Transitioning to whole-body SPECT/CT in prostate cancer staging: a new concept for a better imaging workflow.

 Whole-body bone scan (BS) is the clinical standard in detecting bone metastases in prostate cancer patients. Additional SPECT/CT has allowed to significantly increase its diagnostic accuracy. However, performing both planar and additional SPECT/CT prolongs the total examination time and lowers patient throughput. In this study we aim to assess the diagnostic performance of a SPECT/CT-only protocol compared to the traditional procedure that is BS with a facultative SPECT/CT in case of unclear findings. 50 patients with high-risk prostate cancer and suspected bone metastases were enrolled in this retrospective study. All patients received a whole-body Tc-99m-DPD BS followed by a 3 field-of-view (FOV) SPECT/CT (GE Discovery 670 Pro) covering an area from the vertex to the mid-femur. Metastatic lesions were evaluated visually on BS and SPECT/CT and correlated to PSA-levels. Detection rate was up to 50 % higher in SPECT/CT than in BS (n = 2829 vs. n = 1942; p < 0.001), but 31/1942 (1.5 %) lesions detected on BS were located out of the SPECT/CT field-of-view. In our analysis a PSA-level of > 80 µg/l could be defined as a cut-off-value for metastatic spread beyond mid-thigh, as no patient with PSA< 80 µg/l had localizations outside the SPECT/CT field-of-view (AUCPSA = 0.95, p < 0.001 sensitivity: 100 %, specificity: 77 %, NPV: 100 %, PPV: 67 %). The SPECT/CT-only protocol did not prolong acquisition time significantly as compared to BS. In patients with high-risk prostate cancer presenting with PSA < 80 µg/l and absent clinical symptoms, vertex to mid-thighs 3-FOV-SPECT/CT was representative for the entire skeletal system and was able to detect more lesions than planar acquisition. This procedure did not prolong patient handling time significantly.