Four-dimensional IMRT treatment planning using a DMLC motion-tracking algorithm

Abstract

The purpose of this study is to develop a four-dimensional (4D) intensity-modulated radiation therapy (IMRT) treatment-planning method by modifying and applying a dynamic multileaf collimator (DMLC) motion-tracking algorithm. The 4D radiotherapy treatment scenario investigated is to obtain a 4D treatment plan based on a 4D computed tomography (CT) planning scan and to have the delivery flexible enough to account for changes in tumor position during treatment delivery. For each of 4D CT planning scans from 12 lung cancer patients, a reference phase plan was created; with its MLC leaf positions and three-dimensional (3D) tumor motion, the DMLC motion-tracking algorithm generated MLC leaf sequences for the plans of other respiratory phases. Then, a deformable dose-summed 4D plan was created by merging the leaf sequences of individual phase plans. Individual phase plans, as well as the deformable dose-summed 4D plan, are similar for each patient, indicating that this method is dosimetrically robust to the variations of fractional time spent in respiratory phases on a given 4D CT planning scan. The 4D IMRT treatment-planning method utilizing the DMLC motion-tracking algorithm explicitly accounts for 3D tumor motion and thus hysteresis and nonlinear motion, and is deliverable on a linear accelerator.

The first patient treatment of electromagnetic-guided real time adaptive radiotherapy using MLC tracking for lung SABR

“…The patient in this study benefited from real-time adaptive treatment with a 41% smaller target volume, which is comparable to that reported for adaptive delivery with robotic and gimbal devices [11,12]. The extent of motion was significantly larger at treatment compared to that seen during 4DCT acquisition.…”

“…Another real-time image guidance and adaption technique, electromagnetic (EM) guided MLC tracking, is expected to match reductions in treated volumes to robotic and gimbal modalities [11,12]. MLC tracking began treating prostate cancer patients in 2013 [13] and demonstrated high fidelity of delivered dose, including dose painting, to moving targets [14].…”

Four‐dimensional intensity‐modulated radiation therapy planning for dynamic tracking using a direct aperture deformation (DAD) method

“…Suh et al 20,32 proposed to shift the aperture position based on the translation of the target centroids, without considering the complexity of respiration related target motion, such as deformation. In our study, we employed a direct aperture deformation algorithm called SAM that can account for both rigid translational motion and nonrigid motion, resulting in better 4D plans.…”

“…One way is to only consider the rigid translation of the target by shifting the aperture position according to the translation of the centroid of the target. 32 However, this scheme ignores the significant complexities [23][24][25] of respiratory-induced target movement and may lead to suboptimal plan quality. In this study, we adopted a DAD method 21,26 that directly modifies the aperture positions and shapes according to the geometric variation in the target.…”

“…They incorporated both target motion and MLC mechanical constraints into the optimization process, requiring massive computational power and specially designed software. A simpler 4D planning method was proposed by Suh et al 20,32 in which rigid translation of the target was considered based on 4DCT; however, in their work, no nonlinear motion or deformation of the target was accounted for.…”