The impact of residual metabolic primary tumor volume after completion of thoracic irradiation in patients with inoperable stage III NSCLC.

Abstract

9049 Background: The metabolic tumor volume (MTV) is a functional and volumetric PET/CT parameter that has been investigated in recent years with respect to its predictive and prognostic value in different tumor entities. In this study, we investigated the role of residual MTV after completion of thoracic irradiation in inoperable stage III non-small cell lung cancer (NSCLC). Methods: We analyzed retrospective and prospective data of 56 patients with inoperable stage III NSCLC treated with chemoradiotherapy (CRT) and chemoradioimmunotherapy (CRT-IO). All patients received an 18F-FDG-PET/CT 3 to max. 6 months after completion of thoracic irradiation. The measurement of the residual MTV of the primary tumor was performed by calculating the SUVmean of the liver + 2SD as threshold. The patients were divided into the following groups: residual-MTV < 1ml; residual-MTV 1-25ml and residual-MTV > 26ml. Survival, local recurrence, and distant metastasis rates were calculated using the Kaplan-Meier method from the last day of thoracic irradiation. Results: The median follow-up was 45 months (range 16-74) in the CRT group and 16 months in the CRT-IO group (range13-19). Twenty-two (39%) patients had a residual MTV < 1ml (1st group), 19 (34%) a residual MTV between 1-25ml (2nd group) and 15 (27%) a residual MTV > 25ml (3rd group) after completion of thoracic irradiation. Median overall survival was 61, 20 and 12 months (p = 0.006) in the 1st, 2nd and 3rd groups, respectively. 12-month survival was 86%, 50% and 33% after CRT vs. 88%, 71% and 50% after CRT-IO in the 1st, 2nd and 3rd groups, respectively. The median time to in-field recurrence in the 1st, 2nd and 3rd groups was 51, 20 and 15 months (p = 0.011). The prognostic value of the residual MTV on OS was confirmed exclusively in the CRT patient cohort (p = 0.04), but not in the CRT-IO patient cohort (p = 0.174). Residual MTV demonstrated no influence on the local recurrence rate in the CRT-IO patient cohort, but only in patients treated with CRT (p = 0.007). Conclusions: Patients with inoperable stage III NSCLC in whom the residual MTV was < 1ml after completion of thoracic irradiation showed significantly better survival than patients with a residual MTV of 1-25ml and MTV > 25ml. The subgroup analysis confirmed the prognostic value of residual MTV only in patients who received chemoradiotherapy without consolidation immunotherapy.