Optimal gating envelope size for automatic gating in magnetic resonance imaging-guided radiotherapy.

PURPOSE: This study aimed to investigate the optimal gating envelope (GE) size for automatic gating in magnetic resonance imaging-guided radiotherapy (MRIgRT) for liver cancer.

METHODS

This study retrospectively analyzed imaging and radiation treatment data from ten patients with liver cancer who underwent MRIgRT. Three different GE sizes, covering 7, 5, and 3 out of 10 respiratory phases, referred to as 7-, 5-, and 3-phase GEs, respectively, were used to assess the gating treatment method for this patient cohort, in addition to the internal target volume-based treatment approach. MRIgRT treatment plans were created for each of the motion management techniques, and the resulting dosimetric quality was compared between the plans. A vendor-provided motion analysis software was used to calculate tumor motion trajectories and treatment efficiency.

RESULTS

Compared to the ITV-based treatment plan, the average dose reductions were 8.2 %, 13.1 %, and 15.4 % for 7-, 5-, and 3-phase GEs. Small GE significantly reduced mean liver dose and OAR exposure in patients with a GTV of 50-100 cm3 and a minimum GTV-to-OAR distance of < 1 cm. Conversely, larger GE enabled higher beam-on ratios with acceptable dose constraints in patients with a smaller GTV and a greater anatomical separation. A significant correlation between GTV-to-OAR distance and normalized OAR dose was observed.

CONCLUSIONS

This study revealed the clinical potential of individualized gating strategies informed by real-time motion analysis. Personalized GE optimization may improve precision and organ sparing and reduce treatment time in MRIgRT for liver cancer.