Database Plan Quality Impact on Knowledge-based Radiation Therapy Treatment Planning of Prostate Cancer

Purpose: Knowledge-based planning (KBP) leverages plan data from a database of previously treated patients to inform the plan design of a new patient. This work investigated bladder and rectum dose-volume prediction improvements in a common KBP method using a Pareto plan database in VMAT planning for prostate cancer. Methods: We formed an anonymized retrospective patient database of 124 VMAT plans for prostate cancer treated at our institution. From these patient data, two plan databases were compiled. The clinical plan database (CPD) contained planning data from each patient’s clinical plan, which were manually optimized by various planners. The multi-criteria optimization database (MCOD) contained Pareto plan data from plans created using a standardized MCO protocol. Overlap volume histograms, incorporating fractional OAR volumes only within the treatment fields, were computed for each patient and used to match new patient anatomy to similar database patients. For each database patient, CPD and MCOD KBP predictions were generated for D_10, D_30, D_50, D_65, and D_80 of the bladder and rectum in a leave-one-out manner. Prediction achievability was verified through a re-planning study on a subset of 31 randomly selected database patients using the lowest KBP predictions, regardless of plan database origin, as planning goals. Results: MCOD model predictions were significantly lower (p \u3c 0.001) than CPD model predictions for all five bladder dose-volumes and rectum D_50 (p = 0.004) and D_65 (p \u3c 0.001), while CPD model predictions for rectum D_10 (p = 0.005) and D_30 (p \u3c 0.001) were significantly less than MCOD model predictions. KBP model predictions were statistically equivalent to re-planned values for all predicted dose-volumes, excluding D_10 of bladder (p = 0.03) and rectum (p = 0.04). Compared to clinical plans, re-plans showed significant average reductions in D_mean for bladder (7.8 Gy; p \u3c 0.001) and rectum (9.4 Gy; p \u3c 0.001), while maintaining statistically similar PTV, femoral head, and penile bulb dose. Conclusion: KBP dose-volume predictions derived from Pareto plans were lower overall than those resulting from manually optimized clinical plans. A re-planning study showed the KBP dose-volume predictions were achievable and led to significant reductions in bladder and rectum dose

Towards Optimizing Quality Assurance Outcomes of Knowledge-Based Radiation Therapy Treatment Plans Using Machine Learning

Knowledge-based planning (KBP) techniques have been shown to provide improvements in plan quality, consistency, and efficiency for advanced radiation therapies such as volumetric modulated arc therapy (VMAT). While the potential clinical benefits of KBP methods are generally well known, comparatively less is understood regarding the impact of using these systems on resulting plan complexity and pre-treatment quality assurance (QA) measurements, especially for in-house KBP systems. Therefore, the overarching purpose of this work was to assess QA implications with using an in-house KBP system and explore data-driven methods for mitigating increased plan complexity and QA error rates without compromising dosimetric plan quality. Specifically, this study evaluated differences in dose, complexity, and QA outcomes between reference clinical plans and plans designed with a previously established in-house KBP system. Further, a machine learning model – trained and tested using a database of 500 previous VMAT treatment plans and QA measurements – was developed to predict VMAT QA measurements based on selected mechanical features of the plan. This model was deployed as a feedback mechanism within a heuristic optimization algorithm designed to modify plan parameters (identified by the machine learning model as important for accurately predicting QA outcomes) towards improving the predicted delivery accuracy of the plan. While KBP plans achieved average reductions of 6.4 Gy (p \u3c 0.001) and 8.2 Gy (p \u3c 0.001) in mean bladder and rectum dose compared to reference clinical plans across thirty-one prostate patients, significant (p \u3c 0.05) increases in both complexity and QA measurement errors were observed. A support vector machine (SVM) was developed – using a database of 500 previous VMAT plans – to predict gamma passing rates (GPRs; 3%/3mm percent dose-difference/distance-to-agreement with local normalization) based on selected complexity features. A QA-based optimization algorithm was devised by utilizing the SVM model to iteratively modify mechanical treatment features most commonly associated with suboptimal GPRs. The feasibility was evaluated on 13 prostate VMAT plans designed with an in-house KBP method. Using a maximum random leaf gap displacement setting of 3 mm, predicted GPRs increased by an average of 1.14 ± 1.25% (p = 0.006) with minimal differences in dose and radiobiological metrics