A prospective analysis of CT density measurements of bone metastases after treatment with zoledronic acid

Objective The objective was to prospectively determine CT density changes in bone metastases, before and after intravenous zoledronic acid for a maximum period of 12 months. Patients and methods Twenty-three consecutive patients presented with bone metastases and underwent therapy with zoledronic acid from December 2004. All patients underwent CT of the chest, abdomen, and pelvis. Bone density, measured in Hounsfield units (HU), was determined by segmenting lesions in the same anatomical area of the metastasis sites on the axial images of the sequential series of CT examinations. The effects of zoledronic acid were evaluated by calculating absolute and relative increases in bone density. Results The patients presented with multiple metastases in 65% of the cases. When compared with the baseline, all groups demonstrated a significant increase in bone density, which significantly (p < 0.01) correlated with the number of zoledronic acid administrations. There was increased bone density of at least 100% in 57%, and an increase of at least 50% in 87% of the patients. This increase was significant in both lytic and sclerotic metastases after 3 months of therapy. No significant bone density difference was found in normal-appearing bone. Conclusions Bone density measured by CT increases at metastatic sites after zoledronic acid treatment, regardless of the type of metastasis, in contrast to apparently normal bone.