Bone density and pain response following intensity-modulated radiotherapy versus three-dimensional conformal radiotherapy for vertebral metastases - secondary results of a randomized trial

BACKGROUND: This was a prespecified secondary analysis of a randomized trial that analyzed bone density and pain response following fractionated intensity-modulated radiotherapy (IMRT) versus three-dimensional conformal radiotherapy (3DCRT) for palliative management of spinal metastases. METHODS/MATERIALS: Sixty patients were enrolled in the single-institutional randomized exploratory trial, randomly assigned to receive IMRT or 3DCRT (30 Gy in 10 fractions). Along with pain response (measured by the Visual Analog Scale (VAS) and Chow criteria), quantitative bone density was evaluated at baseline, 3, and 6 months in both irradiated and unirradiated spinal bodies, along with rates of pathologic fractures and vertebral compression fractures. RESULTS: Relative to baseline, bone density increased at 3 and 6 months following IMRT by a median of 24.8% and 33.8%, respectively (p < 0.01 and p = 0.048). These figures in the 3DCRT cohort were 18.5% and 48.4%, respectively (p < 0.01 for both). There were no statistical differences in bone density between IMRT and 3DCRT at 3 (p = 0.723) or 6 months (p = 0.341). Subgroup analysis of osteolytic and osteoblastic metastases showed no differences between groups; however, mixed metastases showed an increase in bone density over baseline in the IMRT (but not 3DCRT) arm. The 3-month rate of the pathological fractures was 15.0% in the IMRT arm vs. 10.5% in the 3DCRT arm. There were no differences in pathological fractures at 3 (p = 0.676) and 6 (p = 1.000) months. The IMRT arm showed improved VAS scores at 3 (p = 0.037) but not 6 months (p = 0.430). Using Chow criteria, pain response was similar at both 3 (p = 0.395) and 6 (p = 0.732) months. CONCLUSIONS: This the first prospective investigation evaluating the impact of IMRT vs. 3DCRT on bone density. Along with pain response and pathologic fracture rates, significant rises in bone density after 3 and 6 months were similar in both cohorts. Future randomized investigations with larger sample sizes are recommended. TRIAL REGISTRATION: NCT, NCT02832830. Registered 14 July 2016