Author: Eva Lee, R. Lee MacDonald, Alasdair Syme, Christopher G. Thomas đ¨âđŹ
Affiliation: Department of Radiation Oncology, QE2 Cancer Centre, Nova Scotia Health, Dalhousie University, Nova Scotia Health đ
Purpose:
Dynamic couch rotation in radiotherapy offers dosimetric benefits, however patient comfort remains a concern. This study investigates couch kinematics in trajectory-based radiotherapy plans, combining VMAT and intra-arc binary collimation (iABC), which enable variable couch speeds between control points (CPs). The goal is to guide treatment optimization while improving patient experience.
Methods:
Six VMAT plans were replanned using the combined optimization of dynamic axes (CODA) technique to generate dynamic gantry, couch, and collimator trajectories. For each VMAT plan, two dynamic plans were generated: CODA-VMAT (one gantry arc and 4â6 couch arcs) and CODA-iABC (one gantry arc and two couch arcs). Gantry arcs enabled bi-directional couch rotation, whereas couch arcs required continuous unidirectional rotation. Plans were delivered on a Varian TrueBeam accelerator. Couch angular velocity was recorded using an accelerometer (Xsens MTw Awinda), and acceleration was calculated. Plans were evaluated based on couch kinematics, plan quality, beam-on-time (BOT), and delivery accuracy.
Results:
Angular speed and acceleration ranged from 0.5 to 2.5°/s and 0.5 to 6°/s², respectively. Gantry arcs predominantly operated at lower speeds (<1.5°/s) and accelerations (<3°/s²), with greater variability observed during couch arcs. CODA-VMAT plans (comparable to VMAT plans, BOT = 357 s) spent 76% and 79% of treatment time at <1.5°/s and <3°/s², respectively, suggesting greater patient comfort. In contrast, CODA-iABC plans (superior VMAT plans, BOT = 462 s) exhibited higher speeds and accelerations, with 41% and 37% of treatment time spent at >1.5°/s and >3°/s², reflecting a trade-off for potentially greater plan quality. For reference, 1.5°/s is comparable to motorized recliners, and 3°/s² is similar to sit-stand desks or motorized vehicle seat accelerations.
Conclusion:
This study highlights a trade-off between plan quality and time spent at low-speed/acceleration regions, offering insights into acceptable limits for dynamic motion in radiotherapy. Future work will explore correlations between acceleration and patient comfort.