title: Analysis of radiation pneumonitis risk using a generalized Lyman model.
abstract: OBJECTIVE
  To introduce a version of the Lyman normal-tissue complication probability (NTCP) model adapted to incorporate censored time-to-toxicity data and clinical risk factors and to apply the generalized model to analysis of radiation pneumonitis (RP) risk.
  
  
  METHODS
  Medical records and radiation treatment plans were reviewed retrospectively for 576 patients with non-small cell lung cancer treated with radiotherapy. The time to severe (Grade >/=3) RP was computed, with event times censored at last follow-up for patients not experiencing this endpoint. The censored time-to-toxicity data were analyzed using the standard and generalized Lyman models with patient smoking status taken into account.
  
  
  RESULTS
  The generalized Lyman model with patient smoking status taken into account produced NTCP estimates up to 27 percentage points different from the model based on dose-volume factors alone. The generalized model also predicted that 8% of the expected cases of severe RP were unobserved because of censoring. The estimated volume parameter for lung was not significantly different from n = 1, corresponding to mean lung dose.
  
  
  CONCLUSIONS
  NTCP models historically have been based solely on dose-volume effects and binary (yes/no) toxicity data. Our results demonstrate that inclusion of nondosimetric risk factors and censored time-to-event data can markedly affect outcome predictions made using NTCP models.
authors.affiliation: Department of Bioinformatics and Computational Biology, The University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030, USA. sltucker@mdanderson.org
authors.forename: Susan L
authors.initials: SL
authors.lastname: Tucker
authors.forename: H Helen
authors.initials: HH
authors.lastname: Liu
authors.forename: Zhongxing
authors.initials: Z
authors.lastname: Liao
authors.forename: Xiong
authors.initials: X
authors.lastname: Wei
authors.forename: Shulian
authors.initials: S
authors.lastname: Wang
authors.forename: Hekun
authors.initials: H
authors.lastname: Jin
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Komaki
authors.forename: Mary K
authors.initials: MK
authors.lastname: Martel
authors.forename: Radhe
authors.initials: R
authors.lastname: Mohan
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000401:mortality / Q000532:radiotherapy*; D006801:Humans; D008168:Lung / Q000528:radiation effects; D008175:Lung Neoplasms / Q000401:mortality / Q000532:radiotherapy*; D015233:Models, Statistical; D011336:Probability; D017564:Radiation Pneumonitis / Q000209:etiology* / Q000401:mortality; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal; D012189:Retrospective Studies; D012907:Smoking / Q000009:adverse effects; D013997:Time Factors
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