title: Regional variability in radiation-induced lung damage can be predicted by baseline CT numbers.
abstract: Lung volumes are functionally heterogeneous but typically considered uniformly during radiotherapy planning. The present study aims to predict regional differences in radiation-induced lung damage based on pre-treatment CT information.
  
  
  
  For 42 lung cancer patients (including 15 from an external validation set), two 200cc lung subvolumes (low-density (LD) and high-density (HD)) were auto-segmented in the ipsilateral lung of the planning CT0.After non-rigid registration of 3month follow-up CT scans, sigmoidal dose-density change (ΔHU=HU3M-HU0) response curves were determined for all subvolumes. Predictive factors for the sigmoidal response parameters D50and saturation level ΔHUmaxwere analyzed.
  
  
  
  The baseline density difference between LD (mostly in the upper lobe) and HD (mostly in the lower lobe) was on average 102HU. The saturation level ΔHUmax,LDwas significantly smaller than ΔHUmax,HD(p=0.03). Expressed as mass density increase relative to the baseline density, saturation levels were 20.7% on average irrespective of baseline density, and they could be predicted in LD and HD subvolumes (AUC=0.70-0.78). Intra-lung differences in D50were significantly smaller than inter-patient differences.
  
  
  
  Limited amount of damage was observed in LD subvolumes, while the relative density increase of all subvolumes was well predictable. This could allow dose redistribution preferentially targeting low-density lung regions.
authors.affiliation: KU Leuven - University of Leuven, Department of Oncology, Experimental Radiation Oncology, Belgium; KU Leuven Medical Imaging Research Center, Belgium. Electronic address: gilles.defraene@uzleuven.be.
authors.forename: Gilles
authors.initials: G
authors.lastname: Defraene
authors.affiliation: Department of Radiation Oncology (MAASTRO), GROW - School for Oncology and Developmental Biology, Maastricht University Medical Centre, The Netherlands.
authors.forename: Wouter
authors.initials: W
authors.lastname: van Elmpt
authors.affiliation: University Hospitals Leuven, Department of Radiation Oncology, Belgium.
authors.forename: Wouter
authors.initials: W
authors.lastname: Crijns
authors.affiliation: KU Leuven - University of Leuven, Department of Oncology, Experimental Radiation Oncology, Belgium; Department of Radiation Oncology (MAASTRO), GROW - School for Oncology and Developmental Biology, Maastricht University Medical Centre, The Netherlands.
authors.forename: Dirk
authors.initials: D
authors.lastname: De Ruysscher
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008168:Lung / Q000528:radiation effects*; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D011832:Radiation Injuries / Q000453:epidemiology*; D011879:Radiotherapy Dosage; D014057:Tomography, X-Ray Computed / Q000379:methods*; D047368:Tumor Burden; D055815:Young Adult
keywords: CT; Density change; Lung cancer; Radiation-induced lung damage; Radiosensitivity; Regional heterogeneity