Intra-individual comparison of Tc-99m-MDP bone scan and the PSMA-ligand Tc-99m-MIP-1427 in patients with osseous metastasized prostate cancer.

To evaluate the detection rate of bone metastases obtained with the PSMA targeting tracer 99mTc-MIP-1427 as opposed to the conventional bone scan with 99mTc-MDP in a collective of advanced stage patients with known osseous metastasized prostate cancer. Methods: 21 Patients with known metastatic disease were staged with both, conventional bone scan and PSMA-ligand scintigraphy, within a time-frame of <10 days. Imaging included planar whole-body scans and SPECT or SPECT/CT with two bed positions 3 h after injection of either 500-750 MBq 99mTc-MIP-1427 or 600-750 MBq 99mTc-MDP. Lesions were scored: typical tumor, equivocal (benign/malignant), or normal within a standard reporting schema divided into defined anatomical regions. Blind and consensus reads were performed with sequential un-blinding: first planar scans, then SPECT/CT, then best valuable comparator including MRI, PET/CT and follow-up exams. Results: 11 patients had PSMA-positive visceral metastases which were predictably not diagnosed with conventional bone scan. However, SPECT/CT was required to distinguish between soft tissue uptake and overlapping bone. 4 patients had extensive MDP negative bone marrow lesions. 7 patients had superscan character in bone scan; in contrast, extent of red marrow involvement was more evident by PSMA-scan. Only 3 patients had completely equal results in the bone-scan and PSMA-scan. Also more suspicious lesions were detected in 16 patients using PSMA-scan in comparison to bone-scan. In two patients (about 10 %) a PSMA-negative tumor phenotype was present. Conclusion: PSMA-scanning presented a clearly advantage versus bone-scans by reducing the number of equivocal findings, in most patients. SPECT/CT is pivotal to differentiate between benign (e.g. degenerative changes), bone metastases and extra-osseous tumor lesions.