Physiological biodistribution on Ga68-PSMA PET/CT and the factors effecting biodistribution.

AIM: The study aims to determine the physiological and pathophysiological distribution of the radiopharmaceutical (Ga68-PSMA-617) and investigate whether there are differences in distribution according to the laboratory, histopathological and clinical findings that can affect image evaluation. Also, we aimed to determine cut-off values to distinguish physiological and pathological uptake in prostate, bone, and lymph nodes. MATERIALS AND METHODS: 229 prostate cancer patients who underwent Ga68-PSMA PET/CT at our department were retrospectively analyzed. The patients were grouped according to PET/CT results, Gleason scores, PSA values, received treatments, metastatic status and other laboratory values. The SUV values of the organs, tissues, and pathological lesions of the patients in these subgroups were compared among themselves. RESULTS: No significant difference was detected in the physiological uptake of lymph nodes and bone between the groups. In the group with patients that received androgen deprivation therapy (ADT), the bone metastasis SUV values were found to be higher and the SUV values of the submandibular gland and renal cortex were found to be lower (Mann-Whitney U, p = 0.043; 0.004; 0.01, respectively). In the group with patients who received radiotherapy, the normal prostate tissue SUV values were determined to be higher (Mann-Whitney U, p = 0.009). The SUV values of the submandibular gland, muscle, liver, and blood pool were found to be lower in the group of patients with high serum LDH values. The cut-off SUVmax value was determined to be 6.945 (sensitivity 89.6%, specificity 98.1%) for primary prostate lesion; 4.72 for lymph node metastasis; 4.25 for bone metastasis. The serum PSA cut-off value to distinguish the negative/positive groups was found to be 1,505 (sensitivity 79.7%, specificity 77.3%). CONCLUSION: In conclusion, PSMA-617 demonstrates a similar biodistribution with other PSMA ligands. The physiological uptake of lymph nodes and bone which are mostly metastasized in prostate cancer, are not affected by the factors we examined. It should be kept in mind that the normal prostate tissue uptake may increase in patients receiving radiotherapy, and the physiological/pathological uptake of the organs may differ due to the changes in PSMA expression in patients receiving ADT, tumor burden, and kidney function may affect the biodistribution.

Neurolymphomatosis with Spinal Nerve Root Involvement Demonstrated on 18F-FDG PET/CT.

A 56 years old woman with a diagnosis of diffuse large B-cell lymphoma had dyspnea, weakness in the left upper extremity and vocal cord paralysis after chemotherapy. She underwent cervical, thoracal and lumbosacral magnetic resonance imaging (MRI) however findings on MRI could not entirely explain the symptoms of the patient. Therefore, the patient underwent 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography and the scan revealed focal symmetrical 18F-FDG uptake on the cervical, thoracal and lumbal spinal nerve roots. Considering the symptoms of the patient and cerebrospinal fluid cytology findings, hypermetabolic spinal nerve roots were interpreted as lymphoma involvement.

FDG PET/CT and Conventional Imaging Methods in Cancer of Unknown Primary: an Approach to Overscanning.

PURPOSE: To compare the performance of fluorine-18 fluorodeoxyglucose positron emission tomography and computed tomography (FDG PET/CT) with conventional imaging methods (CIM), including computed tomography (CT), magnetic resonance imaging (MRI), and mammography (MMG) in cancer of unknown primary (CUP). METHODS: A total of 36 patients with CUP, who referred to our clinic for a FDG PET/CT scan, were enrolled in this study. Thirty of the patients were also examined through either diagnostic CT/MRI and/or MMG. The diagnostic performance of both methods for the primary cancer location was analyzed. The results of FDG PET/CT and CIM were compared based on the standard reference of the histopathology and/or clinical and laboratory follow-up. RESULTS: The primary cancer locations were detected in 24 patients (66.6%, 24/36) by FDG PET/CT, whereas CIM identified the locations in 16 patients (53.3%, 16/30). Sensitivity, specificity, PPV, NPV, and accuracy rates of the detection of the primary tumor localizations were as follows: 83, 70, 89, 58, and 79% for FDG PET/CT; 70, 62, 84, 42, and 68% for CIM, respectively. There was no statistical significance between modalities regarding any of the categories in 30 patients. CONCLUSION: FDG PET/CT detected the primary tumors of the patients with CUP more than CIM did. However, the difference between them was not found to be statistically significant. It may be considered that FDG PET/CT scan can be performed as a first-line tool in the initial diagnosis of the patients with CUP and to add radiodiagnostic imaging in selective cases. We conclude that if the first-line examination of a CUP patient has been already performed by a CIM and the result was negative or inconclusive, FDG PET/CT can be considered to avoid unnecessary imaging procedures.

Tc-99m red blood cell bleeding scan in a pregnant woman presenting with hematemesis: a brief review of indications and guidelines for radionuclide scans during pregnancy.

A 6-month pregnant 35-year-old woman with hematemesis and dark blood in her stool was evaluated for location of an active gastrointestinal bleeding site. The findings from 2 esophagogastroduodenoscopies and a colonoscopy were negative. The patient was referred for a Tc-99m red blood cell scintigraphy, for location of an active bleeding site. As the patient was 6 months pregnant, the necessity of the case was discussed with the patient's referring physician and after determining that this study was necessary, the risk of radiation exposure to the fetus was discussed with the radiation safety officer and the patient. The procedure was performed after the patient signed informed consent regarding the considerations of radiation safety to the fetus. The Tc-99m red blood cell bleeding scan clearly shows activity in the fetus in addition to a large arteriovenous malformation in the patient. The visualized fetus prompted this report to discuss radiation risks concerns and a brief review of indications and guidelines for performing nuclear medicine procedures in pregnant patients.