PROSTAT KANSERİ TANI VE EVRELEMESİNDE Ga-68 PSMA PET/BT’NİN KATKISI
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Prostate cancer is a curable cancer affecting a significant portion of the male population worldwide. With early diagnosis and curative treatment, a long term survival can be achieved. Imaging and clinical and laboratory findings are essential for diagnosing and distinguishing clinically significant cancer from non- clinically significant cancer, which is vital for an appropriate treatment plan. Clinical studies have proved the superiority of Ga-68 PSMA PET/CT in staging distant metastases, and current studies are very promising for use in diagnosis and local staging. Our study compared the diagnostic value of Ga-68 PSMA PET/CT and mpMRI in patients with intermediate and high-risk prostate cancer. We also aimed to investigate the performance of PSMA PET/CT for distinguishing clinically significant tumors from non-clinically significant ones and to demonstrate its usefulness in predicting tumor aggressiveness. In our study, we performed Ga-68 PSMA PET/CT early whole body and late pelvic imaging in patients diagnosed with prostate cancer who had undergone mpMRI. All patients were treated with radical prostatectomy. We compared both imaging methods based on the gold standard radical prostatectomy. We performed immunohistochemistry (IHC) PSMA staining in index tumors for each patient in tissue samples derived from radical prostatectomy specimens and non- dominant tumors if lesions were suitable. After that, we compared PSMA staining intensity with PSMA PET/CT imaging for each tumor foci. In our study, the true index lesion detection rate was 85% with Ga-68 PSMA PET/CT and 92% with mpMRI. Results were better when PSMA PET/CT and mpMRI were combined (94%). We observed that both imaging modalities have detected clinically significant lesions that others didn’t. PSMA PET/CT was found to be superior to mpMRI in detecting tumor extent, bilateral tumor presence and additional lesions in the prostate gland, in accordance with the literature. Although the number of patients for subgroup analysis was small, PSMA PET/CT effectively distinguished ISUP 1 and 2 tumors. For investigating the presence of extraprostatic extension and seminal vesicle invasion from PSMA PET/CT images, we chose the upper threshold values of the PET image window as tumor SUVmax value and SUVmax15 value to standardize PSMA PET image evaluation. Diagnostic accuracy with both EPU and SVI window values was higher than mpMRI. The diagnostic accuracy of PSMA PET/CT was higher than mpMRI in detecting extraprostatic extension (71.1% and 51.9%, respectively) and seminal vesicle invasion (86.5% and 82.7%, respectively). PSMA PET/CT’s sensitivity was higher in lymph node staging (83.3% vs 60%). In addition, we measured the tumor-capsule interface to determine a cut-off value for the presence of EPU. For the tumour-capsule interface >10.5 mm at the SUVmax15 window, the sensitivity was 85%, and the specificity was 56%. In multivariate logistic regression analyses, the best EPU predictors were the tumor-capsule interface at the SUVmax15 window and the PI-RADS score. The best predictor for SVI was MSKCC-SVI risk percentage. Moreover, parameters representing tumor volume and extent (TL-PSMA, TV, tumor involved segment number) in PSMA PET/CT imaging were associated with locally advanced disease. In PSMA PET/CT, late pelvic imaging detected more lesions, which couldn’t be detected in early whole-body imaging due to decreased background activity(p=0.002). Moreover, the diagnostic accuracy of the tests performed for detecting locally advanced disease was higher (diagnostic accuracy of PSMA PET/CT and mpMRG for EPU 71.1% vs 551.9%; for SVI 86.5% vs 82.9%). SUVmax was positively correlated with the percentage of PSMA 3+ area (rs=0.52, n:54, p<0.001) and H score (rs=0.46, n:54, p<0.001); and negatively correlated with the percentage of low staining areas (rs= -0.37, n:54, p:0.01). SUVmax was positively correlated with the ISUP score (rs=0.43, n<.56, p<0.001). Similar results were found in PSMA IHC staining 3+ area percentage (rs=0.42, n:54, p<0.01). The causes of false negative results in PSMA PET/CT were determined as low ISUP grade (≤2), tumor size, crescent or serpiginous shape, and excessive PSMA negative area in IHC. In conclusion, PSMA PET/CT is an effective imaging modality for detecting primary lesions and distinguishing clinically important tumours in patients with intermediate- high-risk prostate cancer. PSMA PET/CT was superior to mpMRI in detecting tumor extent and volume, additional lesions, extraprostatic extension and seminal vesicle invasion as local staging with a probability of impacting treatment decision. PSMA expression in both PSMA PET/CT and IHC correlates with ISUP grade and tumor aggressiveness. Late pelvic imaging is particularly helpful in patients whose lesions cannot be detected on early imaging. It’s necessary to validate our results in larger cohorts, which include all risk groups.