RecruitingPhase 2Radiation therapyAssociation of Thoraco-mediastinal Radiotherapy With Maintenance Immunotherapy Treatment With AtezolizumabInvestigate the role of consolidative radiotherapy treatment at the thoraco-mediastinal level in the patient suffering from lung microcytoma - extensive disease and treated with chemo-immunotherapy with atezolizumab, in association with maintenance therapy with atezolizumab.