• Patients with polymetastatic cancer defined as more than 5 sites of radiographically-evident systemic metastatic disease (excluding intracranial disease)

• High-risk asymptomatic bone metastasis(es) (Brief Pain Inventory \[BPI\] score of \< 5 on the maximum pain item) defined as fulfilling at least one of the following four high-risk criteria:

‣ Bulky site of disease in bone ( ≥ 2 cm);

⁃ Disease involving the hip (acetabulum, femoral head, femoral neck), shoulder (acromion, glenoid, humeral head), or sacroiliac joints;

⁃ Disease in long bones occupying up to 2/3 of the cortical thickness (humerus, radius, ulna, clavicle, femur, tibia, fibula, metacarpals, phalanges); and/or

⁃ Disease in junctional spine (C7-T1, T12-L1, L5-S1) and/or disease with posterolateral element (pedicles and/or facet joints) involvement

⁃ NOTES: Patients may have up to 3 individual high-risk bone metastases enrolled in the study. Sternum, rib, and scapula are defined as flat bones so lesions in these locations would only be included if bulky

• Patients with any solid tumor type (excluding multiple myeloma)

• Patients must have systemic disease evaluation through standard of care diagnostic imaging, including either CT chest/abdomen/pelvis or body positron emission tomography (PET)/CT, with radiology report available

• Patients with treated brain metastases and no known leptomeningeal disease are eligible if these lesions have been treated prior to enrollment

• Age ≥ 18

• Performance status: Eastern Cooperative Oncology Group (ECOG) 0-2 or Karnofsky performance status (KPS) ≥ 60

• No previous radiotherapy to the intended enrolled sites of disease

• No epidural spinal cord compression (ESCC) ≥ grade 1c (defined as deformation of the thecal sac with spinal cord abutment) at the enrolled bone metastasis(es)

• No prior fracture at the enrolled bone metastasis(es)