title: Intensity-modulated radiotherapy might increase pneumonitis risk relative to three-dimensional conformal radiotherapy in patients receiving combined chemotherapy and radiotherapy: a modeling study of dose dumping.
abstract: OBJECTIVE
  To model the possible interaction between cytotoxic chemotherapy and the radiation dose distribution with respect to the risk of radiation pneumonitis.
  
  
  METHODS
  A total of 18 non-small-cell lung cancer patients previously treated with helical tomotherapy at the University of Wisconsin were selected for the present modeling study. Three treatment plans were considered: the delivered tomotherapy plans; a three-dimensional conformal radiotherapy (3D-CRT) plan; and a fixed-field intensity-modulated radiotherapy (IMRT) plan. The IMRT and 3D-CRT plans were generated specifically for the present study. The plans were optimized without adjusting for the chemotherapy effect. The effect of chemotherapy was modeled as an independent cell killing process by considering a uniform chemotherapy equivalent radiation dose added to all voxels of the organ at risk. The risk of radiation pneumonitis was estimated for all plans using the Lyman and the critical volume models.
  
  
  RESULTS
  For radiotherapy alone, the critical volume model predicts that the two IMRT plans are associated with a lower risk of radiation pneumonitis than the 3D-CRT plan. However, when the chemotherapy equivalent radiation dose exceeds a certain threshold, the radiation pneumonitis risk after IMRT is greater than after 3D-CRT. This threshold dose is in the range estimated from clinical chemoradiotherapy data sets.
  
  
  CONCLUSIONS
  Cytotoxic chemotherapy might affect the relative merit of competing radiotherapy plans. More work is needed to improve our understanding of the interaction between chemotherapy and the radiation dose distribution in clinical settings.
authors.affiliation: Department of Oncology, Vejle Sygehus, Vejle, Denmark. bentzen@humonc.wisc.edu
authors.forename: Ivan S
authors.initials: IS
authors.lastname: Vogelius
authors.forename: David C
authors.initials: DC
authors.lastname: Westerly
authors.forename: George M
authors.initials: GM
authors.lastname: Cannon
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Mackie
authors.forename: Minesh P
authors.initials: MP
authors.lastname: Mehta
authors.forename: Chikao
authors.initials: C
authors.lastname: Sugie
authors.forename: Søren M
authors.initials: SM
authors.lastname: Bentzen
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy* / Q000532:radiotherapy*; D003131:Combined Modality Therapy / Q000009:adverse effects / Q000379:methods; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000532:radiotherapy*; D008954:Models, Biological; D017564:Radiation Pneumonitis / Q000139:chemically induced / Q000209:etiology*; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal / Q000009:adverse effects; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects*