Patient and Treatment Factors Associated With Improved Local Control and Survival in Oligometastatic Bone Disease: Results From a Large Single-Institution Experience Using Stereotactic Body Radiation Therapy

Limited data exist to guide optimal patient selection and treatment of bone metastases with curative intent despite the increasing application of stereotactic body radiation therapy (SBRT) for oligometastatic (OM) disease control and reirradiation (Re-RT).Clinical characteristics for 434 patients consecutively treated with bone SBRT at a single institution from March 2011 to June 2020 were analyzed by OM, spine, and nonspine bone using Cox regression to determine association with local control (LC), progression-free survival (PFS), and overall survival (OS), and the Kaplan-Meier method to estimate PFS and OS.Most patients had prostate (39%) or breast/lung (21%) cancer and 1 to 3 lesions (96%), with 651 lesions (spine 63%) treated for Re-RT (12%) or OMD (88%), including synchronous (10%), metachronous (28%), repeat (27%), or induced (23%) states as defined by The European Society for Radiotherapy and Oncology and European Organisation for Research and Treatment of Cancer criteria. Biologically effective dose (BED10) ≥50 (hazard ratio, 0.68; 95% confidence interval, 0.48-0.96; P < .03) predicted improved LC among OM lesions and planning target volume (PTV) ≥150 cc (hazard ratio, 1.94; 95% confidence interval, 1.02-3.70; P < .04) predicted worse LC for nonspine bone. Prostate histology, performance status (PS) 0 to 1, and metastasis-free interval ≥2 year predicted improved PFS and OS (P < .05). Metachronous, synchronous, or repeat OM had higher PFS and OS (P ≤ .001) than induced OM. With median follow-up 25.7 months, 1- and 2-year PFS was 63% and 47% for OM and 36% and 25% for Re-RT; 1- and 2-year OS was 87% and 73% for OM and 58% and 43% for Re-RT. Acute toxicities included grade 1 to 2 pain flare (9%) and fatigue (14%). Late toxicities included fracture (1%) for OM and myelopathy (2.5%) or nerve pain (1.2%) for Re-RT.BED10 ≥50 for OM and PTV <150 cc for nonspine bone lesions was associated with improved LC. Prostate histology, PS 0 to 1, metastasis-free interval ≥2 years, and metachronous, synchronous, or repeat presentations per The European Society for Radiotherapy and Oncology and European Organisation for Research and Treatment of Cancer criteria predicted improved PFS and OS among OM patients treated with bone SBRT.