Added value of 68Ga-PSMA PET/CT for the detection of bone metastases in patients with newly diagnosed prostate cancer and a previous 99mTc bone scintigraphy

PURPOSE: To investigate the added value and diagnostic accuracy of 68Ga-PSMA PET/CT versus bone scintigraphy (BS) for bone metastasis detection at the primary staging of prostate cancer (PCa).

METHODS: Inclusion criteria involved consecutive patients with newly diagnosed intermediate- to high-risk PCa, who had undergone BS, mostly with supplementary SPECT/low-dose CT, and 68Ga-PSMA-11 PET/CT within less than 3 months without therapy initiation between the two investigations. BS was evaluated according to clinical routine and reported as no bone metastases (M0), bone metastases (M1), or equivocal (Me). The 68Ga-PSMA-11 PET/CT was blindly evaluated by three specialists as M0, M1, or Me at the patient level. Sensitivity analyses were conducted using a "best valuable comparator" using all available imaging and clinical follow-up as a reference.

RESULTS: In total, 112 patients were included; 68Ga-PSMA-11 PET/CT showed a sensitivity of 1.00, specificity of 0.93-0.96, positive predictive value of 0.74-0.81, and negative predictive value of 1.00. 68Ga-PSMA-11 PET/CT revealed bone metastases in 8 of 81 patients with M0 disease according to BS. 68Ga-PSMA-11 PET/CT confirmed the presence of bone metastases in all patients (n = 9) with M1 disease according to BS. In patients with Me by BS, 68Ga-PSMA PET/CT provided a definite result in 20 of 22 patients. 68Ga-PSMA-11 PET/CT resulted in a false-positive answer in four patients with solitary rib lesions.

CONCLUSION: 68Ga-PSMA-11 PET/CT revealed bone metastases in 10% of patients without bone metastases on BS and in 36% patients with indeterminate BS. However, solitary PSMA-avid lesions in the ribs should be interpreted cautiously as they may represent false-positive findings.