Dosimetric Evaluation of Simplified Knowledge-Based Plan with an Extensive Stepping Validation Approach in Volumetric-Modulated Arc Therapy-Stereotactic Body Radiotherapy for Lung Cancer

PURPOSE: We investigated the performance of the simplified knowledge-based plans (KBPs) in stereotactic body radiotherapy (SBRT) with volumetric-modulated arc therapy (VMAT) for lung cancer. MATERIALS AND METHODS: For 50 cases who underwent SBRT, only three structures were registered into knowledge-based model: total lung, spinal cord, and planning target volume. We performed single auto-optimization on VMAT plans in two steps: 19 cases used for the model training (closed-loop validation) and 16 new cases outside of training set (open-loop validation) for TrueBeam (TB) and Halcyon (Hal) linacs. The dosimetric parameters were compared between clinical plans (CLPs) and KBPs: CLP(closed), KBP(closed)-TB and KBP(closed)-Hal in closed-loop validation, CLP(open), KBP(open)-TB and KBP(open)-Hal in open-loop validation. RESULTS: All organs at risk were comparable between CLPs and KBPs except for contralateral lung: V(5) of KBPs was approximately 3%–7% higher than that of CLPs. V(20) of total lung for KBPs showed comparable to CLPs; CLP(closed) vs. KBP(closed)-TB and CLP(closed) vs. KBP(closed)-Hal: 4.36% ± 2.87% vs. 3.54% ± 1.95% and 4.36 ± 2.87% vs. 3.54% ± 1.94% (P = 0.54 and 0.54); CLP(open) vs. KBP(open)-TB and CLP(open) vs. KBP(open)-Hal: 4.18% ± 1.57% vs. 3.55% ± 1.27% and 4.18% ± 1.57% vs. 3.67% ± 1.26% (P = 0.19 and 0.27). CI(95) of KBPs with both linacs was superior to that of the CLP in closed-loop validation: CLP(closed) vs. KBP(closed)-TB vs. KBP(closed)-Hal: 1.32% ± 0.12% vs. 1.18% ± 0.09% vs. 1.17% ± 0.06% (P < 0.01); and open-loop validation: CLP(open) vs. KBP(open)-TB vs. KBP(open)-Hal: 1.22% ± 0.09% vs. 1.14% ± 0.04% vs. 1.16% ± 0.05% (P ≤ 0.01). CONCLUSIONS: The simplified KBPs with limited number of structures and without planner intervention were clinically acceptable in the dosimetric parameters for lung VMAT-SBRT planning.