^99mTc-prostate-specific membrane antigen single-photon emission computed tomography/computed tomography, an evaluation of the method including comparison with methylene diphosphonate single-photon emission computed tomography/computed tomography

When PSMA-PET/CT and whole-body MRI are not available, current guidelines recommend CT imaging plus bone scan for prostate cancer staging of nodal and distant metastasis. Although ^99mTc-PSMA SPECT/CT (PSMA-SPECT/CT) is thought to be a valuable alternative, its method is not standardized, yet. Methods: In 67 patients PSMA SPECT/CT using 512 to 757 MBq ^99mTc-PSMA-API and MDP-SPECT/CT using 502 to 566 MBq of ^99mTc-MDP were performed. Routinely PSMA SPECT/CT includes whole-body scan after 1 hour and SPECT/CT after 4 to 6 hours. In three patients, repetitive SPECT/CTs were performed between 1 and 6 hours. In PSMA SPECT/CT, variation of administered activity showed no significantly different changes in SUVlbm (SUV). Target-to background ratio (T/B) was higher in lymph nodes than bone lesions. T/B increased over time from 1 to 6 hours. PSMA SPECT/CT detected more lesions than whole-body scan, especially in body trunk. In extremities, no lesions were missed. PSMA SPECT/CT showed significantly higher T/B than MDP SPECT/CT. Mean effective doses were 7, 8 mSv for PSMA SPECT/CT, 5, 1 mSv for MDP SPECT/CT and usually 15 mSv for diagnostic CT. In PSMA SPECT/CT contrast was high and steadily increased within six hours after administration. With respect to patient comfort, imaging after 3 to 5 hours is optimal. Whole-body scan with SPECT/CT of body trunk facilitates detection of smallest lesions in body trunk without missing metastasis in extremities. PSMA SPECT/CT is favored against bone scan plus CT concerning radiation exposure, patient comfort and contrast in bone and lymph node metastases. (author)