Background   There are still limitations in evaluating pelvic lymph node metastasis and local invasion of prostate cancer using single imaging examination such as ¹⁸F-DCFPyL PET/CT or multi-parameter magnetic resonance imaging (mpMRI).

  Objective   To compare the diagnostic efficacy of ¹⁸F-DCFPyL PET/CT and mpMRI alone or in combination for intermediate to high-risk prostate cancer with pelvic lymph node metastasis, extraprostatic extension and seminal vesicle invasion.

  Methods   Clinical data about patients with intermediate to high-risk prostate cancer who underwent ¹⁸F-DCFPyL PET/CT and mpMRI with robotic-assisted laparoscopic radical prostatectomy (RARP) and expanded pelvic lymph node dissection (ePLND) in Chinese PLA General Hospital from January 2018 to June 2022 were retrospectively analyzed. The sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of ¹⁸F-DCFPyL PET/CT, mpMRI and the combination of both for the diagnosis of pelvic lymph node metastasis, extraprostatic extension and seminal vesicle invasion in prostate cancer were compared using the postoperative pathological results as the gold standard.

  Results   A total of 74 patients with intermediate to high-risk prostate cancer were included, with a mean age of (66.8 ± 6.7) years. There were 26 cases (35.1%) in the intermediate-risk group and 48 cases (64.9%) in the high-risk group. The median tPSA value was 15.3 (IQR: 9.4 ~ 26.1) ng/mL, and the preoperative Gleason score was 7 in 33 cases, 8 in 20 cases and ≥9 in 21 cases. ¹⁸F-DCFPyL PET/CT had higher sensitivity (57.1% vs 28.6%) , specificity (98.5% vs 97%), and AUC (0.78 vs 0.63, P=0.106) compared to mpMRI in the diagnosis of pelvic lymph node metastases, and the combination of the two did not show better diagnostic performance (AUC: 0.76 vs 0.78, P=0.154). In detecting seminal vesicle invasion, using mpMRI alone had higher sensitivity (66.7% vs 58.3%) and specificity (95.2% vs 91.9%) than ¹⁸F-DCFPyL PET/CT, with a higher AUC (0.83 vs 0.75, P=0.185), and the combination of the two didn’t improve the diagnostic performance significantly (AUC: 0.83 vs 0.81, P=0.690). In the diagnosis of extraprostatic invasion, the use of mpMRI had higher AUC compared to ¹⁸F-DCFPyL PET/CT alone (0.75 vs 0.64, P=0.007), and no significant improvement was seen when the two were combined (AUC: 0.73 vs 0.75, P=0.152).

  Conclusion   The preoperative combination of mpMRI with ¹⁸F-DCFPyL PET/CT may be useful in assessing seminal vesicle invasion in prostate cancer. The use of ¹⁸F-DCFPyL PET/CT alone, which is highly specific for the diagnosis of pelvic lymph node metastases in intermediate-to-high-risk prostate cancer, can help in making decisions about whether to perform pelvic lymph node dissection. However, the use of mpMRI alone shows better diagnostic accuracy for extraprostatic invasion.