Important Factors for Local Control After Radiotherapy of Bone Metastases in Cases of Long-Term Survivors.

PURPOSE/OBJECTIVE(S) With the advance of systemic therapy, long-term survivors have increased and importance of long-term local control of bone metastases has increased in recent years. The purpose of this study was to search for factors affecting local control of bone metastatic lesions in external-beam radiotherapy (EBRT) for cases with long-term survival of ≥1-year. MATERIALS/METHODS Between December 2010 and April 2019, 349 lesions (vertebral body, 214; pelvic, 73; rib/ sternal, 22; extremity, 35; skull, 6) in 259 patients received EBRT, and survived for ≥1-years after EBRT. Local control was evaluated by follow-up CT. Doses of EBRT were 8-50 Gy (median 30 Gy). RESULTS One and three-year control rates at EBRT sites were 95% and 86%, respectively. Local recurrence was observed in 9.7% (34 lesions in 31 patients). Sex, age of > 70, bone metastases other than vertebrae, bone metastases from unfavorable primary tumor sites (hepatobiliary/pancreatic/colorectal/thyroid/renal cell carcinoma), and without bone modified agents (BMAs) and/or systemic therapy (ST) after EBRT were statistically significant poor local control factors (P = 0.036, 0.038, 0.001, 30 Gy), bone cortex destruction and without ST before EBRT (P = 0.623, 0.887, and 0.568, respectively). In multivariate analysis, bone metastases other than vertebrae, bone metastases from unfavorable primary tumor sites and without BMAs were significant unfavorable factors for local control (P = 0.011, 0.0004, and 0.028, respectively). CONCLUSION EBRT dose escalation of > 30 Gy did not seem to be useful. Although further studies are needed, primary tumor and bone metastatic sites were associated with local control. In addition, the use of BMAs is useful in terms of local control.