Early response assessment of palliative conventional radiotherapy for painful uncomplicated vertebral bone metastases

Background: Radiation therapy (RT) is the common treatment for painful vertebral bone metastases without paralysis by malignant spinal cord compression. However, no studies have focused on the time course of pain after RT. Then, we investigated the change of pain after RT for painful vertebral bone metastases without paralysis. Methods: Participants included 101 patients who received RT for painful vertebral bone metastases without paralysis in our institution between 2012 and 2016. All patients received RT and pain response was evaluated by Numeric Rating Scale (NRS). Follow-up assessments were performed just before the start of RT and every month for six months after RT. Pain response was classified as complete response (CR), partial response (PR), pain progression (PP), and indeterminate response (IR) based on the response criteria of International Bone Metastases Consensus Working Party. Responders were classified as either CR or PR, and non-responders as either PP or IR. Results: Median NRS scores for pain were 5 before RT, decreasing to 0 by one month after RT and remaining zero until last follow-up, representing a significant decrease over time (P < 0.001). The rate of responders at each month from one to six months was 93, 96, 95, 100, 98, and 96%, respectively. Multivariate analysis revealed that Spinal Instability Neoplastic Score (SINS) was the only risk factor for response to RT at one month. At one month pain disappeared in 88% of the patients with spinal stability (SINS < 7), although pain disappeared 58% of the patients with spinal instability (SINS ≥ 7), which was significant (P = 0.002). Conclusions: Pain decreased significantly over time and 93% of patients were classified as responders as early as one month after RT in patients with painful vertebral bone metastases without paralysis. Pretreatment SINS could be a predictor of pain response to RT.