Use of micro-positron emission tomography with (18)F-fallypride to measure the levels of dopamine receptor-D2 and (18)F-FDG as molecular imaging tracer in the pituitary glands and prolactinomas of Fischer-344 rats

18F-fallypride and 11C-methionine positron emission tomography/computed tomography for the study of prolactinomas and nonfunctioning pituitary adenomas: A case series

Some studies have assessed the expression of dopaminergic dopamine 2 (D2)/3 receptors in prolactinomas and nonfunctioning pituitary adenomas (NFPA) by positron emission tomography/computed tomography (PET/CT) with ¹¹C-raclopride, proving that this modality can be useful to predict the response to treatment with dopamine agonists. However, the use of ¹¹C-labeled radiotracers is limited, as it requires a cyclotron in the PET center. ¹⁸F-fallypride is a radiotracer that has proven useful in assessing the expression of D2/3 receptors. As it is labeled with ¹⁸F, it can be produced and transported to distant PET centers. There are no studies on the usefulness of ¹⁸F-fallypride for the evaluation of patients with prolactinomas and NFPA. The aim of this study was to describe the first case series of patients with prolactinomas and NFPA studied with ¹⁸F-fallypride and ¹¹C-methionine PET/CT to reveal D2/3 expression and amino acid (AA) metabolism. ¹⁸F-fallypride and ¹¹C-methionine uptake were assessed in a case series of six patients, five with prolactinomas and one with a NFPA, and compared with clinical presentation and follow-up at 6–18 months. All patients presented with macroadenomas, with a wide range of AA metabolism, as revealed by ¹¹C-methionine PET/CT. ¹⁸F-fallypride PET/CT identified low to moderate/high D2/3 expression in the tumors. The patient that presented low expression of D2/3 in the tumor and high AA metabolism showed a poor response to DA therapy. ¹⁸F-fallypride was able to reveal D2/3 receptor expression in prolactinomas and NFPA, with the advantage of been a more accessible radiotracer in comparison with previous ¹¹C labeled analogs.