• Radiother Oncol · Oct 2013

    Applicability of the linear-quadratic formalism for modeling local tumor control probability in high dose per fraction stereotactic body radiotherapy for early stage non-small cell lung cancer.

    • Matthias Guckenberger, Rainer Johannes Klement, Michael Allgäuer, Steffen Appold, Karin Dieckmann, Iris Ernst, Ute Ganswindt, Richard Holy, Ursula Nestle, Meinhard Nevinny-Stickel, Sabine Semrau, Florian Sterzing, Andrea Wittig, Nicolaus Andratschke, and Michael Flentje.
    • Department of Radiation Oncology, University of Würzburg, Germany. Electronic address: guckenberger_m@klinik.uni-wuerzburg.de.
    • Radiother Oncol. 2013 Oct 1; 109 (1): 13-20.

    Background And PurposeTo compare the linear-quadratic (LQ) and the LQ-L formalism (linear cell survival curve beyond a threshold dose dT) for modeling local tumor control probability (TCP) in stereotactic body radiotherapy (SBRT) for stage I non-small cell lung cancer (NSCLC).Materials And MethodsThis study is based on 395 patients from 13 German and Austrian centers treated with SBRT for stage I NSCLC. The median number of SBRT fractions was 3 (range 1-8) and median single fraction dose was 12.5 Gy (2.9-33 Gy); dose was prescribed to the median 65% PTV encompassing isodose (60-100%). Assuming an α/β-value of 10 Gy, we modeled TCP as a sigmoid-shaped function of the biologically effective dose (BED). Models were compared using maximum likelihood ratio tests as well as Bayes factors (BFs).ResultsThere was strong evidence for a dose-response relationship in the total patient cohort (BFs>20), which was lacking in single-fraction SBRT (BFs<3). Using the PTV encompassing dose or maximum (isocentric) dose, our data indicated a LQ-L transition dose (dT) at 11 Gy (68% CI 8-14 Gy) or 22 Gy (14-42 Gy), respectively. However, the fit of the LQ-L models was not significantly better than a fit without the dT parameter (p=0.07, BF=2.1 and p=0.86, BF=0.8, respectively). Generally, isocentric doses resulted in much better dose-response relationships than PTV encompassing doses (BFs>20).ConclusionOur data suggest accurate modeling of local tumor control in fractionated SBRT for stage I NSCLC with the traditional LQ formalism.Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

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