1291O Radiotherapy boost to 74 Gy based on FDG-PET at 42 Gy of radiochemotherapy (RCT) in patients with inoperable stage III non-small cell lung cancer (RTEP7 – IFCT 1401): A prospective multicentre, open-label, randomised, controlled trial

To assess the possibility and safety of a boost delivery up to74 Gy, based on lung tumour early response to on-treatment FDG-PET /CT (42 Gy), in inoperable patients with stage III non-small-cell lung cancer (NSCLC)treated with concomitant radio-chemotherapy (RCT). 158 patients were prospectively included in a multicentre phase II-III study. Patients were randomized into two groups: patients from arm A (experimental) with residual metabolism on FDG-PET2 at 42 Gy received a radiation boost (74 Gy), while patients without residual uptake on FDG-PET2 at 42 Gy and patients in arm B (standard) received a standard radiotherapy (RT) dose (66 Gy). Local control rate (LCR%), median overall survival (OS, months), and progression-free survival (PFS) were analysed for three years after the end of RCT. FDG-PET parameters were measured at baseline (PET1), 42 Gy (PET2), and 6 months post-RCT (PET3). All patients were evaluated with the RECIST 1.1 criteria. The main objective was the LCR at 1 year after RCT. Patient demographic characteristics and FDG-PET parameters were similar between the two arms (A vs. B). The mean age was 62.3 years; 53.2% of lesions were stage IIIA and 45.6% were stage IIIB. The mean radiation dose was 71.65 Gy for experimental arm and 66 Gy for standard arm (p < 0.001). The median follow-up time was 45.1 months. The LCR at 1 year after RCT was 77.6% [95% CI: 67.6% – 87.6%] in arm A and 71.2% [95% CI : 60.8% - 81.6%] in arm B. The median OS and the PFS (months) were respectively NR [95% CI: 40.9 – NR] in arm A and 43.3 [95% CI: 33.4 - NR] in arm B, and 22.3 [95% CI: 14.8 – 33.7] in arm A and 12.3 [95% CI : 9.4 – 23.3] in arm B. Using multivariate analysis, ΔSUVmax > 66% (p < 0.01), Δ metabolic tumoral volume (MTV) > 100% (p = 0.04) between PET1 and PET3, and the boost realization (p = 0.05) were the only predictors of PFS. There were less acute or late toxicity in boost radiation arm. Boost at 74 Gy based on interim FDG-PET is feasible and safe during thoracic RCT, without acute or late toxicity. Boost administration, ΔSUVmax, ΔMTV seem to be prognostic factors in patients with stage III inoperable NSCLC.