Comparison of 68 GA-PSMA PET/CT with pelvic MRI and whole body bone scintigraphy in detecting metastases in prostate cancer

Prostate cancer is the second leading cause of malignant tumors in males worldwide after lung cancer and is still the fifth cause of cancer-specific mortality. It mostly metastasizes to the skeletal system and lymph nodes. Bone scintigraphy is the most commonly used method of screening bone metastases. Pelvic MRI and CT are used to scan lymph node metastases. There is a limited number of studies related to the effectiveness of the 68Ga-PSMA PET/CT, another technique, in detecting bone and lymph node metastases. The aim of this study was to compare between the results of bone scintigraphy with 68Ga-PSMA PET/CT and the results of magnetic resonance imaging of the pelvic region through 68Ga-PSMA PET/CT, in addition, to predict how accurate the pre-treatment staging is, by recording the PSA follow-up and the recurrence of PSA after the diagnosis of the disease stage and treatment. The data of 1200 patients scanned with 68Ga-PSMA PET/CT and histopathologically diagnosed with prostate cancer in the Department of Nuclear Medicine at Akdeniz University Medical Faculty Hospital in 2015-2018 was retrospectively investigated using the hospital data system. The faculty members of the Department of Nuclear Medicine and Radiology at Akdeniz University Medical Faculty Hospital interpreted the findings belonging to the patients. To compare the findings, the patients having 68Ga-PSMA PET/CT and 68Ga-PSMA PET/CT with whole-body bone scintigraphy, and pelvic MRI within a maximum period of 120 days were included in the study. If a new treatment had been started, or the treatment had been changed between the two examinations, the patients were excluded from the study. Seventy patients in the TVKS group and 63 patients in the pelvic MRI group were included in the study after inclusion and exclusion criteria were applied. The minimum 6-month, maximum 48 monthly PSA follow-up and the treatments after diagnosis of these patients were also noted, so we aimed to understand which examination was more effective in predicting metastasis and the rates of false positivity. In predicting bone metastasis, 68Ga-PSMA PET/CT was determined to be ahead of bone scintigraphy. Patients with false positivity in bone scintigraphy were considered to have no bone metastasis, based on the 6-48 monthly PSA follow-up after the given treatments, although not statistically significant, the number of patients with PSA recurrence was only 2 out of 26 patients. In our study, although 68Ga-PSMA PET/CT seemed to be superior to the MRI in predicting bone metastasis, the difference was not statistically significant; we think there are the need for new studies with large case series. In our study, MRI and 68Ga-PSMA PET/CT were compared in terms of detecting lymph node metastases; In the 43 patients, LN were not detected by 68Ga-PSMA PET/CT and MRI; 8 patients also were found to have LN by 68Ga-PSMA PET/CT but not by MRI. The difference was considered statistically significant (P = 0.001). In this study, 68Ga-PSMA PET/CT was seen to be more prominent in predicting lymph node metastases than MR imaging. Consequently, in our study, 68Ga-PSMA PET/CT was superior to bone scintigraphy and pelvic MRI in the evaluation of both bone and lymph node metastases. We believe that using 68Ga-PSMA PET/CT in the staging will be a more accurate choice because the false positivity rates are lower and because screening of the patient with single examination instead of two examinations can provide us with additional information on detecting solid organ metastases except for 68Ga-PSMA PET/CT bone and pelvic lymph node metastasis. Keywords: Prostate cancer, 68Ga-PSMA PET/CT, Whole Body Bone scintigraphy, Pelvic MRI