Automated synthesis module and sterile cold kit for ⁶⁸Ga-PSMA-11 do not show differences in PET/CT image quality

Abstract

Introduction: ⁶⁸Ga-labeled urea-based inhibitors of the prostate-specific membrane antigen (PSMA), such as ⁶⁸Ga-PSMA-11, are promising small molecules for targeting prostate cancer (PCa). Although this radiopharmaceutical was mostly produced by the means of automated synthesis modules, a sterile cold kit was recently introduced. The aim of our study was to evaluate the image quality of ⁶⁸Ga-PSMA-11 PET/CT (PSMA-PET) in a population of PCa patients following the injection of comparable activities of ⁶⁸Ga-PSMA-11 obtained with the two different synthetic procedures. A secondary aim was to identify secondary factors which may have an impact on image quality and thus final interpretation. Material and Methods: Two different groups of 100 consecutive PCa patients who underwent PSMA-PET were included in the study. The first group of patients was imaged with ⁶⁸Ga-PSMA-11 obtained by employing synthesis modules while the second group’s tracer activity was synthesized using a ANMI sterile cold kit. All PET images were independently reviewed by two experienced nuclear medicine diagnosticians with at least 2 years of experience in PSMA-based imaging and unaware of the patients' clinical history. The 2 reviewers independently rated the quality of each PSMA-PET scan using a 3-point Likert-type scale. Performance was evaluated on the basis of the expected bio distribution, lesion detection rate and expected physiologic background uptake. Results: Overall, 104/200 (52%) PSMA-PET resulted positive in terms of PCa-related findings. No significant differences in image quality between cold kits and synthesis modules were found (P = 0.176) although a higher proportion of images were rated as "excellent" by the observers among kit examinations when compared to modules (35% vs. 26%). Furthermore, according to multivariate regression analysis, a higher patient age (OR=1.49; CI 95%=1.09-2.02; p<0.05), patient weight (OR=1.68; CI 95%=1.38-2.05; p<0.05) and longer ⁶⁸Ga-PSMA-11 uptake times (OR=1.38; CI 95%=1.11-1.71; p<0.05) were significantly associated with a "not excellent" image quality. Conclusion: No significant differences were identified between the 2 groups of patients undergoing PSMA-PET, therefore we were not able to ascertain any significant influences of tracer production methodology on final scan quality. However, patient age, patient weight and ⁶⁸Ga-PSMA-11 uptake times were significantly associated with an overall poorer image quality.