title: Radiation dose response of normal lung assessed by Cone Beam CT - a potential tool for biologically adaptive radiation therapy.
abstract: BACKGROUND
  Density changes of healthy lung tissue during radiotherapy as observed by Cone Beam CT (CBCT) might be an early indicator of patient specific lung toxicity. This study investigates the time course of CBCT density changes and tests for a possible correlation with locally delivered dose.
  
  
  METHODS
  A total of 665 CBCTs in 65 lung cancer patients treated with IMRT/VMAT to 60 or 66 Gy in 2 Gy fractions were analyzed. For each patient, CBCT lung density changes during the treatment course were related to the locally delivered dose.
  
  
  RESULTS
  A dose response is observed for the patient population at the end of the treatment course. However, the observed dose response is highly variable among patients. Density changes at 10th and 20th fraction are clearly correlated to those observed at the end of the treatment course.
  
  
  CONCLUSIONS
  CBCT density changes in healthy lung tissue during radiotherapy correlate with the locally delivered dose and can be detected relatively early during the treatment. If these density changes are correlated to subsequent clinical toxicity this assay could form the basis for biological adaptive radiotherapy.
authors: Institute of Clinical Research, University of Southern Denmark, Odense, Denmark. anders.bertelsen@ouh.regionsyddanmark.dk
authors: Anders
authors: A
authors: Bertelsen
authors: Tine
authors: T
authors: Schytte
authors: Søren M
authors: SM
authors: Bentzen
authors: Olfred
authors: O
authors: Hansen
authors: Morten
authors: M
authors: Nielsen
authors: Carsten
authors: C
authors: Brink
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D054893:Cone-Beam Computed Tomography; D019583:Dose Fractionation, Radiation; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging* / Q000528:radiation effects*; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012189:Retrospective Studies; D018709:Statistics, Nonparametric; D016896:Treatment Outcome