Metabolic tumor volume predicts overall survival and local control in patients with stage III non-small cell lung cancer treated in ACRIN 6668/RTOG 0235.

PURPOSE: To determine whether higher pre-treatment metabolic tumor volume (tMTV-pre) is associated with worse overall survival (OS) in patients with inoperable NSCLC treated with definitive chemoradiation (CRT).

METHODS: This is a secondary analysis of the American College of Radiology Imaging Network (ACRIN) 6668/Radiation Therapy Oncology Group 0235 trial. Pre-treatment PET scans were performed on ACRIN-qualified scanners. Computer-aided MTV measurement was performed using RT_Image. Kaplan-Meier curves and Cox proportional hazards regression models were used to assess the association between tMTV and OS.

RESULTS: Of the 250 patients enrolled on the study, 230 were evaluable for tMTV-pre. Patients with MTV-pre >32 mL (median value) vs. ≤32 mL had worse median OS (14.8 vs. 29.7 months, p < 0.001). As a continuous variable, higher tMTV-pre (per 10-mL increase) remained associated with worse OS (HR = 1.03, p < 0.001) after controlling for other variables. A significant interaction between radiation dose and tMTV-pre occurred for OS (p = 0.002), demonstrating that the negative prognostic impact of tMTV-pre decreased as radiotherapy dose increased. Among patients with tMTV-pre ≤32 mL, there was no difference in survival according to radiotherapy dose delivered (p = 0.694). However, median OS was inferior in patients with tMTV-pre >32 mL who received ≤60 Gy compared with those who received 61-69 Gy or ≥70 Gy (p = 0.001).

CONCLUSIONS: Higher tMTV-pre is associated with significantly worse OS in inoperable stage III NSCLC treated with definitive CRT. Our findings suggest that for patients with large tMTV-pre, achieving a therapeutic radiation dose may help maximize OS. Prospective studies are needed to confirm this finding.