Patterns and correlates of treatment failure in relation to isodose distribution in non-small cell lung cancer: An analysis of 1522 patients in the modern era.

BACKGROUND AND PURPOSE: To examine the relationship between radiation dose and tumor control in limited stage non-small cell lung cancer (NSCLC).

MATERIALS AND METHODS: We searched a database of 1552 patients who received radiation therapy for non-metastatic NSCLC between 2000 and 2016. The primary endpoint was freedom from in-field failure.

RESULTS: Increasing BED correlated with decreasing estimated gross tumor volume-planning target volume expansion, and on multivariable analysis increasing BED was associated with an increased chance of field-edge failures (hazard ratio [HR] 1.032, 95% confidence interval [CI] 1.004-1.062, P = 0.027). Increasing BED also correlated with improved freedom from in-field failure on multivariable analysis (HR 0.978, 95% CI 0.964-0.993, P = 0.003), with the dose-response curve showing a sigmoidal relationship between increasing BED and freedom from in-field failure.

CONCLUSION: In this large study of patients treated in the modern era with varying dose fractionation regimens, higher BED was associated with improved freedom from in-field failure, and that this relationship appeared to be consistent with the classically described sigmoid shape. We also found that increased BED was associated with higher field-edge failures, implying that margin size may need to be further studied in patients receiving ablative regimens of radiation.