Local control of bone metastasis treated with palliative radiotherapy in patients with lung cancer: An observational retrospective cohort study.

Bone metastasis is common in advanced lung cancer, with the incidence reported to be 30%, and radiotherapy (RT) is used for pain relief from bone metastasis. The present study aimed to identify factors affecting local control (LC) of bone metastasis from lung cancer and to assess the significance of moderate RT dose escalation. This was a retrospective cohort study, where LC of bone metastasis from lung cancer that had received palliative RT was reviewed. LC at RT sites was evaluated with follow-up computed tomography (CT). The influence of treatment-, cancer- and patient-related risk factors for LC was assessed. A total of 317 metastatic lesions in 210 patients with lung cancer were evaluated. The median RT dose (biologically effective dose calculated using an α/β of 10 Gy; BED10) was 39.0 Gy (range, 14.4-50.7 Gy). The median follow-up time for survival and median radiographic follow-up time were 8 (range, 1-127) and 4 (range, 1-124) months, respectively. The 0.5-year overall survival and LC rates were 58.9 and 87.7%, respectively. The local recurrence rate in RT sites was 11.0%, and bone metastatic progression, except in RT sites, was observed in 46.1% at the time of local recurrence or the last follow-up CT of the RT sites. According to multivariate analysis, RT sites, pre-RT neutrophil to lymphocyte ratio (NLR), post-RT non-administration of molecular-targeting agents (MTs), and non-administration of bone modifying agents (BMAs) were significant unfavorable factors for LC of bone metastasis. Moderate RT dose escalation (BED10 >39 Gy) tended to improve the LC of RT sites. In cases without MTs, moderate dose escalation of RT dose improved the LC of RT sites. In conclusion, treatment (post-RT MTs and BMAs), cancer (RT sites) and patient (pre-RT NLR)-related risk factors had a large impact on improving the LC of RT sites. Moderate RT dose escalation seemed to have a small impact on improving the LC of RT sites.