Quantitative bone SPECT/CT: high specificity for identification of prostate cancer bone metastases

Purpose: Bone scintigraphy with ^99mTc-labeled diphosphonates can identify prostate cancer bone metastases with high sensitivity, but relatively low specificity, because benign conditions such as osteoarthritis can also trigger osteoblastic reactions. We aimed to investigate the diagnostic performance of ^99mTc-2,3-dicarboxy propane-1,1-diphosphonate (^99mTc-DPD) uptake quantification by single-photon emission computed tomography coupled with computed tomography (SPECT/CT) for distinguishing prostate cancer bone metastases from spinal and pelvic osteoarthritic lesions.

Methods: We retrospectively assessed 26 bone scans from 26 patients with known prostate cancer bone metastases and 13 control patients with benign spinal and pelvic osteoarthritic changes without known neoplastic disease. Quantitative SPECT/CT (xSPECT, Siemens Symbia Intevo, Erlangen, Germany) was performed and standardized uptake values (SUVs) were quantified with measurements of SUV_max and SUV_mean (g/mL) in all bone metastases for the prostate cancer group and in spinal and pelvic osteoarthritic changes for the control group. We used receiver operating characteristics (ROC) curves to determine the optimum SUV_max cutoff value to distinguish between bone metastases and benign spinal and pelvic lesions.

Results: In total, 264 prostate cancer bone metastases were analyzed, showing a mean SUV_max and SUV_mean of 34.6 ± 24.6 and 20.8 ± 14.7 g/mL, respectively. In 24 spinal and pelvic osteoarthritic lesions, mean SUV_max and SUV_mean were 14.2 ± 3.8 and 8.9 ± 2.2 g/mL, respectively. SUV_max and SUV_mean were both significantly different between the bone metastases and osteoarthritic groups (p ≤ 0.0001). Using a SUV_max cutoff of 19.5 g/mL for prostate cancer bone metastases in the spine and pelvis, sensitivity, specificity, positive and negative predictive values were 87, 92, 99 and 49%, respectively.

Conclusion: This study showed significant differences in quantitative ^99mTc-DPD uptake on bone SPECT/CT between prostate cancer bone metastases and spinal and pelvic osteoarthritic changes, with higher SUV_max and SUV_mean in metastases. Using a SUV_max cutoff of 19.5 g/mL, high specificity and positive predictive value for metastases identification in the spine and pelvis were found, thus increasing accuracy of bone scintigraphy.