Treatment With [90]Y-Ibritumomab Tiuxetan Versus no Treatment in Patients With Follicular Non Hodgkin Lymphoma (Stage III or IV) Having Achieved a Partial or Complete Remission After First Line Chemotherapy

Inclusion Criteria: * Non Hodgkin Lymphoma stage III or IV at timepoint of diagnosis * Patients who have achieved a remission after first line chemotherapy * No less than 6 weeks and no more than 12 weeks since last dose of chemotherapy * older than 18 years * written informed consent Exclusion Criteria: * Any other anticancer treatment for NHL except the preceding first line chemotherapy * Prior radiation therapy * Patients who have not recovered from the toxic effects of the first line chemotherapy * Any other cancer or history of cancer less than 10 years ago * Patients with known HIV positivity * patients with pleural effusion or ascites * female patients who are pregnant or breast feeding (women of childbearing potential must have a negative serum pregnancy test at study entry) * Adults not employing an effective method of birth control during study treatment and 12 months thereafter * Patients unable or unwilling to comply with protocol