Diagnosis of a solitary plasmacytoma requires a full workup to rule out myeloma elsewhere. This is because many patients are ultimately found to have evidence of myeloma. Following complete evaluation, patients with a solitary plasmacytoma can be treated with radiation therapy alone, as studies have indicated that the addition of chemotherapy to radiation does not improve overall survival in patients with solitary plasmacytoma. This was done in this case
Radiation therapy for solitary plasmacytoma typically delivers between 40 and 50 Gy. Treatment with radiation is associated with up to 50% of patients with solitary bone plasmacytoma being alive without evidence of recurrence 10 years from treatment, suggesting that many patients with solitary plasmacytoma can be cured. Prognosis may be even better for patients with solitary extramedullary plasmacytoma. Both osseous and extraosseous or extramedullary plasmacytomas are treated with radiation therapy.
WHen plasmacytoma was completely excised, guidelines do not recommend adjuvant radiation. From p.3 of reference 2: "...if patients have been treated by primary surgery, radiotherapy would only be required in patients with inadequate surgical margins".
Rajkumar SV, Dispenzieri A, Kyle RA. Monoclonal gammopathy of undetermined significance, Waldenström macroglobulinemia, AL amyloidosis, and related plasma cell disorders: diagnosis and treatment. Mayo Clinic Proceedings. 2006;81:693-703.