Evaluation of Surface-Guided Breath-Hold for Motion Control In CBCT-Guided Online Adaptive Radiotherapy
Abstract
Purpose
CBCT-based online adaptive radiotherapy (CBCT-oART) enables daily plan adaptation but is sensitive to intra-fraction motion during extended adaptive workflows. This study evaluates breath-hold (BH) motion stability and workflow impact using an in-bore surface-guided radiotherapy (SGRT) system for breast and abdominal lymphoma adaptive treatments.
Methods
Ten whole-breast and ten abdominal lymphoma patients were treated using BH with an in-bore SGRT system on a CBCT-guided oART platform (Ethos, Varian). A total of 49 breast and 65 abdominal lymphoma fractions were analyzed. Translational couch shifts from pre-treatment and mid-treatment CBCTs, referenced to the planning CBCT, were recorded along the LR, AP, and SI axes. A 3 mm SGRT action threshold was used with manual beam hold during both CBCT acquisition and treatment delivery. Setup, beam delivery, and total session times were compared between BH treatments and corresponding free-breathing (FB) cohorts (50 breast and 53 lymphoma fractions).
Results
For breast treatments, mean mid-treatment shifts were 0.77 ± 1.01 mm (LR), 0.91 ± 0.95 mm (AP), and 0.89 ± 1.04 mm (SI), with a maximum shift of 5.1 mm. For abdominal lymphoma, mean mid-treatment shifts were 0.83 ± 1.10 mm (LR), 0.79 ± 1.19 mm (AP), and 0.81 ± 1.09 mm (SI), with a maximum shift of 5.7 mm. Pre-treatment shifts were larger and corrected prior to delivery. For breast patients, setup time was similar between FB and BH workflows (11 ± 4 min vs 11 ± 5 min), while total session time increased slightly (58 ± 12 min vs 62 ± 9 min). For lymphoma patients, beam delivery time increased with BH (11 ± 4 min vs 16 ± 5 min), whereas total session time remained similar (56 ± 18 min vs 58 ± 13 min).
Conclusion
In-bore surface-guided breath-hold demonstrates stable intra-fraction motion with minimal impact on workflow efficiency for CBCT-oART.