Balancing dose preservation and treatment efficiency in motion-managed magnetic resonance image-guided radiotherapy of pancreatic cancer.

[BACKGROUND AND PURPOSE] Active motion management (AMM) during magnetic resonance image (MRI)-guided pancreatic cancer radioablation enables tight planning target volume (PTV) margins but may prolong treatment. AMM strategies include beam gating and drift correction, which respectively interrupt or adjust treatment delivery in response to target motion. This study evaluates gross tumor volume (GTV) dose coverage and time efficiency using varying AMM settings.

[MATERIALS AND METHODS] Cine MRI data from 100 fractions in 20 patients undergoing MRI-guided pancreatic cancer radioablation were used to simulate treatment delivery of 5 × 10.0 Gy using a 2 mm PTV margin. Seventeen scenarios were evaluated: No AMM and combinations of gating window and drift correction thresholds from 5 mm to 2 mm. Accumulated dose and treatment time efficiency (beam-on/total time) were derived from the simulated beam history.

[RESULTS] Without AMM, the median (5th-95th percentile) change in GTV D was -1.8 (-10.3-1.6) Gy. Lowering the drift threshold to 2 mm while using a 5 mm gating window achieved almost similar GTV dose preservation to a 2 mm gating window with 5 mm drift threshold [-0.9 (-3.9-1.1) Gy vs -0.8 (-3.3-1.2) Gy), but with substantially higher efficiency [90 (69-100) % vs 60 (28-94) %].

[CONCLUSIONS] AMM improved GTV dose fidelity for pancreatic cancer radioablation with tight PTV margins, but stricter motion thresholds reduced efficiency. Prioritizing a low drift threshold over a narrow gating window preserved most of dose-related benefits while maintaining more efficient delivery, and may represent an AMM strategy for clinical workflows.