Factors affecting local control of bone metastases from radioresistant tumors treated with palliative external beam radiotherapy

Background This study aimed to evaluate the factors that affect the local control (LC) of bone metastases from radioresistant carcinomas (renal cell carcinoma, hepatocellular carcinoma [HCC], and colorectal carcinoma [CRC]) treated with palliative external-beam radiotherapy (EBRT). Methods and materials Between January 2010 and December 2020, 211 bone metastases in 134 patients were treated with EBRT in two hospitals (a cancer center and university hospital). Based on follow-up CT, these cases were reviewed retrospectively to evaluate LC at the EBRT site. Results The median EBRT dose (BED10) was 39.0 Gy (range, 14.4–66.3 Gy). The median follow-up time of the imaging studies was 6 months (range, 1–107 months). The 0.5-year overall survival and LC rates of the EBRT sites were 73% and 73%, respectively. Multivariate analysis revealed that the primary sites (HCC/CRC), low EBRT dose (BED10) (≤ 39.0 Gy), and non-administration of post-EBRT bone modifying agents (BMAs) and/or antineoplastic agents (ATs) were statistically significant factors that negatively affected the LC of EBRT sites. In the absence of BMAs or ATs, the EBRT dose (BED10) escalation from 39.0 Gy improved the LC of EBRT sites. Based on ATs administration, the LC of EBRT sites was significantly affected by tyrosine kinase inhibitors and/or immune checkpoint inhibitors. Conclusions Dose escalation improves LC in bone metastases from radioresistant carcinomas. Higher EBRT doses are needed to treat patients for whom few effective systemic therapies remain available.