Engwall Erik, Mikhalev Victor, Sundström Johan, Marthin Otte, Wase Viktor
Research and Development, RaySearch Laboratories, Stockholm, Sweden.
Med Phys. 2025 Sep;52(9):e18051. doi: 10.1002/mp.18051.
Upright proton therapy with compact delivery systems has the potential to reduce costs for treatments but could also lead to broadening of the beam penumbra due to energy selection close to the patient.
This study aims at combining upright static proton arcs with additional layers of shoot-through (ST) protons to sharpen the beam penumbra and improve plan quality for such systems. An additional advantage of the method is that it provides a straightforward approach for range verification with a fixed range detector opposite the fixed proton nozzle.
We examined various treatment plans for a virtual phantom: 3-beam IMPT, static arc (Arc) with/without ST (Arc+ST), and with/without collimation (+Coll). In the virtual phantom three different targets were utilized to study the effect on conformity index (CI), homogeneity index (HI), robustness and mean dose to the phantom volume. The phantom study was complemented with a head-and-neck (H&N) patient case with a similar set of plans. The delivery time for all plans was estimated using a combined model of the upright patient positioner and the proton nozzle. A range verification concept that determines residual ranges of the ST protons was studied in simulated scenarios for the H&N case.
In the phantom study, the Arc+ST plans show superior CI, HI and target robustness compared to the Arc+Coll plans. For the Arc plans without ST, the collimated plans perform better than the uncollimated plans. On the other hand, for Arc+ST, collimation has little impact on CI, HI and robustness. However, a small increase in the mean dose to the phantom volume is seen without collimation. For the H&N case, similar improvements for Arc+ST can be seen with only a marginal increase of the mean dose to the patient volume when no collimation is used. These results imply that no aperture is needed when combining arcs with ST, which in turn substantially reduces treatment times: for the H&N case the delivery time for Arc+ST is estimated to 5.4 min and for Arc+Coll to 6.5 min. The range verification simulation shows that the method is sensitive to detect systematic stopping power ratio errors, setup errors and changes in the patient anatomy.
Combining proton arcs and ST layers can enhance compact upright proton solutions by improving plan quality at the same time as delivery time is reduced. The concept is also tailored for the inclusion of a fast and straightforward residual range verification method.
采用紧凑型输送系统的直立式质子治疗有降低治疗成本的潜力，但由于在靠近患者处进行能量选择，也可能导致射束半影变宽。
本研究旨在将直立式静态质子弧与额外的穿透式（ST）质子层相结合，以锐化射束半影并改善此类系统的计划质量。该方法的另一个优点是，它为使用与固定质子喷嘴相对的固定射程探测器进行射程验证提供了一种直接的方法。
我们研究了虚拟体模的各种治疗计划：三束调强质子治疗（IMPT）、有/无ST的静态弧（Arc）以及有/无准直（+Coll）。在虚拟体模中，利用三个不同的靶区来研究对适形指数（CI）、均匀性指数（HI）、鲁棒性以及体模体积平均剂量的影响。体模研究辅以一个具有类似计划集的头颈（H&N）患者病例。使用直立患者定位器和质子喷嘴的组合模型估计所有计划的输送时间。在H&N病例的模拟场景中研究了一种确定ST质子剩余射程的射程验证概念。
在体模研究中，与Arc+Coll计划相比，Arc+ST计划显示出更好的CI、HI和靶区鲁棒性。对于没有ST的Arc计划，准直计划比未准直计划表现更好。另一方面，对于Arc+ST，准直对CI、HI和鲁棒性影响不大。然而，在未准直的情况下，体模体积的平均剂量有小幅增加。对于H&N病例，在不使用准直的情况下，Arc+ST也有类似的改善，患者体积的平均剂量仅略有增加。这些结果表明，将弧与ST相结合时不需要孔径，这反过来大大减少了治疗时间：对于H&N病例，Arc+ST的输送时间估计为5.4分钟，Arc+Coll为6.5分钟。射程验证模拟表明，该方法对检测系统阻止本领比误差、设置误差和患者解剖结构变化很敏感。
结合质子弧和ST层可以通过提高计划质量同时减少输送时间来增强紧凑型直立质子治疗方案。该概念还适用于纳入一种快速且直接的剩余射程验证方法。
