What would be the most appropriate α/β ratio in the setting of stereotactic body radiation therapy for early stage non-small cell lung cancer

Abstract

We hypothesize that the correlation between the radiation dose expressed as the biologically effective dose (BED) and the clinical endpoints will correlate better as the value of the α/β ratio is increased to >10 Gy, which theoretically minimizes the overestimation of the dose potency associated with the linear quadratic (LQ) formula in the setting of stereotactic body radiation therapy (SBRT) for early stage non-small cell lung cancer (NSCLC). A search was conducted in the PubMed electronic databases in August 2011. In the studies analyzed, increasing the α/β ratio is associated with an increase in the strength of the correlation between isocenter BED and local control, especially in the studies with median followup of ≥24 months, for which Spearman's correlation coefficients of 0.74-0.76 were achieved for α/β of 20 Gy, 30 Gy, and 50 Gy (P = 0.007-0.008). A trend toward statistical significance was observed for the correlation of isocenter BED and the 2-year overall survival when an α/β of 20 Gy was used approached statistical significance (P = 0.073). Our results suggest that an α/β > 10 Gy may be more appropriate for the prediction of dose response in the setting of lung SBRT.

Figure 1

The correlation between the fractional dose and the local control in studies which reported the outcome of dose fractionation schedules that delivered the total dose in 3 fractions. The size of the circle is proportional to the number of patients treated with a specific dose fractionation schedule in each study.

Figure 2

The correlation of the tumor BED at the isocenter calculated with a spectrum of α/β ratios (5, 8.2, 10, 20, 30, and 50 Gy) and the local control reported among all studies. Due to the use of different α/β ratios, the BED scale on the x-axis is different for each plot.

Figure 3

The correlation of the tumor BED at the isocenter calculated with a spectrum of α/β ratios (5, 8.2, 10, 20, 30, and 50 Gy) and the local control reported among studies with a median followup of ≥24 months. Due to the use of different α/β ratios, the BED scale on the x-axis is different for each plot.

Figure 4

The correlation of the tumor BED at the isocenter calculated with a spectrum of α/β ratios (5, 8.2, 10, 20, 30, and 50 Gy) and the 2-year overall survival reported in selected studies. Due to the use of different α/β ratios, the BED scale on the x-axis is different for each plot.