Study of Interest of Personalized Radiotherapy Dose Redistribution in Patients With Stage III NSCLC

The investigators objective is to determine whether tumour radiotherapy dose escalated up to 74 Gy in 6.6 weeks can improve the disease Local Regional Control rate at 15 months (1 year after completion of RCT) by adapting radiotherapy target volume to the metabolic response as assessed on FDG-PET/CT performed at 42 Gy of concomitant radio-chemotherapy in stage III non-small cells lung cancer and warrant more extensive phase III study. Eligible patients will be allocated to one of 2 treatment groups: * Arm A: Patients in the experimental arm will receive an individualized radiotherapy prescription up to a total dose of 74 Gy given in 6.6 weeks if they have a positive FDG-PET at 42Gy. * Arm B: Patients in the standard arm will receive a single prescription of 66 Gy in 33 fractions in 6.6 weeks, with 2 Gy fractions given once daily, 5 days a week, without target volume reduction or adaptation (whatever the FDG-PET result). In both arms, all patients will undergo 2 cycles of induction chemotherapy (based platinum salts) and a curative radio-chemotherapy. In both arms all fields must be treated daily.