Estimation of the α/β ratio of non-small cell lung cancer treated with stereotactic body radiotherapy.
Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology
BACKGROUND: High-dose hypofractionated radiotherapy should theoretically result in a deviation from the typical linear-quadratic shape of the cell survival curve beyond a certain threshold dose, yet no evidence for this hypothesis has so far been found in clinical data of stereotactic body radiotherapy treatment (SBRT) for early-stage non-small cell lung cancer (NSCLC). A pragmatic explanation is a larger α/β ratio than the conventionally assumed 10 Gy. We here attempted an estimation of the α/β ratio for NSCLC treated with SBRT using individual patient data.
MATERIALS AND METHODS: We combined two large retrospective datasets, yielding 1294 SBRTs (≤10 fractions) of early stage NSCLC. Cox proportional hazards regression, a logistic tumor control probability model and a biologically motivated Bayesian cure rate model were used to estimate the α/β ratio based on the observed number of local recurrences and accounting for tumor size.
RESULTS: A total of 109 local progressions were observed after a median of 17.7 months (range 0.6-76.3 months). Cox regression, logistic regression of 3 year tumor control probability and the cure rate model yielded best-fit estimates of α/β = 12.8 Gy, 14.9 Gy and 12-16 Gy (depending on the prior for α/β), respectively, although with large uncertainties that did not rule out the conventional α/β = 10 Gy.
CONCLUSIONS: Clinicians can continue to use the simple LQ formalism to compare different SBRT treatment schedules for NSCLC. While α/β = 10 Gy is not ruled out by our data, larger values in the range 12-16 Gy are more probable, consistent with recent meta-regression analyses.
Klement RJ, Sonke JJ, Allgäuer M, Andratschke N, Appold S, Belderbos J, Belka C, Dieckmann K, Eich HT, Flentje M, Grills I, Eble M, Hope A, Grosu AL, Semrau S, Sweeney RA, Hörner-Rieber J, Werner-Wasik M, Engenhart-Cabillic R, Ye H, Guckenberger M. Estimation of the α/β ratio of non-small cell lung cancer treated with stereotactic body radiotherapy. Radiother Oncol. 2020 Jan;142:210-216. doi: 10.1016/j.radonc.2019.07.008. Epub 2019 Aug 17. PMID: 31431371.