Randomized, Open-label, Two-arms, Phase III Comparative Study Assessing the Role of Involved Mediastinal Radiotherapy After Rituximab Containing Chemotherapy Regimens to Patients With Newly Diagnosed Primary Mediastinal Large B-Cell Lymphoma

Inclusion Criteria: * Previously untreated primary mediastinal diffuse large B-cell lymphoma, CD20 positive. * Patients must have histological confirmation of the diagnosis (it is recommended that the immunohistochemical panel includes: CD45, CD20, CD30, CD15, CD10, BCL6, BCL2, MUM-1), and in addition have a dominant mass within the anterior mediastinum. * No evidence of extranodal disease outside the chest including spleen and bone marrow. * Age at least 18 years. * Fit to receive chemotherapy and radiotherapy with curative intent. * Patients will be eligible if the treatment phase consisting in a Rituximab combined with any anthracycline-containing chemotherapy regimen without consolidation with autologous stem cell support (e.g., 6 cycles of CHOP14-21, DA-EPOCH, Mega-CHOP or 12 weeks of VACOP-B or MACOP-B). * At least 6 courses of Rituximab should be administered * Able and willing to give informed consent, and to undergo staging including PET scanning * Willingness to comply with an appropriate contraceptive method in women of childbearing potential or men. * Histological diagnostic material available for review. Exclusion Criteria: * History of malignancy other than squamous cell carcinoma, basal cell carcinoma of the skin or carcinoma in situ of the cervix within the last 5 years. * Evidence of clinically significant cardiac disease at diagnosis, as defined by history of symptomatic ventricular arrhythmias, congestive heart failure or myocardial infarction within 12 months before study entry. Cardiac impairment due to local extension of lymphoma will not be an exclusion criterion in the absence of other cardiac disease. * Known HIV-positive serology. * Pregnant or lactating women. * Any psychological, familial, sociological or geographical condition potentially hampering compliance with the study protocol and follow-up schedule.