title: Predicting lung radiotherapy-induced pneumonitis using a model combining parametric Lyman probit with nonparametric decision trees.
abstract: OBJECTIVE
  To develop and test a model to predict for lung radiation-induced Grade 2+ pneumonitis.
  
  
  METHODS
  The model was built from a database of 234 lung cancer patients treated with radiotherapy (RT), of whom 43 were diagnosed with pneumonitis. The model augmented the predictive capability of the parametric dose-based Lyman normal tissue complication probability (LNTCP) metric by combining it with weighted nonparametric decision trees that use dose and nondose inputs. The decision trees were sequentially added to the model using a "boosting" process that enhances the accuracy of prediction. The model's predictive capability was estimated by 10-fold cross-validation. To facilitate dissemination, the cross-validation result was used to extract a simplified approximation to the complicated model architecture created by boosting. Application of the simplified model is demonstrated in two example cases.
  
  
  RESULTS
  The area under the model receiver operating characteristics curve for cross-validation was 0.72, a significant improvement over the LNTCP area of 0.63 (p = 0.005). The simplified model used the following variables to output a measure of injury: LNTCP, gender, histologic type, chemotherapy schedule, and treatment schedule. For a given patient RT plan, injury prediction was highest for the combination of pre-RT chemotherapy, once-daily treatment, female gender and lowest for the combination of no pre-RT chemotherapy and nonsquamous cell histologic type. Application of the simplified model to the example cases revealed that injury prediction for a given treatment plan can range from very low to very high, depending on the settings of the nondose variables.
  
  
  CONCLUSIONS
  Radiation pneumonitis prediction was significantly enhanced by decision trees that added the influence of nondose factors to the LNTCP formulation.
authors.affiliation: Department of Radiation Oncology, Duke University Medical Center, Durham, NC 27710, USA. shiva.das@duke.edu
authors.forename: Shiva K
authors.initials: SK
authors.lastname: Das
authors.forename: Sumin
authors.initials: S
authors.lastname: Zhou
authors.forename: Junan
authors.initials: J
authors.lastname: Zhang
authors.forename: Fang-Fang
authors.initials: FF
authors.lastname: Yin
authors.forename: Mark W
authors.initials: MW
authors.lastname: Dewhirst
authors.forename: Lawrence B
authors.initials: LB
authors.lastname: Marks
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003663:Decision Trees; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D012372:ROC Curve; D017564:Radiation Pneumonitis / Q000209:etiology*; D011859:Radiography; D015203:Reproducibility of Results