Clinical parameters and nomograms for predicting lymph node metastasis detected with 68Ga‐PSMA‐PET/CT in prostate cancer patients candidate to definitive radiotherapy

Abstract Background Defining the extent of disease spread with imaging modalities is crucial for therapeutic decision‐making and definition of treatment. This study aimed to investigate whether clinical parameters and nomograms predict prostate‐specific membrane antigen (PSMA)‐positive lymph nodes in treatment‐naïve nonmetastatic prostate cancer (PC) patients. Materials and Methods The clinical data of 443 PC patients (83.3% high‐risk and 16.7% intermediate‐risk) were retrospectively analyzed. Receiver operating characteristic (ROC) curves with areas under the curve (AUC) were generated to evaluate the accuracy of clinical parameters (prostate‐specific antigen [PSA], T stage, Gleason score [GS], International Society of Urological Pathology [ISUP] grade) and nomograms (Roach formula [RF], Yale formula [YF], and a new formula [NF]) in predicting lymph node metastasis. The AUCs of the various parameters and clinical nomograms were compared using ROC and precision‐recall (PR) curves. Results A total of 288 lymph node metastases were identified in 121 patients (27.3%) using 68 Ga‐PSMA‐11‐positron emission tomography (PET)/computed tomography (CT). Most PSMA‐avid lymph node metastases occurred in external or internal iliac lymph nodes (142; 49.3%). Clinical T stage, PSA, GS, and ISUP grade were significantly associated with PSMA‐positive lymph nodes according to univariate logistic regression analysis. The PSMA‐positive lymph nodes were more frequently detected in patients with PSA >20 ng/ml, GS ≥7 or high risk disease compared to their counterparts. The clinical T stage, serum PSA level, GS, and ISUP grade showed similar accuracy in predicting PSMA‐positive metastasis, with AUC values ranging from 0.675 to 0.704. The median risks for PSMA‐positive lymph nodes according to the RF, YF, and NF were 31.3% (range: 12.3%–100%), 22.3% (range: 4.7%–100%), and 40.5% (range: 12.3%–100%), respectively. The AUC values generated from ROC and PR curve analyses were similar for all clinical nomograms, although the RF and YF had higher accuracy compared to NF. Conclusion The clinical T stage, PSA, GS, and ISUP grade are independent predictors of PSMA‐positive lymph nodes. The RF and YF can be used to identify patients who can benefit from 68 Ga‐PSMA‐11 PET/CT for the detection of lymph node metastasis. Together with nomograms, 68 Ga‐PSMA‐11 PET/CT images help to localize PSMA‐positive lymph node metastases and can thus assist in surgery and radiotherapy planning.