PRIMARY OBJECTIVES:
I. To estimate the maximally tolerated dose of fludarabine that can be combined with 131I-anti-CD20 (iodine I 131 tositumomab) delivering =\< 27Gy to critical normal organs followed by autologous or syngeneic transplantation in patients \>= 60 years of age with relapsed B-NHL.
SECONDARY OBJECTIVES:
I. To assess the overall and progression-free survival of the above regimen in such patients.
II. To evaluate the response rates of the above therapy.
III. To evaluate the toxicity and tolerability of the above therapy.
IV. To evaluate the feasibility of delivering concurrent high-dose radioimmunotherapy (RIT) and chemotherapy.
OUTLINE: This is a dose-escalation study of fludarabine phosphate as used in combination with I 131 tositumomab and stem cell transplant.
Patients receive a dosimetric dose of iodine I 131 tositumomab intravenously (IV) over 40-60 minutes on day -24 followed by gamma camera imaging over the next 6 days. Patients then receive a therapeutic dose of iodine I 131 tositumomab via central line over 40-60 minutes on day -14. Patients also receive fludarabine phosphate IV once daily (QD) on days -11 to -9 OR days -11 or -7. Patients undergo autologous or syngeneic peripheral blood stem cell transplantation on day 0.
Patients with circulating lymphoma cells by peripheral smear receive tositumomab IV over 1 hour OR rituximab IV over 1 hour followed by tositumomab IV over 1 hour before the dosimetric iodine I 131 tositumomab infusion.
After completion of study treatment, patients are followed up at 1, 3, 6, and 12 months and then annually thereafter.
