Pencil beam scanning delivered with continuous scanning has several advantages over conventional discrete spot scanning. Such advantages include improved beam delivery efficiency and reduced beam delivery time. However, a move dose is delivered between consecutive spots with continuous scanning, and current treatment planning systems do not take this into account. Therefore, continuous scanning and discrete spot plans have an inherent dose discrepancy. Using the operating parameters of the state-of-the-art particle therapy system, we conducted a proof-of-concept study in which we systematically generated 28 plans for cubic targets with different combinations of plan parameters and simulated the dose discrepancies between continuous scanning and a planned one. A nomograph to guide the selection of plan parameters was developed to reduce the dose discrepancy. The effectiveness of the nomograph was evaluated with two clinical cases (one prostate and one liver). Plans with parameters guided by the nomograph decreased dose discrepancy than those used standard plan parameters. Specifically, the 2%/2 mm gamma passing rate increased from 96.3% to 100% for the prostate case and from 97.8% to 99.7% for the liver case. The CTV DVH root mean square error decreased from 2.2% to 0.2% for the prostate case and from 1.8% to 0.9% for the liver case. The decreased dose discrepancy may allow the relaxing of the delivery constraint for some cases, leading to greater benefits in continuous scanning. Further investigation is warranted.
与传统离散点扫描相比，采用连续扫描方式的笔形束扫描具有多项优势，包括提升束流投递效率及缩短投递时间。然而，连续扫描在相邻扫描点间会产生移动剂量，而当前治疗计划系统尚未对此进行考量，导致连续扫描与离散点计划间存在固有的剂量差异。本研究基于先进粒子治疗系统的运行参数开展概念验证，通过系统生成28组立方体靶区计划（采用不同参数组合），模拟分析了连续扫描与计划剂量间的差异。为降低剂量差异，研究构建了用于指导计划参数选择的列线图，并通过前列腺与肝脏两例临床病例验证其有效性。结果显示：采用列线图指导参数制定的计划较标准参数计划显著降低了剂量差异。具体而言，前列腺病例的2%/2 mm伽马通过率从96.3%提升至100%，肝脏病例从97.8%提升至99.7%；前列腺病例的CTV剂量体积直方图均方根误差从2.2%降至0.2%，肝脏病例从1.8%降至0.9%。剂量差异的降低可能在某些病例中放宽投递限制条件，从而更充分发挥连续扫描的优势。该方向值得进一步深入研究。
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