The Application Of ⁶⁸Ga-PSMA PET/CT On The Diagnosis And Evaluation Of Primary Prostate Cancer

Background:Early diagnosis,accurate clinical staging as well as risk classification of prostate cancer is essential for categorizing the severity of disease,estimating prognosis and recommending proper treatment.Multiparametric magnetic resonance imaging(mpMRI),a commonly used imaging tool,has some limitations on the evaluation of prostate cancer.A novel imaging tool based on prostate specific membrane antigen(68Ga-PSMAPET/CT)has shown great performance on the diagnosis of recurrent prostate cancer.However,the study on its application on the evaluation of primary prostate cancer was very limited.Meanwhile,a few studies have shown that androgen deprivation therapy(ADT)can affect the expression of PSMA and then affect the diagnosis of prostate cancer by 68Ga-PSMAPET/CT.Objectives:This study is intended to explore the application of 68Ga-PSMAPET/CT on primary prostate cancer detection and evaluation as well as the impact of ADT on 68Ga-PSMA PET/CT.The specific research purpose are as follows:1)to explore whether the combination of 68Ga-PSMA PET/CT and mpMRI could improve the detection of clinically significant prostate cancer(csPCa);2)to explore whether 68Ga-PSMA PET/CT could improve the accuracy of T staging;3)to explore whether standard uptake value(SUV)on 68Ga-PSMAPET/CT could predict cancer aggressiveness;4)to explore the impact of six months of ADT on tumor visibility on 68Ga-PSMA PET/CT.Methods:Patients underwent 68Ga-PSMA PET/CT and/or mpMRI before radical prostatectomy with complete postoperative pathological results were retrospectively enrolled.The following analysis were performed.1):The diagnostic performance of csPCa by different imaging tools was analyzed by receiver operating characteristics(ROC)analysis.Specific improvement for lesions with different PI-RADS score were analyzed by net reclassification improvement(NRI)2)68GaPSMA PET/CT,mpMRI and postoperative whole mount histology were used for T staging of intermediate-high risk prostate cancer patients and the diagnostic performance for extracapsular extension(ECE)and seminal vesicle invasion(SVI)were analyzed.The impact of additional PET/CT scanning on therapeutic decision were also analyzed.4)68Ga-PSMAPET/CT results were corrected with whole mount histology.The relationship between SUVs and tumor aggressiveness related indictors including Gleason score,T stage,initial PSA and tumor size were analyzed.4)For the patients received six months of androgen deprivation therapy(ADT),SUVs on prostate cancer lesions before treatment were compare with those after treatment.Results:1)Ninety lesions from 54 patients were included in the analysis,of which 66 lesions were csPCa.ROC analysis revealed that 68Ga-PSMA PET/CT combined with mpMRI(com-MRI/PET)had a better performance than mpMRI alone(ΔAUC:0.06,p<0.05).By the calculated cutoff values,com-MRI/PET had a higher sensitivity for csPCa(89%vs 76%,p<0.01),without a sacrifice of specificity(96%vs 88%,p>0.480).The main improvement in diagnostic improvement occurred on lesions with PI-RADS 3.2)Among the 54 included patients,17 had tumor limited in the prostate gland,25 only had ECE and 12 patients had both SVI and ECE on pathology.68Ga-PSMAPET/CT alone or com-MRI/PET had a higher sensitivity on ECE than mpMRI alone(78%versus 54%,p<0.05 and 83%versus 54%,p<0.05).No difference was found between the three scannings for SVI detection.After the additional evaluation of 68Ga-PSMA PET/CT,18.5%(10/54)turned from nerve-sparing surgery to non-nerve sparing surgery.3)Both SUVmax and SUVmean positively correlated with Gleason scores(Spearman r=0.546 and 0.359),initial PSAlevel(Spearman r=0.568 and 0.529)and tumor volume(Spearman r=0.635 and 0.590).T3 tumors had higher SUVmax(11.8(IQR:8.8-24.5)versus 6.4(IQR:4.2-10.5),p<0.01)and higher SUVmean(7.5(IQR:5.2-14.1)versus 5.0(IQR:3.8-7.8),p<0.01)than T2 tumors.4)Compared with baseline 68Ga-PSMA PET/CT,a SUV-reduction occurred in 97.7%(42/43)of the primary PCa(p<0.001),and in 100%(44/44)of the lymph node metastases(p<0.001)six months after initiation of ADT.There is a positive correlation between the decline percentages of PSA and SUV.Conclusions:The com-MRI/PET improves the detection of csPCa for lesions with PIRADS 3 and 68Ga-PSMA PET/CT has a higher sensitivity on ECE detection.SUVs on 68Ga PSMA PET/CT positively correlated with prostate cancer aggressiveness.Meanwhile,continuous ADT significantly reduced the tumor visibility on 68Ga-PSMA PET/CT.