Robust Correlation between Immediate Post Radio-Chemotherapy FDG PET Response and Clinical Outcome and Impact of Salvage Radiation for Partial Metabolic Responders in Locally Advanced Non–Small Cell Lung Cancer

Abstract

Only living cells retain FDG. Thus, residual cancer after radiotherapy (RT) or radio-chemotherapy (RTCT) can be detected with FDG PET. Goal of this study was to investigate correlation between tumor metabolic response measured with immediate post radio-chemotherapy (RTCT) FDG PET and clinical outcome and importance of salvage radiation for partial metabolic responders. A cohort of patients who underwent FDG PET/CT 8 days post-RT or RTCT for locally advanced non-small cell lung cancer (LANSCLC) and their subsequent therapy including salvage RT for partial metabolic response were retrospectively analyzed. Tumor metabolic response was graded with a 3-level visual scale method with levels 1 and 2 being FDG uptake lower than or comparable to noncardiac mediastinal structures (NCMS) and considered complete metabolic response (CMR) and level 3 being higher than NCMS and regarded as partial metabolic response (PMR). RTCT comprised a median total dose of 63 Gy in 35 fractions (F) over a 6-wk period and 2-4 cycles of cisplatin-based concurrent chemotherapy. Salvage RT administered a median dose of 12.5 Gy/5 F to only residual FDG avid tumor volume. A total of 41 patients treated between 2010 and 2016 were available for the data analysis. Patient demographics comprised median age 67 years (47-86) and gender ratio 23 men and 18 women. Tumor extent by AJCC included stage IIB (n=6), IIIA (n=14), IIIB (n=19) and IV (n=2) via a resected oligo metastasis in the brain. All patients had biopsy confirmed NSCLC. According to the visual score for metabolic response, 14 and 27 patients attained CMR (Group A) and PMR respectively. Among the 27 with PMR, 14 patients received salvage RT to residual FDG avid tumor volume (Group B) and the remaining 13 patients elected to receive consolidation chemotherapy (Group C) without additional RT. There was one grade 3 and no grade ≥ 4 toxicity among all patients.Abstract 3061; Table 1Group AGroup BGroup CNumber of patients141413Median progression free survival (month)27 (6-78)16 (4-68)7 (6-16)Median overall survival (month)38 (6-78)23 (8-82)11 (6-56)Local tumor control14/148/143/13The log-rank test comparing groups: A to B p=0.03; A to C p=0.002; and B to C p=0.2. Open table in a new tab The log-rank test comparing groups: A to B p=0.03; A to C p=0.002; and B to C p=0.2. The results suggest that immediate post-therapy FDG PET may help separate patients with CMR from PMR. While patients with PMR may benefit from salvage RT, CMR patients may be saved from escalated radiation dose, its toxicities and cost. Clinical trials are needed for validation of immediate post-therapy FDG PET/CT for its potential in guiding individualized therapy.