Evaluation of Factors Affecting Local Failure of Radiation for Long Bone Metastasis Following Orthopedic Stabilization

Abstract

For patients with long-bone metastases who undergo orthopedic stabilization followed by radiotherapy (RT), it is unclear what extent of hardware coverage by the radiation field is needed for optimal tumor control. We investigated factors that contribute to tumor recurrence in a long bone after orthopedic stabilization and RT. One hundred one patients with 107 long-bone metastases managed with orthopedic stabilization followed by RT at our institution from 8/2011 to 3/2017 were included. Patients who did not receive RT within 4 months following orthopedic stabilization and those who did not have follow up imaging at least 3 months following completion of RT were excluded. Local failure (LF) was defined as any in-bone recurrence, whether in-field or out-of-field from radiation. Univariate analysis (UVA) assessing relation of various factors to LF was performed for age, time from surgery to RT, tumor histology, biologically effective dose using an alpha/beta of 10 (BED10; < vs ≥ 39Gy), extent of orthopedic hardware included in RT field (whole vs partial), and which bone contained metastasis. LF among patients with whole versus partial hardware coverage by RT was estimated with the Kaplan-Meier (KM) method and compared using the log-rank test. Median follow-up was 12.3 months (range 2.8 - 47.5). Median time to RT was 1.4 months (range 0.2 – 3.9) and median BED10 was 39 (range 14.4 – 59.5). There were 53 bones (49.5%) that received RT to whole hardware, while 54 (50.5%) received partial hardware RT. Long-bone metastases were located in femur (69%), humerus (21%), tibia (8%), radius (1%), and ulna (1%); 56% were right-sided and 44% left-sided. There were 23 local failures (21.5%) with median time to failure 9.6 months (range 2.8 – 27.2). In bones treated to whole hardware there were 9 local failures (17.0%), while there were 14 local failures (25.9%) in bones treated to partial hardware. Among the 14 local failures in partial hardware treatment, 5 failures were out-of-field or marginal (9.3%). On UVA, LF was not associated with age, time from surgery to RT, tumor histology, BED10, extent of orthopedic hardware coverage, or which bone contained metastasis. KM analysis and log-rank testing showed no statistically significant difference (p=0.30) in freedom from local failure for patients with whole versus partial hardware coverage. This analysis did not find a significant association between extent of hardware coverage and LF, indicating that whole hardware coverage may not be required for treatment of bone metastasis following surgical stabilization. Further study is needed to evaluate what factors may play a role in LF among patients receiving radiation for long bone metastasis following orthopedic stabilization.