Optimal time-point for 68 Ga-PSMA-11 PET/CT imaging in assessment of prostate cancer: feasibility of sterile cold-kit tracer preparation?

Abstract

Purpose

In this prospective study, we evaluated the optimal time-point for ⁶⁸Ga-PSMA-11 PET/CT acquisition in the assessment of prostate cancer. We also examined, for the first time the feasibility of tracer production using a PSMA-11 sterile cold-kit in the clinical workflow of PET/CT centres.

Methods

Fifty prostate cancer patients (25 staging, 25 biochemical recurrence) were enrolled in this study. All patients received an intravenous dose of 2.0 MBq/kg body weight ⁶⁸Ga-PSMA-11 prepared using a sterile cold kit (ANMI SA, Liege, Belgium), followed by an early (20 min after injection) semi-whole-body PET/CT scan and a standard-delay (100 min after injection) abdominopelvic PET/CT scan. The detection rates with ⁶⁸Ga-PSMA-11 were compared between the two acquisitions. The pattern of physiological background activity and tumour to background ratio were also analysed.

Results

The total preparation time was reduced to 5 min using the PSMA-11 sterile cold kit, which improved the final radionuclide activity by about 30% per single ⁶⁸Ge/⁶⁸Ga generator elution. Overall, 158 pathological lesions were analysed in 45 patients (90%) suggestive of malignancy on both (early and standard-delay) ⁶⁸Ga-PSMA PET/CT images. There was a significant (p < 0.001) increase in SUVmax on delayed images in suspicious prostates (11.6 ± 8.2 to 14.8 ± 1.0) and lymph nodes (LNs; 9.7 ± 5.9 to 12.3 ± 8.8), while bone lesions showed no significant increase (8.5 ± 5.6 to 9.2 ± 7.0, p = 0.188). However, the SUVmax of suspicious lesions on early images was adequate to support the criteria for correct interpretation (mean SUVmax 9.83 ± 6.7).In 26 of 157 lesions, but a decrease in SUV was seen, mostly in subcentimetre lesions in patients with multiple metastases. However, it did not affect the staging of the disease or patient management. The tumour to background ratio of primary prostate lesions and LNs showed a significant (p < 0.001) increase from the early to the standard-delay acquisition, but no significant increase was seen in bony lesions (p = 0.11).

Conclusion

The PSMA-11 sterile cold kit seems to be feasible for use in routine clinical practice, and it has a shorter radionuclide preparation time and is less operator-dependent than the synthesizer-based production method. In addition, early ⁶⁸Ga-PSMA-11 PET/CT imaging seems to provide a detection rate comparable with that of standard-delay imaging. Furthermore, the shorter preparation time using the ⁶⁸Ga-PSMA-11 sterile cold kit and promising value of early PET/CT scanning could allow tailoring of imaging protocols which may reduce the costs and improve the time efficiency in PET/CT centres.

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