Remineralization of lytic spinal metastases after radiotherapy

Abstract

BACKGROUND CONTEXTPalliative radiotherapy (RT) can lead to remineralization of osteolytic lesions thereby potentially restoring some of the weight-bearing capacity and preventing vertebral collapse. It is not clear, however, under which circumstances remineralization of osteolytic lesions occurs. PURPOSEThe aim of this study was to investigate the change in bone mineral density in spinal metastases after RT compared to a reference region, and find associated factors. STUDY DESIGNRetrospective analysis within prospective observational cohort OUTCOME MEASURESchange in bone mineral density measured in Hounsfield Units (HU). PATIENT SAMPLEpatients treated with RT for (painful) bone metastases. METHODSPatients with spinal metastases were included if computed tomography scans both pre- and post-RT were available. Bone density was measured in HU. A region of interest (ROI) was drawn manually in the metastatic lesion. As a reference, a measurement of bone density in adjacent, unaffected, and non-irradiated vertebrae was used. Factors tested for association were origin of the primary tumor, RT dose and fractionation scheme, and concomitant use of bisphosphonates. RESULTSA total of 31 patients with 49 spinal metastases, originating from various primary tumors, were included. The median age on baseline was 58 years (IQR: 53–63) and median time between baseline and follow-up scan was 8.2 months (IQR: 3.0–18.4). Difference in HU in the lesion before and after treatment was 146.9 HU (95% CI 68.4–225.4; p<.01). Difference in HU in the reference vertebra between baseline and first follow-up was 19.1 HU (95% CI -47.9 to 86.0; p=.58). Difference between reference vertebrae and metastatic lesions on baseline was -194.1 HU (95% CI -276.2 to -112.0; p<.01). After RT, this difference was reduced to -50.3 HU (95% CI -199.6 to 99.0; p=.52). Patients using bisphosphonates showed a greater increase in HU, 194.1 HU versus 60.6 HU, p=.01. CONCLUSIONSPalliative radiation of osteolytic lytic spinal metastases is positively associated with an increased bone mineral density at follow-up. The use of bisphosphonates was linked to an increased bone mineral density when used during or after RT.