Spine stereotactic radiosurgery for the treatment of multiple myeloma

OBJECTIVE The objective of this study was to define symptomatic and radiographic outcomes following spine stereotactic radiosurgery (SRS) for the treatment of multiple myeloma. METHODS All patients with pathological diagnoses of myeloma undergoing spine SRS at a single institution were included. Patients with less than 1 month of follow-up were excluded. The primary outcome measure was the cumulative incidence of pain relief after spine SRS, while secondary outcomes included the cumulative incidences of radiographic failure and vertebral fracture. Pain scores before and after treatment were prospectively collected using the Brief Pain Inventory (BPI), a validated questionnaire used to assess severity and impact of pain upon daily functions. RESULTS Fifty-six treatments (in 38 patients) were eligible for inclusion. Epidural disease was present in nearly all treatment sites (77%). Moreover, preexisting vertebral fracture (63%), thecal sac compression (55%), and neural foraminal involvement (48%) were common. Many treatment sites had undergone prior local therapy, including external beam radiation therapy (EBRT; 30%), surgery (23%), and kyphoplasty (21%). At the time of consultation for SRS, the worst, current, and average BPI pain scores at these treatment sites were 6, 4, and 4, respectively. The median prescription dose was 16 Gy in a single fraction. The median clinical follow-up duration after SRS was 26 months. The 6- and 12-month cumulative incidences of radiographic failure were 6% and 9%, respectively. Among painful treatment sites, 41% achieved pain relief adjusted for narcotic usage, with a median time to relief of 1.6 months. The 6- and 12-month cumulative incidences of adjusted pain progression were 13% and 15%, respectively. After SRS, 1-month and 3-month worst, current, and average BPI scores all significantly decreased (p < 0.01). Vertebral fracture occurred following 12 treatments (21%), with an 18% cumulative incidence of fracture at 6 and 12 months. Two patients (4%) developed pain flare following spine SRS. CONCLUSIONS This study reports the largest series of myeloma lesions treated with spine SRS. A rapid and durable symptomatic response was observed, with a median time to pain relief of 1.6 months. This response was durable among 85% of patients at 12 months following treatment, with 91% local control. The efficacy and minimal toxicity of spine SRS is likely related to the delivery of ablative and conformal radiation doses to the target. SRS should be considered with doses of 14-16 Gy in a single fraction for patients with multiple myeloma and limited spinal disease, myelosuppression requiring "marrow-sparing" radiation therapy, or recurrent disease after EBRT.