direct comparison of 99mtc-psma spect/ct and 68ga-psma pet/ct in patients with prostate cancer

Objective(s): 99mtc-psma spect/ct is a cost effective alternative for 68ga-psma pet/ct. the aim of this study was to directly compare these two techniques in patients with prostate cancer. methods: 28 man with prostate cancer were studied using 99mtc-psma spect/ct and 68ga-psma pet/ct in a short time period (<60 days). no intervention was done between the studies. whole body pet/ct was done 60 minutes after iv injection of 2 mbq/kg of 68ga-psma. 99mtc-psma kit (psma i+s) was used for spect/ct and whole body imaging was performed 4 hours after iv injection of 740 mbq of 99mtc-psma. images were interpreted independently and the results of each imaging were recorded. results: the mean age of the patients was 64.7±9.6 years old and the mean time difference between two sets of images was 16.6±13.5 days. abnormal uptake was seen in 25 (89.2%) patients by 68ga-psma pet/ct and 20 (71.4%) patients with 99mtc-psma spect/ct. no patients with positive 99mtc-psma spect/ct had negative 68ga-psma pet/ct. the mean number of detected lesions was 26.07±27.5 by 68ga-psma pet/ct and 10.52±10.99 by 99mtc-psma spect/ct (p<0.001). detection of lymph nodes and bone metastases were not significantly different between two sets of imaging (p>0.05), however 68ga-psma pet/ct were more successful in detection of prostate bed lesions compared to 99mtc-psma scan. interestingly, no patient with psa level of >2.1 ng/ml had discordant result between two sets of images. conclusion: 99mtc-psma spect/ct is as accurate as 68ga-psma pet/ct in m staging, however 68ga-psma pet/ct detected more lesions compared to 99mtc-psma spect/ct. detection rate was not significantly different between two techniques in patients with psa levels>2.1 ng/ml.