ESTRO 2024 - Abstract Book

S801

Clinical - CNS

ESTRO 2024

1 Odette Cancer Centre, Sunnybrook Health Sciences Centre, University of Toronto, Radiation Oncology, Toronto, Canada. 2 Simcoe Muskoka Regional Cancer Program, Royal Victoria Regional Health Centre, Radiation Oncology, Barrie, Canada. 3 Princess Margaret Cancer Center, University Health Network, Biostatistics Department, Toronto, Canada

Purpose/Objective:

Stereotactic body radiotherapy (SBRT) for spinal metastases improves local control and provides a higher rate of pain relief compared with conventional external beam radiotherapy (cEBRT). There is limited data on the risk of vertebral compression fracture (VCF) after spine SBRT and its predictors in the elderly. The additional frailty and comorbidities leading to reduced systemic therapy options and shorter overall survival (OS), along with reduced bone density in older patients, may impact the risk/benefit ratio specific to spine SBRT. We aim to evaluate the risk of VCF, local failure (LF) and OS in the elderly patients treated with spine SBRT.

Material/Methods:

A prospectively maintained institutional database of over 900 patients and 2300 vertebral segments treated with spine SBRT was reviewed to identify patients aged 70 or above treated from 2008 to 2021. Patients were followed with q3-monthly full spine MRI and clinical assessment. The primary endpoint was the VCF rate. Secondary endpoints included MRI-based LF and OS. OS rates were calculated using the Kaplan-Meier methods and cumulative incidences of LC and VCF were calculated per segment using the competing risk analysis method. Age as a continuous variable was used with binary partitioning methods to determine an age cut-off where the risk of VCF may start to increase.

Results:

A total of 580 spinal segments in 252 patients aged 70 or above were identified. Their baseline characteristics and treatment details are summarized in Table 1. The median age (range) and follow-up duration (interquartile range (IQR)) were 75.8 (70 – 90.3) years and 16.9 (6.5 – 41.3) months, respectively. The cumulative incidence of VCF at 6, 12 and 24 months was 6.3%, 8.7% and 12.6% respectively. Binary partitioning determined an age cut-off of 86 years where those older than 86 years had significantly higher risk of VCF (24.2% vs 5.2% at 6-month, 27.3% vs 7.6% at 12 month and 30.3% vs 11.5% at 24-month, p = 0.001, Figure 1). The median (IQR) time of onset of VCF after SBRT was 3.4 (2.6 -6.0) months for those over 86 versus 11.4 (4.0-24.0) months for those under 86. On univariate analysis (UVA), other parameters significantly associated with a higher risk of VCF included pre-existing vertebral body collapse (p=0.002), lumbar location (p=0.005), volume of the clinical target volume (CTV) (p=0.011) and D80 of the CTV (p=0.008).