Inclusion Criteria:

- Histologic documentation of diffuse large B-cell lymphoma, or any of its variants as
defined in the WHO classification

- Completion of at least 4 cycles of a rituximab-containing, anthracycline-based
combination chemotherapy

- Negative post-chemotherapy (or interim) PET scan

- Absolute neutrophil count greater than 1500 and platelet count greater than 40,000

- Negative pregnancy test in women of child-bearing potential

For patients with HIV/AIDS, the following must be true:

- The patient is compliant on combination anti-retroviral therapy (CART)

- The patient has CD4 count ≥ 200 at time of diagnosis

Exclusion Criteria:

- Any contraindications to irradiation

- Primary CNS lymphoma

- HIV/AIDS