Algorithm-based gantry angle range determination in volumetric modulated arc therapy for liver stereotactic body...

To develop an algorithm-based method for determining optimal gantry angle ranges in volumetric modulated arc therapy (VMAT) for liver cancer by minimizing the beam path length through normal liver.

Fifteen consecutive patients with primary liver cancer who had undergone stereotactic body radiotherapy (SBRT) were analyzed. The algorithm calculated the shortest beam paths between the liver surface and the target center from DICOM-based contours to determine feasible gantry-angle ranges. For each patient, three VMAT plans were generated: (1) an automated gantry-angle plan using the proposed method, (2) an expert manual plan, and (3) a novice manual plan. Plans were compared in terms of selected gantry angle ranges, liver path length, dose-volume parameters, and monitor units (MUs). Gantry angle range agreement between plans was evaluated using the Jaccard similarity coefficient.

The automated plan achieved a mean normal liver path length of 35.0 ± 14.4 mm, comparable to the expert plan (34.6 ± 15.0 mm) and shorter than the novice plan (39.3 ± 15.2 mm), with no significant differences among the three plans (p > 0.05). The mean Jaccard similarity coefficients were 0.86 ± 0.10 (auto-expert) and 0.80 ± 0.12 (auto-novice), indicating closer agreement with expert plans. Dosimetric parameters and MUs were similar across all plans.

The algorithmic approach provides a simple, quantitative, and reproducible method for determining gantry-angle ranges in liver VMAT. It effectively reproduces expert planner decision-making, reduces variability between planners, and has the potential to standardize gantry angle determination and streamline treatment planning.