Local Control Dependence on Consecutive Versus Nonconsecutive Fractionation in Lung SBRT: A Propensity Score Matched Analysis

The Effect of Biologically Effective Dose and Radiation Treatment Schedule on Overall Survival in Stage I Non-Small Cell Lung Cancer Patients Treated With Stereotactic Body Radiation Therapy

PURPOSE

To determine the effect of biologically effective dose (BED₁₀) and radiation treatment schedule on overall survival (OS) in patients with early-stage non-small cell lung cancer (NSCLC) undergoing stereotactic body radiation therapy (SBRT).

METHODS AND MATERIALS

Using data from 65 treatment centers in the United States, we retrospectively reviewed the records of T1-2 N0 NSCLC patients undergoing SBRT alone from 2006 to 2014. Biologically relevant covariates, including dose per fraction, number of fractions, and time between fractions, were used to quantify BED₁₀ and radiation treatment schedule. The linear-quadratic equation was used to calculate BED₁₀ and to generate a dichotomous dose variable of <105 Gy versus ≥105 Gy BED₁₀. The primary outcome was OS. We used the Kaplan-Meier method, the log-rank test, and Cox proportional hazards regression with propensity score matching to determine whether prescription BED₁₀ was associated with OS.

RESULTS

We identified 747 patients who met inclusion criteria. The median BED₁₀ was 132 Gy, and 59 (7.7%) had consecutive-day fractions. Median follow-up was 41 months, and 452 patients (60.5%) had died by the conclusion of the study. The 581 patients receiving ≥105 Gy BED₁₀ had a median survival of 28 months, whereas the 166 patients receiving <105 Gy BED₁₀ had a median survival of 22 months (log-rank, P=.01). Radiation treatment schedule was not a significant predictor of OS on univariable analysis. After adjusting for T stage, sex, tumor histology, and Eastern Cooperative Oncology Group performance status, BED₁₀ ≥105 Gy versus <105 Gy remained significantly associated with improved OS (hazard ratio 0.78, 95% confidence interval 0.62-0.98, P=.03). Propensity score matching on imbalanced variables within high- and low-dose cohorts confirmed a survival benefit with higher prescription dose.

CONCLUSIONS

We found that dose escalation to 105 Gy BED₁₀ and beyond may improve survival in NSCLC patients treated with SBRT.