Local control dependence on consecutive vs. nonconsecutive fractionation in lung stereotactic body radiation therapy.

Background: Recent reports demonstrate impaired tumor re-oxygenation 24-48h after stereotactic body radiation therapy (SBRT), suggesting that non-consecutive treatment delivery may be advantageous. To test this hypothesis clinically, we compared local control in patients treated in consecutive daily fractions vs. nonconsecutive fractions.

Methods: We retrospectively reviewed 107 lung SBRT patients (117 tumors) treated for T1-T2N0 NSCLC with LINAC based SBRT (50 or 60Gy/5fractions). Patients were characterized as having been treated in consecutive daily fractions vs. in non-consecutive fractions. Local control, survival and toxicity end points (CTCAE V4.0) were compared. Propensity score matching and Cox regression analyses were performed in order to determine the effect of fractionation on local control.

Results: With a median follow up of 23.7months, 3-year local control was superior at 93.3% vs. 63.6% in the non-consecutive and consecutive group, respectively (p=0.001). Multivariate analysis and propensity score matching showed that consecutive fractionation was an independent predictor of local failure. Overall survival trended toward improvement in the non-consecutive group, but this was not statistically significant (p=0.188). Development of any grade 2 toxicity was not significantly different between the two groups (p=0.75).

Conclusion: Five-fraction SBRT delivered over non-consecutive days imparts superior LC and similar toxicity compared to consecutive fractionation. These results should be validated in independent datasets and in a prospective fashion.