Abstract
P816
Introduction: In suspected cases of Prostate cancer, including men presenting with prostatomegaly with lower urinary tract symptoms or abnormal raised serum prostate specific antigen (PSA), the diagnostic method is prostate biopsy. Radiological non-invasive techniques for prostate cancer detection include ultrasonography and multiparametric MRI (mpMRI), the latter known to have better accuracy than the former. 68Ga-PSMA (Prostate Specific Membrane Antigen) is a radiotracer which shows high localization in prostate cancer cells. The aim of this study was to assess the sensitivity and utility of 68Ga-PSMA PET/CT in comparison with mpMRI as a noninvasive imaging technique for the initial diagnosis and locoregional staging of prostate cancer.
Methods: Sixty patients (n=60) with biopsy proven prostate carcinoma were evaluated. They underwent mpMRI including Gadolinium enhanced scans with PIRADS grading. Whole body 68Ga-PSMA PET/CT scans were performed using 1.8-2.2 MBq per kilogram bodyweight of Ga68-PSMA injected intravenously. On 68Ga-PSMA PET/CT, lesions with focal high tracer uptake in prostate gland were considered positive for malignancy using a cut-off maximum standardized uptake value (SUVmax) (gm/bw) of 3.2. 3 hours delayed PET/CT of pelvis was acquired, wherever necessary. On mpMRI, PIRADS 4 and 5 lesions were considered malignant. TRUS biopsy results were divided into lesions in right and left lobes of prostate, and taken as gold standard to compare the findings of the two imaging modalities. T staging of disease, N staging of lymph nodes within the pelvis and M staging of lesions in pelvic bones (within the imaging field of mpMRI) were compared.
Results: All 60 patients showed 68Ga-PSMA avid disease, whereas 55 were detected by mpMRI. The SUVmax of prostate lesions ranged from 3.6 to 101.4. The sensitivity in detection of prostatic lesions (with 95% confidence interval) was 99.08% for 68Ga-PSMA PET/CT and 84.40% for mpMRI. 68Ga-PSMA PET/CT detected additional areas of disease in 3 patients (5%), when compared to TRUS biopsy. Good agreement was found between 68Ga-PSMA PET/CT and mpMRI, for seminal vesicle involvement (κ = 0.777). Neurovascular bundle involvement and extracapsular extension were seen in 25 patients in mpMRI, whereas this could not be commented upon on 68Ga-PSMA PET/CT. 68Ga-PSMA PET/CT detected greater number of patients with regional lymph nodal involvement (19/60) as compared to mpMRI (12/60). Thus 68Ga-PSMA PET/CT upstaged the disease to N1 in 7 patients (11.6%). 68Ga-PSMA PET/CT showed PSMA avid pelvic skeletal lesions in 9 patients, whereas mpMRI detected pelvic lesions in 6 patients. In addition, 4 other patients showed extrapelvic skeletal lesions and 1 patient showed pulmonary metastasis on 68Ga-PSMA PET/CT which were beyond the field of view of MRI.
The correlation between SUVmax of Ga68-PSMA PET/CT and Gleason score, as well as, SUVmax and serum PSA level were found to be statistically significant, p values being 0.003 and 0.001 respectively.
Among 60 patients with prostate cancer, 33 patients had localized disease, whereas locally advanced and metastatic disease were seen in 13 and 14 patients respectively. The mean SUVmax of localized, locally advanced and metastatic groups were found to be 19.54, 20.12 and 24.06 respectively. This was found to be statistically not significant (p value = 0.285).
Conclusions: 68Ga-PSMA PET/CT has superior sensitivity in detection of intraglandular primary prostate tumor, as compared to mpMRI. Both modalities correlate well in detection of seminal vesicle involvement. 68Ga-PSMA PET/CT outperformed mpMRI in detection of lymph nodal and skeletal metastases. Hence, 68Ga-PSMA PET/CT should be considered as a first line diagnostic imaging modality for carcinoma prostate. If 68Ga-PSMA PET/CT shows localized/ locally advanced disease, then mpMRI may be needed only in selected cases for surgical assessment to detect the involvement of neurovascular bundle and extracapsular extension.
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