The Important Factor in Local Control of Bone Metastatic Lesions in Radiotherapy

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With the advance of systemic therapy, long-term survivors have increased and long-term local control of bone metastases are required for some of patients. The purpose of this study was to search for factors affecting local control of bone metastatic lesions in external-beam radiotherapy (EBRT). Between January 2010 and December 2019, 361 osteolytic bone metastases (spinal column, 192; pelvis, 87; rib/sternum, 35; extremity, 41; facial, 6) in 257 patients received EBRT. Local control was evaluated by follow-up CT. Doses of EBRT were 8-50 Gy (median 30 Gy). One and three-year overall survival rates were 59% and 33%, respectively. One and three-year control rates at EBRT sites were 78% and 67%, respectively. Local recurrence was observed in 18% (64 lesions) and the time of recurrence were 0.5-105 months (median 3 months). Male, age of > 70, rib/sternum and facial bone metastases, bone metastases from hepatobiliary/pancreatic/colorectal carcinoma, extraosseous invasion, EBRT ≤ 20 Gy, no use of bisphosphonates/receptor activator of NF-κB ligand (RANKL) formulation, and no use of systemic therapy after EBRT were statically significant unfavorable factors for local control (p = 0.0155,0.0005, <0.0001, <0.0001, 0.0361, 0.0010, <0.0001, and 0.0008, respectively). In multivariate analysis, age of > 70, rib/sternum/facial bone metastases, bone metastases from hepatobiliary/pancreatic/colorectal carcinoma, EBRT ≤ 20 Gy, and no use of bisphosphonates/RANKL formulation were significant unfavorable factor for local control (p = 0.0001, <0.0001, 0.0006, 0.0010, and 0.0349, respectively). For patients who can expect long-term survival, the use of bisphosphonates/RANKL formulation and higher dose EBRT seemed to be useful. Although further studies are needed, it seemed to be comparatively difficult to control bone metastases of elderly patients, rib/sternal/facial bone, hepatobiliary/pancreatic/colorectal carcinoma.