Department of Physics and Astronomy, Louisiana State University, Baton Rouge, USA.
Department of Physics and Astronomy, Louisiana State University, Baton Rouge, USA; Department of Radiation Oncology, Mary Bird Perkins Cancer Center, Baton Rouge, USA.
Radiother Oncol. 2020 Aug;149:18-24. doi: 10.1016/j.radonc.2020.04.032. Epub 2020 Apr 24.
Local computed tomography (CT) reconstruction is achievable with portal images acquired during volumetric-modulated arc therapy (VMAT) delivery and was named as VMAT-CT. However, the application of VMAT-CT is limited because it has limited field of view and no density information. In addition, the new generation of multi-leaf collimator with faster speed and various collimator angles used in patients' plans could cause more artifacts in VMAT-CT. The goal of this study was to extend VMAT-CT concept, generate complete three-dimensional (3D) CT images, calculate new 3D dose, track and adapt VMAT plan based on updated images and dose.
VMAT-CT and planning CT of phantoms were fused by rigid or deformable registration to create VMAT-CT+ images. Trackings based on planning CT, VMAT-CT+, and cone beam CT (CBCT) were compared. When prescription dose was not met for planning target volume (PTV), re-planning was demonstrated on an in-house deformable phantom. Possible uncertainties were also evaluated.
Tracking based on VMAT-CT+ was accurate and superior to those based on planning CT and CBCT since VMAT-CT+ can detect changes during treatment. PTV coverage in the deformable phantom decreased after deformations but went up and met the prescription goal after re-planning. The impact of uncertainties on dose was minimal.
3D tracking and adaptation of VMAT based on VMAT-CT are feasible. Our study has the potential to increase the confidence of beam delivery, catch and remedy errors during VMAT.
容积旋转调强放疗（VMAT）治疗过程中采集的射野影像可实现局部计算机断层扫描（CT）重建，被命名为 VMAT-CT。然而，由于其视野有限且没有密度信息，VMAT-CT 的应用受到限制。此外，在患者计划中使用的新一代多叶准直器具有更快的速度和各种准直器角度，可能会在 VMAT-CT 中引起更多伪影。本研究的目的是扩展 VMAT-CT 概念，生成完整的三维（3D）CT 图像，计算新的 3D 剂量，基于更新的图像和剂量进行跟踪和调整 VMAT 计划。
通过刚性或变形配准将体模的 VMAT-CT 和计划 CT 融合，以创建 VMAT-CT+图像。比较了基于计划 CT、VMAT-CT+和锥形束 CT（CBCT）的跟踪。当计划靶区（PTV）未达到规定剂量时，在内部变形体模上演示重新计划。还评估了可能存在的不确定性。
基于 VMAT-CT+的跟踪是准确的，优于基于计划 CT 和 CBCT 的跟踪，因为 VMAT-CT+可以检测治疗过程中的变化。在变形体模中，PTV 覆盖度在变形后降低，但经过重新计划后上升并达到规定目标。不确定性对剂量的影响很小。
基于 VMAT-CT 的 VMAT 的 3D 跟踪和自适应是可行的。我们的研究有可能增加对光束输送的信心，在 VMAT 过程中发现和纠正错误。
