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

Abstract

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.

Keywords: 99mTc-DPD; Bone metastases; Bone scintigraphy; Prostate cancer; Prostate cancer metastases; Quantitative SPECT; SPECT/CT; SUV; Spinal osteoarthritis; xSPECT.

Fig. 1

a Osteoblastic lesion of the pelvis in a 57-year-old male patient known for prostate cancer, showing a high SUV_max of 28 g/mL and SUV_mean of 17 g/mL. b Lumbar spine osteoarthritic changes of the L4-L5 facet joints in a 83-year-old male patient with hip pain, showing SUV_max of 15 and 13 g/mL and SUV_mean of 9.0 and 7.8 g/mL in the left and right facet joints, respectively

Fig. 2

Box-and-whisker plots of SUV_max overall (a) and depending on metastases location (b)

Fig. 3

Box-and-whisker plots of SUV_max depending on presence or absence of previous systemic therapy in all bone metastases (a) and in spinal and pelvic bone metastases (b)

Fig. 4

ROC curves of SUV_max and SUV_mean for spinal and pelvic prostate cancer bone metastases, with AUCs of 0.947 and 0.943, respectively