Background: There have been reports on the use of hypofractionated stereotactic body radiotherapy (SBRT) for bone plasmacytomas, but no prospective data are available. We present the initial analysis of an ongoing prospective protocol on SBRT addressing the feasibility and safety of this treatment for solitary bone plasmacytomas. Patients and Methods: A prospective cohort of SBRT for solitary bone plasmacytoma was developed. Patients could receive different doses depending on the index bone, from single fraction for skull base lesions, 24 Gy in 3 fractions for spine lesions, and 30 Gy in 5 fractions for other bones. Overall survival, bone events, local control, and progression to multiple myeloma (MM) were measured and compared to our retrospective cohort of patients treated with conformal standard-dose radiotherapy. Quality of life was assessed via the EORTC QLQ-C30 questionnaire, and toxicities were assessed by the CTCAE v5.0 criteria. After 1 year or the inclusion of 5–10 patients, a feasibility and safety analysis was programmed. Results: Between April 2018 and April 2019, 5 patients were included. All were male, with a median age of 53.1 years. The median follow-up was 21.8 months. No patient had local progression, bone event, or died. Two patients had progressions to MM. The mean survival free of progression to MM was 18.6 months, compared to 19 months in the retrospective cohort; median values were not reached. There were no grade 3 toxicities. Conclusion: SBRT for plasmacytoma is safe and feasible. More robust data are awaited.