How would you treat a patient with a refractory primary splenic marginal zone lymphoma with symptomatic splenomegaly (20 cm) and a mild pancytopenia?

Prior trials of systemic therapy including alkylating agents and rituximab have failed and the patient is medically inoperable with no history of Hepatitis C. If you offer RT, what dose and target would you recommend? How often would you check a CBC and would you stop/hold treatment if the patient had worsening of cytopenia during radiation treatment?