title: CT characteristics allow identification of patient-specific susceptibility for radiation-induced lung damage.
abstract: OBJECTIVE
  There is a huge difference in radiosensitivity of lungs between patients. The present study aims to identify and quantify patient-specific radiosensitivity based on a single pre-treatment CT scan.
  
  
  METHODS
  130 lung cancer patients were studied: 60 stereotactic ablative radiotherapy (SABR) treatments and 70 conventional treatments (20 and 30 patients from external datasets, respectively). A 3month-follow-up scan (CT3M) was non-rigidly registered to the planning CT scan (CT0). Changes in Hounsfield Units (ΔHU=HU3M-HU0) inside lung subvolumes were analyzed per dose bin of 5Gy. ΔHU was modeled as a function of local dose using linear and sigmoidal fits. Sigmoidal fit parameters ΔHUmax (saturation level) and D50 (dose corresponding to 50% of ΔHUmax) were collected for all patients.
  
  
  RESULTS
  Sigmoidal fits outperformed linear fits in the SABR groups for the majority of patients. Sigmoidal dose-responses were also observed in both conventional groups but to a lesser extent. Distributions of D50 and ΔHUmax showed a large variation between patients in all datasets. Higher baseline lung density (p<0.001) was prognostic for higher ΔHUmax in one SABR group. No prognostic factors were found for D50.
  
  
  CONCLUSIONS
  Baseline CT characteristics are prognostic for radiation-induced lung damage susceptibility.
authors.affiliation: KU Leuven - University of Leuven, Department of Oncology, Experimental Radiation Oncology, B-3000 Leuven, 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: KU Leuven - University of Leuven, Department of Oncology, Experimental Radiation Oncology, B-3000 Leuven, Belgium; University Hospitals Leuven, Department of Radiation Oncology, B-3000 Leuven, Belgium; KU Leuven Medical Imaging Research Center, B-3000 Leuven, Belgium.
authors.forename: Wouter
authors.initials: W
authors.lastname: Crijns
authors.affiliation: KU Leuven Medical Imaging Research Center, B-3000 Leuven, Belgium; KU Leuven, ESAT/PSI - UZ Leuven, MIRC - iMinds, Medical IT Dept, Belgium.
authors.forename: Pieter
authors.initials: P
authors.lastname: Slagmolen
authors.affiliation: KU Leuven - University of Leuven, Department of Oncology, Experimental Radiation Oncology, B-3000 Leuven, Belgium; University Hospitals Leuven, Department of Radiation Oncology, B-3000 Leuven, Belgium.
authors.forename: Dirk
authors.initials: D
authors.lastname: De Ruysscher
mesh_terms: D004307:Dose-Response Relationship, Radiation; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy / Q000601:surgery; D015233:Models, Statistical; D011379:Prognosis; D011832:Radiation Injuries / Q000000981:diagnostic imaging* / Q000209:etiology; D011836:Radiation Tolerance; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods
keywords: CT; Density change; Lung cancer; Radiation-induced lung damage; Radiosensitivity; Stereotactic ablative radiotherapy