Dr Iain Duncan
An update December 2019

We started doing Tc-PSMA SPECT/CT scans at GMI in 2016 and have now done about 300. Initially there was a steep learning curve as we worked on improving the technical parameters and image reconstruction, but over time I have become confident that we are producing a high quality clinically important scan.

I have recently reviewed our data and am pleased to note that the scan quality and more importantly the scan results are close to the benchmarks defined by the  world literature on Ga-PSMA PET scans. Our detection rates are higher than the limited publications on Tc-PSMA. Our detection rate for recurrent disease post prostatectomy is shown in the table below.

 

PSA (ng/ml) Number +SCAN -SCAN
<0.5 39 23 (59%) 16 (41%)
0.5-1.0 15 11 (73%) 4 (27%)
1.0-5.0 51 45 (88%) 6 (12%)
>5 133 130 (98%) 3 (2%)

Table 1: Detection rates for recurrent disease Tc-PSMA at GMI 2016-19.

We also had 108 cases in which we had a comparative MRI at staging of the primary disease. As suggested in the literature for Gallium PSMA we found more disease in the prostate than the MRI in a substantial number of cases (table 2 below).

MRI v PSMA in prostate Number %
Discordant 3 3.5%
Concordant 36 46%
More disease on PSMA 37 47%
Less disease on PSMA 3 3.5%

Table 2: Comparison of mpMRI with Tc-PSMA for carcinoma of the prostate

In 236 cases we had enough data to compare Tc-PSMA with conventional staging (CT scan +-Bone scan). In 145 cases (61%) there was no change. In the remaining 39% staging was altered: 15% upstaged; 13.6% different disease distribution; and 10% down-staged.

We also had enough data to compare serum PSA, Gleason score at pathology, and SUVmax (PSMA uptake) of the principal prostate lesion in 146 cases (Figure 2). This shows a stronger correlation between SUVmax and Gleason score than between PSA and Gleason score (poor correlation).

Figure 2: PSA and SUVmax (Y axis) and Gleason Score (X axis).