Enhancing Estimation Accuracy of Prostate Cancer VMAT Planning: A Knowledge-based Approach Using Multiple Collimator Angles

Background/Aim: This study aimed to determine whether a knowledge-based planning model incorporating treatment plans with multiple collimator angles (Multi-coll. model) provides superior estimation accuracy and plan quality for a range of collimator angles compared with a typical institutional model (Inst. model). Materials and Methods: Five institutions using volumetric modulated arc therapy for prostate cancer participated in the study. The Inst. model comprised plans using a fixed collimator angle, whereas the Multi-coll. model registered plans using single arcs and collimator angles of 10°, 30°, 50°, and 70°. The coefficient of determination and mean squared error were calculated, and the estimation accuracy and dosimetric results for three validation cases at each institution were compared for each model. Dosimetric parameters included volumes receiving at least 20%, 50%, and 90% of the prescription dose (V₂₀, V₅₀, and V₉₀, respectively) at each collimator angle. Results: The Multi-coll. model yielded a higher coefficient of determination and lower mean squared error than the Inst. model, although overfitting of data was a concern at two institutions. The mean absolute errors between estimated and calculated values were (Inst. model vs. Multi-coll. model): 4.41% vs. 2.60% (V₂₀), 4.03% vs. 2.27% (V₅₀), and 2.07% vs. 1.09% (V₉₀) for the rectum; 3.48% vs. 3.42% (V₂₀), 2.24% vs. 3.65% (V₅₀), and 1.11% vs. 0.73% (V₉₀) for the bladder. The Multi-coll. model exhibited a lower rectal and vesical V₂₀ than the Inst. model. Conclusion: The Multi-coll. model had a greater estimation accuracy and slightly higher plan quality than the Inst. model.