Abstract
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Introduction: Patients with prostate cancer can be stratified into high and low risk on the basis of prostate specific antigen (PSA) levels, Gleason score at biopsy and clinical stage. High risk PCa needs skeletal evaluation for detection of distant metastasis, widely used method being bone scan. Limitations of the bone scan has brought 18F- FluoridePET/CT to the forefront which is highly sensitive. PET/CT with Ga68-labeled PSMA inhibitor has been shown to be of high clinical value for lymph node staging and is emerging as the imaging modality of choice for PCa staging.
Aim: The purpose of this study was to compare the diagnostic performance of Ga68-PSMA PET/CT and F18-NaF PET/CT, in detection of skeletal metastasis, in a prospective cohort of patients with high risk prostate cancer (PCa). Materials and Methods: Forty patients biopsy proven PCa with mean age of 64.42years(+/-8.83) were recruited in the period between June 2017 to June 2018. All the patients were high risk PCa patients with a mean PSA:55.48(+/-56.00) and Gleason score 7. The participants underwent two scans within 30 days. PET/CT was performed 60 minutes after injecting 370-550MBq F18 NaF intravenously and after 60 minutes of injection of 74-185MBq Ga68-PSMA . Each scans were evaluated independently by two blinded Nuclear Medicine physicians qualitatively and quantitatively.
Results: Of the 40 patients,18 patients(45%) showed no skeletal metastasis in both the scans. Of these 12/18 (66.67 %) had lymph nodal lesions in Ga68-PSMA PET/CT. Skeletal lesions were detected by both the modality in 16 (40% )patients with median PSA of 43.10, and 9/16 patients had lymph node involvement. In 6/40 patients, F18 NaF PET/CT alone detected skeletal metastasis at a lower median PSA of 27.0ng/ml, with lymph nodal positivity of 5/6 (83.33%). Total number of lesions detected by F18 NaF and Ga68-PSMA were 165 and 187.NaF detected more lesions than PSMA PET in 12 instances at lower median PSA 29.79, compared to Ga68-PSMA detecting more lesions only in 4 instances (median PSA 140.25).Thus, NaF PET/CT had higher detection rates of skeletal lesions at lower PSA. Sperman correlation between number of lesions and PSA was found to be 0.411(p=0.057) in NaF PET/CT and 0.430(p=0.096) in PSMA PET/CT, both showing moderate positive correlation, which would have been statistically significant if more patients were included. Mean and median SUV max of Fluoride lesions were more than PSMA (53.91 vs 28.33,p <0.001) aiding in easier visual identification. No correlation was found between the SUV max of both tracers in concordant lesions. No statistical difference was found between the age and Gleason score of the patients with positive and negative lesions in both the scans. However for both PSMA (lesion positive: PSA 43.10 vs negative 28.71; p= 0.090) and fluoride (lesion positive: PSA 34.66 vs negative 29.14; p=0.240), skeletal lesions were positive at higher median PSA.
Conclusions: Compared to Ga68-PSMA PET/CT , F18 NaF PET/CT detected more skeletal lesions and at lower PSA values, with number of detected lesions per patient showing a moderate positive correlation in both.