Optimal time-point for68Ga-PSMA-11 PET/CT imaging in assessment of prostate cancer: feasibility of sterile cold-kit tracer preparation?

In this prospective study, we evaluated the optimal time-point for68Ga-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.

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 weight68Ga-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 with68Ga-PSMA-11 were compared between the two acquisitions. The pattern of physiological background activity and tumour to background ratio were also analysed.

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 single68Ge/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).

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, early68Ga-PSMA-11 PET/CT imaging seems to provide a detection rate comparable with that of standard-delay imaging. Furthermore, the shorter preparation time using the68Ga-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.

European journal of nuclear medicine and molecular imaging. 2018 Feb 23 [Epub ahead of print]

Mohsen Beheshti, Zeinab Paymani, Joana Brilhante, Hans Geinitz, Daniela Gehring, Thomas Leopoldseder, Ludovic Wouters, Christian Pirich, Wolfgang Loidl, Werner Langsteger

Department of Nuclear Medicine & Endocrinology, PET-CT Center LINZ, Ordensklinikum, St. Vincent's Hospital, Seilerstaette 4, A-4020, Linz, Austria. ., Department of Nuclear Medicine & Endocrinology, PET-CT Center LINZ, Ordensklinikum, St. Vincent's Hospital, Seilerstaette 4, A-4020, Linz, Austria., Department of Radiation Oncology, Ordensklinikum, St. Vincent's Hospital, Linz, Austria., ANMI SA, Liege, Belgium., Department of Nuclear Medicine & Endocrinology, Paracelsus Medical University, Salzburg, Austria., Department of Urology, Prostate Cancer Center, Ordensklinikum, St. Vincent's Hospital, Linz, Austria.

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