Zhao Xiaodong, Zhang Rui
Department of Radiation Oncology, Washington University in St. Louis, St. Louis, Missouri, USA.
Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana, USA.
J Med Phys. 2023 Apr-Jun;48(2):154-160. doi: 10.4103/jmp.jmp_24_23. Epub 2023 Jun 29.
Volumetric modulated arc therapy (VMAT) has been increasingly used for cancer patients due to the fast delivery and improved dose conformity. Adaptive radiotherapy (ART) can significantly decrease dose to normal tissues and allow for dose escalation. However, current imaging techniques cannot provide four-dimensional (4D) patient anatomy or dose information during VMAT, which is critical for ART that involves respiratory motion. A novel imaging tool named VMAT-computed tomography (VMAT-CT) has the potential to reveal intra-fractional patient information. The goal of this study was to evaluate the feasibility of 4D adaptive VMAT based on 4D VMAT-CT.
A commercial QUASAR respiratory phantom and an in-house deformable lung phantom were used in this study, and lung VMAT plans, including 4D union plan and 4D ART plan, were generated for the phantoms. A real lung patient's plan was also used in this feasibility study. ART plans based on 4D VMAT-CT were created for the phantoms and the real patient when planning goals were not met. Dose escalation plan based on 4D VMAT-CT was also created for the real patient.
Planning target volume (PTV) coverage for the QUASAR phantom was 85.5% after breathing pattern being changed, and went up to 95% after adaptive re-planning. PTV coverage for the deformable phantom was 93% after deformation and breathing pattern being changed, and went up to 95% after re-planning. Re-planning and dose escalation were feasible and can spare normal tissues for the real patient. 4D ART plan based on 4D VMAT-CT required smaller margins than 4D union plan while maintaining the same prescription dose coverage.
ART based on 4D VMAT-CT is feasible and would potentially facilitate re-planning and PTV dose escalation for VMAT patients who have the motion issue.
容积调强弧形放疗（VMAT）因其快速投照和改善的剂量适形性，已越来越多地应用于癌症患者。自适应放疗（ART）可显著降低对正常组织的剂量，并允许剂量递增。然而，当前的成像技术无法在VMAT期间提供四维（4D）患者解剖结构或剂量信息，这对于涉及呼吸运动的ART至关重要。一种名为VMAT计算机断层扫描（VMAT-CT）的新型成像工具有可能揭示分次内患者信息。本研究的目的是评估基于4D VMAT-CT的4D自适应VMAT的可行性。
本研究使用了一个商用QUASAR呼吸体模和一个自制的可变形肺部体模，并为这些体模生成了肺部VMAT计划，包括4D联合计划和4D ART计划。一项可行性研究中还使用了一名真实肺部患者的计划。当规划目标未达成时，基于4D VMAT-CT为体模和真实患者创建ART计划。还为真实患者创建了基于4D VMAT-CT的剂量递增计划。
改变呼吸模式后，QUASAR体模的计划靶体积（PTV）覆盖率为85.5%，自适应重新规划后升至95%。可变形体模在变形和改变呼吸模式后PTV覆盖率为93%，重新规划后升至95%。重新规划和剂量递增是可行的，并且可以为真实患者 spared正常组织。基于4D VMAT-CT的4D ART计划在保持相同处方剂量覆盖的同时，所需的边界比4D联合计划小。
基于4D VMAT-CT的ART是可行的，并且可能有助于为有运动问题的VMAT患者进行重新规划和PTV剂量递增。
