ABSTRACT

68Ga prostate-specific membrane antigen (PSMA) positron emission tomography/computerized tomography (PET/CT) imaging has been used efficiently in the evaluation of prostate cancer (PCa). There are three kinds of urea-based PSMA ligands labeled with 68Ga, including PSMA 11, PSMA Imaging & Therapy (I&T), and PSMA 617. The aim of the present study was to investigate the in vivo distribution of the novel ligand PSMA I&T in normal tissues and to identify benign variants.

We retrospectively evaluated 34 patients with PCa who underwent 68Ga PSMA I&T PET/ CT imaging in our clinic between August 2017 and December 2017. Only patients who had no evidence of recurrent disease on conventional imaging performed before the 68Ga PSMA I&T PET/ CT scan were included in the study. Patients also had no 68Ga PSMA avid lesion in favor of residual disease or recurrent disease on PET scan. The average age of the patients was 70.2±8.5 years.

Evaluation of the conventional maximum intensity projection images revealed uptake of 68Ga PSMA in the lacrimal, submandibular, and parotid glands; liver; spleen; kidneys; duodenum; jejunum; ileum; and urinary bladder. The radionuclide uptake of the body structures from the highest to the lowest in terms of SUVmax values was listed as kidneys, submandibular and parotid glands, urinary bladder, jejunum-ileum, lacrimal gland, duodenum, spleen, liver, and transverse colon. When SUVmean values are concerned, the list, from the highest to the lowest, was as follows: kidneys, urinary bladder, submandibular and parotid glands, duodenum, lacrimal gland, spleen, jejunum-ileum, liver, and transverse colon. We detected osteophytes in 15 patients, and 8 of them demonstrated mild uptake. We detected mild uptake in the celiac ganglia of 4 patients. We did not observe any physiological uptake in the surrenal glands, but there were two adenomas that show low degree of uptake. When double organs are compared, the SUVmax values of the right lacrimal, sublingual, and parotid glands were higher than those of the left counterparts, and differences were statistically significant (p<0.05), but there was not any statistically significant difference between the right and the left organs when SUVmean values were concerned. The liver showed less uptake, whereas blood pool showed more uptake when the distribution of PSMA I&T is compared with the studies made with the PSMA 11 ligand.

To our knowledge, this is the first study in the literature that aimed to reveal the distribution pattern of 68Ga PSMA I&T. The in vivo distribution of PSMA I&T is almost congruent with the PSMA expression in the tissues defined with immunohistochemical results, and there are minor differences between PSMA 11 and PSMA I&T regarding normal tissue uptake.