Knowledge-Based Statistical Inference Method for Plan Quality Quantification

The aim of the study is to develop a geometrically adaptive and statistically robust plan quality inference method. A knowledge-based plan quality inference method is proposed in this study. It references to similar plans in the history database for patient-specific plan quality evaluation. Similar plans are retrieved using a novel plan similarity metric, and dosimetric statistical inferences are obtained from the selected similar plans. Two plan quality metrics—dosimetric result probability (DRP) and dose deviation index (DDI)—are proposed to quantify plan quality amongst prior similar plans. 927 clinical approved head-and-neck treatment plans with two planning targets were exported and used as the historical database. Eight organs-at-risk (OARs), including brainstem, spinal cord, larynx, mandible, pharynx, oral cavity, left parotid and right parotid were analyzed in this study. Statistical analysis is performed to validate the similarity of the selected reference plans. 12 sub-optimal plans identified by DRP were re-planned to validate the capability of the proposed methods in identifying inferior plans, To demonstrate the potential of our proposed method as a plan quality data analytics tool, a population-wise analysis was conducted on all retrieved plans sorted every two years. A ready-to-use stand-along application was also developed to streamline the evaluation process.

After replanning, left and right parotid median dose are reduced by 31.7\% and 18.2\% respectively. 83\% of these cases would not be identified as suboptimal without the proposed similarity plan selection. The population plan quality analysis reveals that the average parotid sparing has increased by 21.7\% from 2005 to 2018. Notably, the increasing dose sparing over time in retrospective plan quality analysis is strongly correlated with the increasing dose prescription ratios to the two planning targets, revealing the collective trend in planning conventions.

The proposed similar plan retrieval and analysis methodology has been proven to be predictive of the current plan quality. Therefore, the proposed workflow can potentially be applied in the clinics as a real-time plan quality assurance tool. The proposed metrics can also serve the purpose of plan quality analytics in finding connections and historical trends in the clinical treatment planning workflow.