Predictive power of PTV volume for choosing manual or automatic planning in lung stereotactic body radiotherapy

Purpose: This study investigated the role of Planning Target Volume (PTV) in determining the suitability of manual and automatic Stereotactic Body Radiation Therapy (SBRT) planning for lung cancer patients. Methods: We retrospectively created manual and automatic lung SBRT plans for ninety-eight patients using the Pinnacle 16.2 Treatment Planning System (TPS). The superior plan, whether manual or automatic, was selected for each patient through a combined index. Receiver Operating Characteristic (ROC) analysis was used to assess the predictive potential of the PTV volume in determining the superior plan and to establish a cutoff value. Patients were then stratified into two groups based on this value, and dosimetric variances were evaluated. Results: The ROC analysis highlighted the PTV volume's proficiency in predicting the superior choice between manual and automatic lung SBRT plans (Area Under Curve (AUC): 0.918, p = 0.005). The delineated cutoff value was set at 22.675 cc. For PTV volumes below this threshold, automatic plans surpassed manual plans in the Conformity Index (CI), Gradient Index (GI), and lung doses. Conversely, for PTV volumes exceeding 22.675 cc, manual plans exhibited improved results in the Heterogeneity Index (HI), GI, and dosimetric metric of heart and lung. Conclusion: The PTV volume is a significant determinant in guiding the optimal selection between manual and automatic lung SBRT plans with the Pinnacle TPS. Automatic plans are recommended for patients with PTV volumes below 22.675 cc, and manual plans for those above this threshold.