Early response assessment of re-ossification after palliative conventional radiotherapy for vertebral bone metastases

Background: To evaluate the therapeutic outcomes in patients with bone metastases receiving radiotherapy (RT), it is important to use objective radiological response criteria. The aim of this study was to investigate the changes in pain and re-ossification after RT for painful vertebral bone metastases without paralysis by malignant spinal cord compression. Methods: The participants included 55 patients who received RT for painful vertebral bone metastases without paralysis in our institution between 2012 and 2016. Bone modifying agents (BMAs) were administered in all patients. Follow-up assessments were done just before the start of RT and at 1, 2, 3, 4, and 6 months after RT. Radiological responses of irradiated vertebrae by RT were assessed by computed tomography (CT) using MD Anderson response classification criteria (MDA criteria) and the pain response was assessed by Numeric Rating Scale (NRS). Response was classified as complete response (CR), partial response (PR), progressive disease (PD), and stable disease (SD). Results: The rates of CR were 2%, 7%, 20%, 30%, and 56% at 1, 2, 3, 4, and 6 months, respectively. The rates of CR or PR were 15%, 49%, 77%, 91%, and 91% at 1, 2, 3, 4, and 6 months, respectively. The rates of CR or PR were significantly higher in patients with breast cancer than in patients with lung cancer (p = 0.043). At one month, there was an association between the NRS and radiological response assessed by MDA criteria. There was a significant trend that, with a better response, there were more patients without pain (p = 0.021). Conclusions: Under BMAs administration, successful RT for vertebral bone metastases decreased pain and caused re-ossification. The MD Anderson criteria could be useful for assessment of radiological responses of irradiated vertebrae.