title: Alpha/beta ratio for normal lung tissue as estimated from lung cancer patients treated with stereotactic body and conventionally fractionated radiation therapy.
abstract: OBJECTIVE
  To estimate the α/β ratio for which the dose-dependent lung perfusion reductions for stereotactic body radiation therapy (SBRT) and conventionally fractionated radiation therapy (CFRT) are biologically equivalent.
  
  
  METHODS
  The relations between local dose and perfusion reduction 4 months after treatment in lung cancer patients treated with SBRT and CFRT were scaled according to the linear-quadratic model using α/β ratios from 0 Gy to ∞ Gy. To test for which α/β ratio both treatments have equal biological effect, a 5-parameter logistic model was optimized for both dose-effect relationships simultaneously. Beside the α/β ratio, the other 4 parameters were d50, the steepness parameter k, and 2 parameters (MSBRT and MCFRT) representing the maximal perfusion reduction at high doses for SBRT and CFRT, respectively.
  
  
  RESULTS
  The optimal fitted model resulted in an α/β ratio of 1.3 Gy (0.5-2.1 Gy), MSBRT=42.6% (40.4%-44.9%), MCFRT=66.9% (61.6%-72.1%), d50=35.4 Gy (31.5-9.2 Gy), and k=2.0 (1.7-2.3).
  
  
  CONCLUSIONS
  An equal reduction of lung perfusion in lung cancer was observed in SBRT and CFRT if local doses were converted by the linear-quadratic model with an α/β ratio equal to 1.3 Gy (0.5-2.1 Gy).
authors: Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors: Alize E H
authors: AE
authors: Scheenstra
authors: Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors: Maddalena M G
authors: MM
authors: Rossi
authors: Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors: José S A
authors: JS
authors: Belderbos
authors: Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors: Eugène M F
authors: EM
authors: Damen
authors: Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors: Joos V
authors: JV
authors: Lebesque
authors: Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands. Electronic address: j.sonke@nki.nl.
authors: Jan-Jakob
authors: JJ
authors: Sonke
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002289:Carcinoma, Non-Small-Cell Lung / Q000503:physiopathology / Q000532:radiotherapy* / Q000601:surgery*; D002470:Cell Survival / Q000528:radiation effects; D019583:Dose Fractionation, Radiation; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D016014:Linear Models; D008168:Lung / Q000503:physiopathology / Q000528:radiation effects*; D008175:Lung Neoplasms / Q000503:physiopathology / Q000532:radiotherapy* / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D016634:Radiosurgery; D012062:Relative Biological Effectiveness; D012189:Retrospective Studies