Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX 75235, United States of America.
Phys Med Biol. 2018 Jun 27;63(13):13NT01. doi: 10.1088/1361-6560/aaca1b.
Particle therapy can achieve excellent dose localization but is sensitive to range uncertainty. Therefore, online in vivo range verification before treatment is critical for treatment safety and quality assurance. We introduce a novel range-probing technique that uses mid-range treatment spots selected from the treatment plan as probing beams to be delivered before other treatment spots in pencil beam scanning. The probing spot signal can be acquired by an in-beam positron emission tomography (PET) scanner, and the reconstructed spot positions are compared with pre-calculated positions to measure the range shift. Mid-range probing ensures that the Bragg peaks stay inside the tumor even with significant range variation from the plan. Single-layered spots enable easier spot detection than multi-layered spots without cross-layered spot smearing. With therapeutic dose, the probing beam offers higher positron activities and range detectability than the low-dose imaging beam by up to two orders of magnitude, without exposing patients to extra radiation. Higher positron activities allow sufficient signal statistics in shorter acquisition time, therefore reducing metabolic washout of positron emitters. Thus, range shifts from the plan can be measured easily. We also describe two online range-compensated plan modification methods. We apply correction, if the range shift is above a certain tolerance. We studied feasibility using simulated particle treatment plans with online anatomical changes. For illustration, we demonstrate range shift measurement using simulated probing dose. The proposed range probing and correction effectively handled range shifts in the simulated cases. Both range-compensated adaptation and optimization accounted for online changes so that the delivered dose matched the planned dose. With a dedicated online in-beam PET scanner and phantom and clinical studies, which are currently being developed, this novel strategy may open up a range-guided particle therapy paradigm.
粒子治疗可以实现极好的剂量定位，但对射程不确定性敏感。因此，在治疗前进行在线体内实时射程验证对于治疗安全和质量保证至关重要。我们引入了一种新的射程探测技术，该技术使用治疗计划中的中程治疗点作为探测束，在铅笔束扫描中先于其他治疗点进行输送。探测点信号可由内置正电子发射断层扫描（PET）扫描仪获取，重建的点位置与预计算的位置进行比较，以测量射程偏移。中程探测确保布拉格峰即使在计划中射程发生显著变化时仍位于肿瘤内。单层点比多层点更容易检测，而不会出现跨层点模糊。用治疗剂量，探测束提供的正电子活动和射程可探测性比低剂量成像束高两个数量级，而不会使患者额外暴露在辐射下。更高的正电子活动允许在更短的采集时间内获得足够的信号统计，从而减少正电子发射体的代谢清除。因此，很容易测量计划中的射程偏移。我们还描述了两种在线射程补偿计划修正方法。如果射程偏移超过一定的容限，我们会进行修正。我们使用带有在线解剖变化的模拟粒子治疗计划来研究其可行性。为了说明问题，我们展示了使用模拟探测剂量进行的射程偏移测量。所提出的射程探测和校正方法有效地处理了模拟病例中的射程偏移。在线补偿的自适应和优化都考虑了在线变化，以便输送的剂量与计划剂量匹配。随着专用的在线内置 PET 扫描仪和体模以及临床研究的开发，这种新策略可能会开创一种基于射程引导的粒子治疗范例。
