Abstract
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Objectives: 68Ga-PSMA-11 PET is an excellent tool for the evaluation of men with biochemically recurrent prostate cancer. There are reports indicating dual-time imaging may result in identification of more lesions than single-time imaging. The objective of this study was to compare the diagnostic performance of a new PET/CT scanner (Discovery Molecular Insights - DMI) using silicon photomultipliers (SiPM) detectors vs standard LYSO detectors PET/CT (Discovery 690 - D690) in patients with biochemical recurrence following a single injection of radiopharmaceutical.
Methods: Thirty-two patients were prospectively recruited to undergo scans on the D690 and DMI scanners, in randomized order. Images from the D690 were reconstructed using time-of-flight (ToF) and an ordered subset expectation maximization (OSEM) protocol. Images from the DMI were reconstructed using ToF and a Bayesian penalized likelihood algorithm (Q.Clear®). Two experienced readers reviewed both scans for each patient in random order, recorded the number and location of each lesion, and acquired standardized uptake value (SUV) measurements.
Results: Fifteen patients underwent scans on the D690 first followed by the DMI, and 17 underwent scans in the reverse order. Excluding one patient with a very high PSA of 1170 ng/mL, the mean PSA at time of scan was 7.3 ng/mL. PSMA PET detected sites of recurrence in 24/32 (75 %) patients, including 8/12 (66.7%) patients with PSA below 1 ng/mL, and the lowest PSA with a positive scan was 0.21 ng/mL. Although the performance of the two scanners was equivalent on a per-patient basis, the DMI identified four additional sites of metastases. In all these cases the DMI scan was done first, suggesting superior detector technology contributing to results and not delayed imaging. When scanned on the D690 first followed by the DMI, the mean lesion SUVmax increased from 13.5 to 23.5 (p<0.001). When scanned on the DMI first followed by the D690, the mean lesion SUVmax showed little change, increasing from 17.8 to 17.4 (p=0.773).
Conclusions: Delayed imaging did not contribute to detection of additional lesions in this cohort of patients with biochemically recurrent prostate cancer. However, SiPM-based DMI (used for early imaging) identified four additional lesions compared to LYSO-based D690 (used for delayed imaging), likely due to superior detector technology. These results need to be confirmed in larger studies.
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