Room: Exhibit Hall
Purpose: To report clinical outcomes in patients with metastatic cancer following stereotactic body radiotherapy (SBRT) to vertebral spine metastases with assessment of dose-volume associations to late toxicity and pain relief.
Methods: A single-institution retrospective analysis of 123 metastatic vertebral spine lesions in 89 patients treated with 1, 3 or 5 fraction SBRT course between 2011-2017 was performed. Median clinical follow up was 19.6 months (range: 4.8-73.2) with 63% of patients receiving follow up imaging at 17.4 months (range: 1.1-70.0). Late toxicities, including vertebral compression fracture (VCF), per CTCAE v5.0 and patient reported pain relief (change in brief pain inventory scale) were recorded. Data was used to test a previously published myelopathy probability model. Dosimetric variables were extracted from the plans to use in logistic regression to determine predictors of toxicity.
Results: A total of 16 (13.0%) and 13 (10.6%) patients experienced 2 grade toxicity and VCF, respectively. Sixty-seven (54.5%) patients reported pain relief with mean pain relief of 5 (range: 1-10) on the 10-point BPI scale. Overall local control was 86.2%. One case of grade 2 asymptomatic radiographic myelitis was observed. The model indicated >5% myelitis risk based on dosimetric data. Biological effective dose (BED3) for the spinal cord and maximum point target dose within the vertebral elements were associated with pain relief (P=0.047) and VCF (P=0.042), respectively. Fracture risk of 6.2-19.2% from maximum point target dose of 21.6-42.4 Gy was calculated from the data.
Conclusion: SBRT treatment for spine metastases was associated with moderate risk of late toxicity and VCF while achieving high local control. Greater BED and maximum point target dose were associated with patient-reported pain relief and VCF. The extracted dose-dependent fracture risk shows agreement with other studies. The data set will be used to test existing and further develop models to ensure safe SBRT practice.