• Alize E H Scheenstra, Maddalena M G Rossi, José S A Belderbos, Eugène M F Damen, Joos V Lebesque, and Jan-Jakob Sonke.
• Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
• Int. J. Radiat. Oncol. Biol. Phys. 2014 Jan 1; 88 (1): 224-8.

PurposeTo 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 And MaterialsThe 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.ResultsThe 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).ConclusionsAn 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).Copyright © 2014 Elsevier Inc. All rights reserved.

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