Patients in all arms undergo restaging of their disease after courses 3 and 6 of R-CHOP. Patients with stable disease after 6 courses or disease progression after courses 3 or 6 proceed to salvage chemotherapy off study. Patients achieving a partial remission or an unconfirmed CR after 6 courses undergo additional restaging 4 weeks later. Patients with disease progression proceed to salvage chemotherapy off study. Patients who achieve CR after 6 courses of R-CHOP or have a confirmed CR after the additional restaging undergo radiotherapy according to randomization (as above).