title: Predicting changes in dose distribution to tumor and normal tissue when correcting for heterogeneity in radiotherapy for lung cancer.
abstract: OBJECTIVE
  The purposes of this study were to examine dose alterations to gross tumor volume (GTV) and lung using heterogeneity corrections and to predict the magnitude of these changes.
  
  
  METHODS
  Three separate conformal plans were generated for 37 patients with lung cancer: plan 1 corrected for heterogeneity, plan 2 did not correct for heterogeneity, and plan 3 used identical beams and monitor units from plan 2 but with heterogeneous calculations. Plans 1 and 2 were normalized to the 95% isodose line. Mean dose (MeanDGTV), maximum dose (MaxDGTV), and minimum dose (MinDGTV) to GTV and V20 were compared between plans 1 and 3. For each patient, the amount of lung in all beam paths of plan 3 was quantified by a density correction factor and correlated with the percent change.
  
  
  RESULTS
  The median percent change in MeanDGTV, MaxDGTV, and MinDGTV between plan 3 and plan 1 was -4.7% (-0.1% to -19.1%, P < 0.0001), -5.59% (0.16% to -31.86%, P < 0.0001), and -4.88% (2.90% to -24.88%, P < 0.0001), respectively. The median V20 difference was -1% (1% to -8%). The density correction factor correlated with larger differences in MeanDGTV on univariate analysis.
  
  
  CONCLUSIONS
  Heterogeneity correction lowers the dose to GTV by 5%. This difference can be correlated with the density correction factor.
authors.affiliation: Department of Radiation Oncology, University of Florida College of Medicine, Gainesville, Florida 32610-0385, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Chang
authors.forename: Chihray
authors.initials: C
authors.lastname: Liu
authors.forename: James F
authors.initials: JF
authors.lastname: Dempsey
authors.forename: Jatinder R
authors.initials: JR
authors.lastname: Palta
authors.forename: Jill
authors.initials: J
authors.lastname: Kopea
authors.forename: Debbie
authors.initials: D
authors.lastname: Louis
authors.forename: Christopher
authors.initials: C
authors.lastname: Morris
authors.forename: Rahul
authors.initials: R
authors.lastname: Chopra
authors.forename: Kenneth R
authors.initials: KR
authors.lastname: Olivier
mesh_terms: D000704:Analysis of Variance; D002289:Carcinoma, Non-Small-Cell Lung / Q000473:pathology / Q000532:radiotherapy*; D018288:Carcinoma, Small Cell / Q000473:pathology / Q000532:radiotherapy*; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D009367:Neoplasm Staging; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D013909:Thorax / Q000528:radiation effects*; D014057:Tomography, X-Ray Computed