Classification of patients with painful tumors to predict the response to palliative radiotherapy

Purpose This study aimed to identify factors affecting pain response to develop a patient classification system for palliative radiotherapy. Methods and Materials Our prospective observational study (XXXXX) provided data on patients who received palliative radiotherapy for painful tumors. The eligibility criteria were that the numerical rating scale (NRS) was 2 or more before treatment, and palliative radiotherapy was performed between August 2021 and September 2022. Post-radiotherapy follow-up was scheduled prospectively at 2, 4, 12, 24, 36, and 52 weeks. Pain response was assessed using the International Consensus Pain Response Endpoints, with the primary outcome being the response rate within 12 weeks. Multivariable logistic regression was performed to identify factors affecting pain response and develop the classification system. Each class evaluated the differences in response rate, time to response, and progression. Results Of the 488 registered lesions, 366 from 261 patients met the criteria. Most patients had bone metastases (75%), with 72% using opioids and 22% were re-irradiation cases. Conventional radiotherapy (e.g., 8 Gy single fraction, 20 Gy in 5 fractions) was administered to 93% of patients. Over 6.8 months median follow-up, the average NRS decreased from 6.1 to 3.4 at 12 weeks for 273 evaluable lesions, with a 60% response rate. Opioid use and re-irradiation negatively impacted the response rate in multivariate analysis (P<0.01). Lesions were categorized into class 1 (no opioids, no re-irradiation, 89 lesions), class 2 (neither class 1 nor 3, 211 lesions), and class 3 (opioids and re-irradiation, 66 lesions), with respective response rates of 75%, 61%, and 36% (P<0.001). Time to response was similar across classes (P = 0.91), but progression rates at 24 weeks were different (11%, 27%, 63%, P<0.001). Conclusions Opioid use and re-irradiation were identified as factors leading to significant variations in pain response rates and time to progression.