周后剂量均匀性稳定在低点，这意味着重新扫描和分割治疗都有助于减轻相互作用效应。值得注意的是，重新扫描次数的增加并不会显着降低正常组织的平均剂量，但可以有效防止 CTV 附近组织的局部高剂量。基于统计平均的重新扫描技术不需要额外的设备或患者的配合，因此可以广泛使用。然而，重新扫描的次数、肿瘤位置、膈肌运动和治疗分割会显着影响其有效性。因此，决定重新扫描的次数应考虑射束数量、治疗分数大小和总交付时间，以避免不必要的治疗延长而没有显着的临床益处。结果表明，2-3次复查在临床上更适合接受质子治疗的肝癌患者。