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Evaluation of Practical Interpretation Hurdles in 68Ga-PSMA PET/CT in 55 Patients

Physiological Tracer Distribution and Incidental Tracer Uptake

Kirchner, Julian, MD*; Schaarschmidt, Benedikt Michael, MD*; Sawicki, Lino Morris, MD*; Heusch, Philipp, MD, PhD*; Hautzel, Hubertus, MD, PhD; Ermert, Johannes, PhD; Rabenalt, Robert, MD§; Antoch, Gerald, MD, PhD*; Buchbender, Christian, MD, PhD*

doi: 10.1097/RLU.0000000000001672
Original Articles
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Purpose To investigate the physiologic 68Ga-PSMA distribution and evaluate focal or diffuse radiotracer uptake in nonprostate cancer malignancies and in incidental findings.

Methods 68Ga-PSMA PET/CT scans in 55 men performed for prostate cancer (49) or renal cell carcinoma (6) staging were analyzed retrospectively. Two radiologists evaluated the datasets in 2 reading sessions. First, physiological 68Ga-PSMA uptake was evaluated. Second, scans were analyzed for incidental uptake. SUVmax and SUVmean were recorded. Other imaging modalities, histopathology, or clinical follow-up served as standard of reference.

Results Homogenous 68Ga-PSMA uptake of the lacrimal glands (SUVmax, 15.7 ± 7.2), parotid glands (SUVmax, 24.4 ± 8.1), submandibular glands (SUVmax, 26.7 ± 7.1), vocal cords (SUVmax, 8.4 ± 3), Waldeyer ring (SUVmax, 10.4 ± 4.3), liver (SUVmax, 8.2 ± 2.5), spleen (SUVmax, 10.9 ± 3.9), kidneys (SUVmax, 66.4 ± 25.4), and pars descendens duodeni (SUVmax, 17.6 ± 8.9) was observed in all patients. In 65% and 36%, respectively, homogenous 68Ga-PSMA uptake of the colon descendens (SUVmax, 10.6 ± 9.2) and the rectum (SUVmax, 3.7 ± 1.1) was found. Approximately 22% exhibited a 68Ga-PSMA uptake of the thyroid (SUVmax, 4.5 ± 1.2), and 21% exhibited a 68Ga-PSMA uptake of the knee’s synovia (SUVmax, 2.9 ± 0.2). Furthermore, 68Ga-PSMA uptake was found in 1 patient because of fibrous dysplasia of the right os ilium (SUVmax, 7.7).

Conclusions Physiologic distribution of 68Ga-PSMA comprises uptake in lacrimal and salivary glands, vocal cords, Waldeyer ring, liver, spleen, and kidneys as well as various parts of the intestine. Moreover, nonspecific tracer uptake is regularly found in the thyroid and the synovia of the knee. 68Ga-PSMA uptake">Incidental 68Ga-PSMA uptake can occasionally reveal nonprostate cancer–associated remodeling processes, such as fibrous dysplasia.

From the Departments of *Diagnostic and Interventional Radiology, and †Nuclear Medicine, University Dusseldorf, Medical Faculty, Dusseldorf; ‡Institute of Neuroscience and Medicine, INM-5: Nuclear Chemistry, Juelich Research Center, Juelich; and §Department of Urology, University Dusseldorf, Medical Faculty, Dusseldorf, Germany.

Received for publication November 8, 2016; revision accepted March 4, 2017.

Conflicts of interest and sources of funding: none declared.

Correspondence to: Benedikt Michael Schaarschmidt, MD, University Dusseldorf, Medical Faculty, Department of Diagnostic and Interventional Radiology, Moorenstrasse 5, D-40225 Dusseldorf, Germany. E-mail: Benedikt.Schaarschmidt@med.uni-duesseldorf.de.

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