Impact of Fraction Size and Primary Tumor on Outcomes After Palliative Radiation for Osseous Metastases.

PURPOSE/OBJECTIVE(S) To review palliative RT practices, outcomes, and compare the percentage of remaining life spent receiving RT (PRLSRT) for patients treated with RT for osseous metastases. MATERIALS/METHODS A retrospective analysis was conducted using the National Cancer Database (2010-2016). Patients with bone mets who underwent palliative bone RT were included. Common palliative RT schemes (Gy/Fx) were evaluated to determine treatment patterns and outcomes. Median PRLSRT, incomplete RT courses, deaths on RT as well as 30-day and 90-day mortality rates were calculated. A logistic regression was performed to identify factors affecting completion rates. RESULTS 52,971 patients were included: 45.0% non-small cell lung (NSCLC), 15.1% breast, 10.8% prostate, 10.9% GI, 9.7% genitourinary, 4.9% small-cell lung (SCLC), and 3.3% other. Overall median survival after palliative RT was 5.74 months. Patients receiving lower dose per fraction (2Gy/Fx) were more likely to be younger and healthier, yet experienced worse palliative outcomes with higher median PRLSRT, rates of incompletion, and deaths on treatment (Table 1). Breast and prostate were most likely to complete RT (89.1% and 89.6%), while GI NOS and SCLC were least likely (77.6% and 78.6%) (P < 0.001). Upper GI patients were most likely to die on treatment (1.3%), while prostate patients were the least (0.2%) (P < 0.001). PRLSRT ≥50% was observed more frequently in GI NOS (16.6%), upper GI (10.4), NSCLC (10.3%), and skin (9.8%) compared to prostate (2.4%) and breast (2.7%) (P < 0.001). Logistic regression indicated age, race, insurance status, Charlson-Deyo score, primary site, metastatic involvement, bone RT site, and Gy/Fx were significant factors affecting completion rates of RT. Median PRLSRTs were: 14.89% GI NOS, 9.90% upper GI, 9.49% NSCLC, 7.89% skin, 7.18% SCLC, 6.12% lower GI, 5.64% GYN, 5.42% GU, 5.24% HNC, 2.05% prostate, and 2.02% endocrine, and 1.84% breast (P < 0.001). Those receiving 3Gy/Fx and 2Gy/Fx were less likely to complete RT when compared to 4Gy/Fx, with odds ratios of 1.209 and 15.023 respectively (P < 0.001). Patients with SCLC were least likely to complete RT, with a 1.694 odds ratio compared to breast (P < 0.001). CONCLUSION For palliative RT for osseous metastases, dose per fraction and primary cancer impact the palliative outcomes of PRSLRT, the likelihood of completing RT, and death during treatment and should be considered to minimize the burden of care and maximize benefits of treatment.