Opportunistic screening for osteoporosis with CT performed before dose planning for radiation therapy

Abstract

Purpose: Radiotherapy can negatively impact bone health, affecting the activity of osteoblasts, osteoclasts, and osteocytes, leading to dysfunction in bone remodeling and reduced bone mineral density (BMD). This increases the risk of fractures in irradiated bone. Preexisting osteoporosis is a well-known risk factor of radiotherapy induced fractures. While Dual energy X-ray Absorptiometry (DXA) is the gold standard for diagnosing osteoporosis, it is not routinely performed before radiation therapy. This study aimed to develop and validate a method for opportunistic screening for osteoporosis by estimating the bone mineral density from computed tomography (CT) scans used for radiation treatment planning. The study also sought to categorize patients into low, moderate, or high risk for osteoporosis. Method: A total of 179 women (mean age 67.8 ± 8.6, range 35-85 years) treated for adjuvant breast cancer were included in the study. Of these, 101 patients underwent both DXA and CT scans within a four-month period. A spherical volume of interest (VOI) was used to extract HU values from the trabecular region of Th4-L1. BMD was estimated using two methods: a translation curve derived from known calcium content and HU values for fourteen reference bone tissues, and internal calibration. Eight additional patients treated for gynecological cancer were included to study how BMD varied in the spine and to develop thoracic BMD cutoff values. Validation was performed using a European Spine Phantom (ESP). Results: A translation curve from HU values to BMD was derived as BMD = 0.7161 · HU − 1.212. Using this equation, BMD estimates in the ESP showed good agreement with actual values. Thoracic BMD cutoff values for osteopenia and osteoporosis were derived as 91 mg/cm3 and 124 mg/cm3, respectively. A moderate correlation was found between BMD estimated using DXA, areal BMD (aBMD), and CT based BMD (r=0.51, p<0.001). The CT-based method detected more cases with low BMD compared to DXA. Conclusion: CT images acquired for radiotherapy planning can be used to assess BMD, with good agreement to phantom measurements and higher sensitivity compared to DXA. Further research is needed to evaluate the method at different anatomical sites and validate thresholds for low bone density. Future research should also identify and quantify the uncertainties related to the method.