Abstract

PURPOSE: Numerous dose and fractionation schedules have been used to treat medically inoperable stage I Non-small cell lung cancer (NSCLC) with stereotactic body radiation therapy (SBRT) or stereotactic ablative radiotherapy (SABR). We evaluated published experiences with SBRT to determine local control (LC) rates as a function of SBRT dose.METHODS: One hundred sixty published articles reporting LC rates following SBRT for stage I NSCLC were identified. Quality of the series was assessed by evaluating the number of patients in the study, homogeneity of the dose regimen, length of follow-up time, and reporting of LC. Clinical data including 1, 2, 3, and 5 year tumor control probabilities for T1, T2, and combined T1 and T2 stage as a function of the biological effective dose were fitted to the linear quadratic (LQ), Universal survival curve (USC), and regrowth models.RESULTS: Forty-six studies met inclusion criteria. As measured by the goodness of fit chi2/ndf, with ndf as the number of degrees of freedom, none of the models were ideal fits for the data. Of the three models, the regrowth model provides the best fit to the clinical data. For the regrowth model, the fitting yielded an alpha/beta ratio of approximately 25 Gy for T1 tumors, 19 Gy for T2 tumors, and 21 Gy for T1 and T2 combined. In order to achieve the maximal LC rate, the predicted physical dose schemes when prescribed at the periphery of the planning target volume (PTV) are 43 +/- 1 Gy in 3 fractions, 47 +/- 1 Gy in 4 fractions, and 50 +/- 1 Gy in 5 fractions for combined T1 and T2 tumors.CONCLUSION: Early stage NSCLC is radioresponsive when treated with SBRT/SABR. A steep dose-response relationship exists with high rates of durable LC when physical doses of 43-50 Gy are delivered in 3-5 fractions.

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