Stereotactic Body Radiation Therapy for Nonspine Bone Metastases: A Case-Based Radiosurgery Society Review

Purpose: Growing evidence supports stereotactic body radiation therapy (SBRT) over conventional radiation therapy for spine bone metastases, with an expanding role in nonspine bone metastases (NSBM). Our case-based review aims to inform radiation oncologists in the appropriate use of SBRT for representative cases of NSBM. Methods and Materials: Three cases were selected for discussion: (1) rib, (2) skull base, and (3) femur. Relevant literature was reviewed, and areas for future investigation were discussed. Results: SBRT can be effectively delivered in NSBM with appropriate patient selection, target volume delineation, prescription dose, organs at risk (OARs) dose constraints, and treatment planning. Conclusions: The Radiosurgery Society's case-based review offers guidance on the appropriate use of SBRT in NSBM with discussions and consensus recommendations from experts. SBRT can be considered for patients with oligometastatic disease with a favorable prognosis in whom the goal is durable local control and/or symptom relief. It can be considered for radioresistant histologies and improved OAR sparing. Available magnetic resonance imaging or positron emission tomography/computed tomography should be fused to improve target volume delineation. A clinical target volume margin, generally of 5 mm, should be considered to cover microscopic disease. As bones are easily visualized on daily images acquired for accurate and precise setup of patients, a planning target volume margin should be kept less than or equal to 3 mm. Although SBRT can be delivered in 1 fraction, fractionated SBRT may be preferred to meet dose constraints when the clinical target volume is adjacent to the OARs. NSBM of long bones that are weight bearing, lytic, or have a high MIRELS score should be evaluated by an orthopedic surgeon.