Clinical experience with free-breathing expiration-gated 10MV FFF VMAT stereotactic lung radiotherapy

Free-breathing expiration-gating (EG) is a non-invasive technique used to manage respiratory-induced tumor motion. This study explores the effectiveness of EG stereotactic body radiotherapy (SBRT) for lung tumors using 10MV FFF VMAT.

The study included 41 patients (50 targets) treated with EG lung SBRT between September 2019 and February 2023. Patients underwent free-breathing uncoached 10-phase 4DCT for planning, with the choice for EG based on e.g. tumor motion, critical organ dose, expected target visibility on free-breathing CBCT, taking into account suitability of the breathing pattern. The gating window was typically set at phases 30-70 % of the breathing cycle. Treatment planning utilized VMAT with 10MV FFF, and tumor motion was monitored using EG-CBCT ± near real-time markerless kV imaging. Treatment times for the different parts of treatment, tumor stability and clinical outcomes were evaluated. Dosimetric outcomes were compared between EG and free-breathing plans for a subset of 10 patients.

EG SBRT substantially reduced longitudinal tumor motion and internal target volume (ITV) by 77 % and 42 % respectively. There was a mean decrease of 21/24 % in V5/V20Gy for the ipsilateral lung. Motion monitoring during treatment for 20 targets showed that intrafraction tumor motion remained within 2 mm for most patients, ensuring accurate dose delivery. 86 % of fractions were completed within 25 min. No local recurrences were observed during a median follow-up of 13 months.

Free-breathing EG SBRT is a feasible, effective, and practical approach for lung cancer treatment, offering significant reductions in tumor motion and lung doses while maintaining high treatment accuracy and acceptable treatment times.