Characteristics and Predictors of Radiographic Local Failure in Patients With Spinal Metastases Treated With Palliative Conventional Radiotherapy

Abstract

Background: Local control of spinal metastases is an important issue for patients who may live long enough to experience cancer recurrence. However, the literature on patterns of radiographic local failure among patients with spinal metastases receiving conventional radiotherapy (RT) is sparse. The purpose of this study was to evaluate the rates, consequences, and predictors of radiographic local failure in patients with spinal metastases managed with palliative conventional RT alone, in order to guide clinical decision-making and counsel patients treated with this modality of RT. Methods: We retrospectively reviewed 296 patients with spinal metastases treated with palliative conventional RT at the Brigham and Women’s Hospital/ Dana-Farber Cancer Institute. Of these patients, 182 had follow-up computed tomography (CT) or magnetic resonance (MR) imaging and were included in local failure analyses. We assessed the presence of and time to development of radiographic local failure, defined as radiological progression within the treatment field. We also evaluated consequences of and interventions for local failure. Kaplan-Meier analyses determined overall survival (OS) estimates. Cumulative incidence estimates determined local failure rates, with death considered a competing risk. Cox regression analyses tested predictors of local failure. Results: The median OS for all 296 patients was 4.0 months. The median OS was 1.0 month for the 114 patients without follow-up imaging versus 7.7 months for the 182 patients with follow-up imaging. Patients received a median of 30 Gy in 10 fractions to a median of 4 vertebral bodies. Overall, 74 of 182 patients (40.7%) experienced local failure. The 6-month, 12-month, and 18-month local failure rates were 26.5%, 33.1%, and 36.5%, respectively, while corresponding rates of death were 24.3%, 38.1%, and 45.9%. The median time to local failure was 3.8 months. Of those with local failure, 51.4% had new compression fractures, 39.2% were admitted for pain control, 28.4% developed neurological symptoms, and 17.6% developed cord compression; the median time from RT to each of these events were 3.0 months, 5.7 months, 10.5 months, and 9.0 months, respectively. Interventions for local failure included reirradiation (35.1%), invasive interventions for pain control (14.9%), salvage surgery (10.8%), and vertebroplasty (6.8%). On multivariable analysis, independent predictors of local failure included single-fraction RT (8 Gy) (HR = 2.592 [95% CI 1.437-4.675], p = 0.002), lung histology (HR = 3.568 [95% CI 1.532-8.309], p = 0.003), and kidney histology (HR = 4.937 [95% CI 1.529-15.935], p = 0.008). Conclusions: Patients experience a >30% rate of radiographic local failure by 1-year after conventional RT and often require admissions for pain control and re-treatment. Single-fraction RT and lung or kidney histology predicted local failure. Given the high rates of local failure for patients with favorable prognosis, assessment of the risk of death and progression versus risk of local failure is important for guiding clinical decisions regarding treatment modality and fractionation.