Rituximab With or Without Yttrium Y-90 Ibritumomab Tiuxetan in Treating Patients With Untreated Follicular Lymphoma

Inclusion Criteria: * Histological confirmation of follicular lymphoma grades I, II diagnosed within 12 months (365 days) prior to registration; NOTE: the day of biopsy should be used as day 1 of diagnosis for this calculation * Stage I, II, III, or IV disease; NOTE: stage I disease are eligible only if the disease is not amenable to external beam radiation therapy * No indication for chemotherapy; candidate for observation * Measurable disease by tumor imaging with at least one lesion \>= 1.5 cm in at least one dimension * Previously untreated; NOTE: this includes any chemotherapy or immunotherapy or RIT; patients who received corticosteroids for diseases other than lymphoma are eligible as long as prednisone dose is =\< 10 mg/day * Low tumor burden as defined by Groupe d'Etudes des Lymphomes Folliculaires (GELF) criteria (2): * No tumor mass (nodal or extranodal) \>= 7 cm in one dimension on computed tomography (CT) * Fewer than 3 (2 or less) nodal masses \> 3 cm * No systemic or B symptoms * No splenomegaly greater than 16 cm by CT scan * No risk of organ compression - ureteral, orbital, neurological, gastrointestinal * No leukemic phase (\> 5.0 x 10\^9/L circulating FL cells in the blood as detected by complete blood count \[CBC\] with differential and smear) * No cytopenias - absolute neutrophil count (ANC) \< 1000 or platelets \< 100,000 * Meet standard criteria for RIT: * \< 25% marrow involvement with FL * No evidence of myelodysplasia * Eastern C…