title: Automated contouring error detection based on supervised geometric attribute distribution models for radiation therapy: a general strategy.
abstract: OBJECTIVE
  One of the most critical steps in radiation therapy treatment is accurate tumor and critical organ-at-risk (OAR) contouring. Both manual and automated contouring processes are prone to errors and to a large degree of inter- and intraobserver variability. These are often due to the limitations of imaging techniques in visualizing human anatomy as well as to inherent anatomical variability among individuals. Physicians/physicists have to reverify all the radiation therapy contours of every patient before using them for treatment planning, which is tedious, laborious, and still not an error-free process. In this study, the authors developed a general strategy based on novel geometric attribute distribution (GAD) models to automatically detect radiation therapy OAR contouring errors and facilitate the current clinical workflow.
  
  
  METHODS
  Considering the radiation therapy structures' geometric attributes (centroid, volume, and shape), the spatial relationship of neighboring structures, as well as anatomical similarity of individual contours among patients, the authors established GAD models to characterize the interstructural centroid and volume variations, and the intrastructural shape variations of each individual structure. The GAD models are scalable and deformable, and constrained by their respective principal attribute variations calculated from training sets with verified OAR contours. A new iterative weighted GAD model-fitting algorithm was developed for contouring error detection. Receiver operating characteristic (ROC) analysis was employed in a unique way to optimize the model parameters to satisfy clinical requirements. A total of forty-four head-and-neck patient cases, each of which includes nine critical OAR contours, were utilized to demonstrate the proposed strategy. Twenty-nine out of these forty-four patient cases were utilized to train the inter- and intrastructural GAD models. These training data and the remaining fifteen testing data sets were separately employed to test the effectiveness of the proposed contouring error detection strategy.
  
  
  RESULTS
  An evaluation tool was implemented to illustrate how the proposed strategy automatically detects the radiation therapy contouring errors for a given patient and provides 3D graphical visualization of error detection results as well. The contouring error detection results were achieved with an average sensitivity of 0.954/0.906 and an average specificity of 0.901/0.909 on the centroid/volume related contouring errors of all the tested samples. As for the detection results on structural shape related contouring errors, an average sensitivity of 0.816 and an average specificity of 0.94 on all the tested samples were obtained. The promising results indicated the feasibility of the proposed strategy for the detection of contouring errors with low false detection rate.
  
  
  CONCLUSIONS
  The proposed strategy can reliably identify contouring errors based upon inter- and intrastructural constraints derived from clinically approved contours. It holds great potential for improving the radiation therapy workflow. ROC and box plot analyses allow for analytically tuning of the system parameters to satisfy clinical requirements. Future work will focus on the improvement of strategy reliability by utilizing more training sets and additional geometric attribute constraints.
authors: Department of Radiation Oncology, Washington University, St. Louis, Missouri 63110.
authors: Hsin-Chen
authors: HC
authors: Chen
authors: Department of Radiation Oncology, Washington University, St. Louis, Missouri 63110.
authors: Jun
authors: J
authors: Tan
authors: Department of Radiation Oncology, Washington University, St. Louis, Missouri 63110.
authors: Steven
authors: S
authors: Dolly
authors: Department of Radiation Oncology, Washington University, St. Louis, Missouri 63110.
authors: James
authors: J
authors: Kavanaugh
authors: Department of Biomedical Engineering, Washington University, St. Louis, Missouri 63110.
authors: Mark A
authors: MA
authors: Anastasio
authors: Department of Radiation Oncology, University of California Los Angeles, Los Angeles, California 90095.
authors: Daniel A
authors: DA
authors: Low
authors: Department of Radiation Oncology, Washington University, St. Louis, Missouri 63110.
authors: H Harold
authors: HH
authors: Li
authors: Department of Radiation Oncology, Washington University, St. Louis, Missouri 63110.
authors: Michael
authors: M
authors: Altman
authors: Department of Radiation Oncology, Washington University, St. Louis, Missouri 63110.
authors: Hiram
authors: H
authors: Gay
authors: Department of Radiation Oncology, Washington University, St. Louis, Missouri 63110.
authors: Wade L
authors: WL
authors: Thorstad
authors: Department of Radiation Oncology, Washington University, St. Louis, Missouri 63110.
authors: Sasa
authors: S
authors: Mutic
authors: Department of Radiation Oncology, Washington University, St. Louis, Missouri 63110.
authors: Hua
authors: H
authors: Li
mesh_terms: D001331:Automation; D006258:Head and Neck Neoplasms / Q000532:radiotherapy; D006801:Humans; D008962:Models, Theoretical; D058958:Organs at Risk / Q000528:radiation effects; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D011881:Radiotherapy, Computer-Assisted / Q000009:adverse effects