title: Local dose-effect relations for lung perfusion post stereotactic body radiotherapy.
abstract: OBJECTIVE
  To model the local dose-effect relation for lung perfusion reduction in lung cancer patients treated with stereotactic body radiotherapy (SBRT).
  
  
  METHODS
  Forty-two patients having upper-lobe peripheral tumours <5 cm treated with SBRT (3×18 Gy) underwent single-photon emission computed-tomography (SPECT) scans to measure the lung perfusion 2 weeks pre-SBRT, 4-months post-SBRT, and for 8 patients 15-months post-SBRT. The relation between the calculated relative local perfusion reduction and the normalised total dose (α/β=3 Gy) at 4-months post-SBRT was modeled by 3-parameter logistic model and 2-parameter linear-maximum model.
  
  
  RESULTS
  The relation between local dose and perfusion reduction at 4-months post-SBRT showed a maximum effect of 42.6% at doses >100 Gy and was best described by the logistic model with parameters (95% CI): M=42.6% (40.7-44.6), D50=28.7 Gy (26.3-31.1) and k=2.2 (1.8-2.5). A significant increase of this maximum effect to 65.2% was found at 15-months post-SBRT.
  
  
  CONCLUSIONS
  The relation between local dose and perfusion reduction in patients treated with SBRT can be modeled by a 3-parameter logistic model. This demonstrated relationship 4-months post-SBRT approaches a plateau for doses >100 Gy, where 90% of the maximum lung-perfusion reduction is observed at NTD=78 Gy. A further perfusion reduction compared to 4-months post-SBRT was observed fifteen months post-SBRT.
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute - Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands.
authors.forename: Alize E H
authors.initials: AE
authors.lastname: Scheenstra
authors.forename: Maddalena M G
authors.initials: MM
authors.lastname: Rossi
authors.forename: José S A
authors.initials: JS
authors.lastname: Belderbos
authors.forename: Eugène M F
authors.initials: EM
authors.lastname: Damen
authors.forename: Joos V
authors.initials: JV
authors.lastname: Lebesque
authors.forename: Jan-Jakob
authors.initials: JJ
authors.lastname: Sonke
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D016015:Logistic Models; D008168:Lung / Q000098:blood supply*; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D016634:Radiosurgery; D011880:Radiotherapy Planning, Computer-Assisted; D015899:Tomography, Emission-Computed, Single-Photon; D014057:Tomography, X-Ray Computed
keywords: Lung perfusion reduction; NTCP; SBRT; SPECT