Clinical Impact of Lower-Limb Imaging in Ga-68-PSMA PET/CT for Patients with Prostate Cancer

Abstract

Our purpose was to determine whether there is a clinical benefit to add lower-limb imaging in Ga-68-labeled prostate-specific membrane antigen (PSMA) PET/CT scans for patients with prostate cancer. Methods: In total, 701 patients with prostate cancer who underwent Ga-68-PSMA PET/CT were evaluated retrospectively. All patients underwent additional lower-limb imaging. Images were reanalyzed by experienced nuclear medicine physicians, and metastatic sites were documented. The prostate-specific antigen (PSA) level and Gleason score were also compared with Ga-68-PSMA PET/CT findings. Results: In 601 patients (85.7%), at least 1 tumoral lesion was observed on Ga-68-PSMA PET/CT. The number of patients with bone metastasis in 2 forms was 278 patients (39.6%); 108 (15.4%) were oligometastatic (= 4 metastases). In lower-limb imaging, bone metastasis was detected in 61 patients (8.7%), the specific locations of which were as follows: middle-distal femur (n = 54), tibia (n = 19), fibula (n = 24), and calcaneus (n = 1). Lower-limb metastasis was detected mostly in symptom-positive patients (70.1%) but in only 4% of the symptom-negative group. All patients with lower-extremity metastasis also had multiple bone metastases shown on limited whole-body Ga-68-PSMA PET/CT. The median PSA level was significantly higher in multimetastatic patients with lower-limb metastasis than in those without lower-limb metastasis (P < 0.001, Mann-Whitney U test), but no statistical differences was found in terms of Gleason score (chi(2) = 0.042, P = 0.837). According to receiver-operatingcharacteristic analysis, PSA has a good predictive value for detecting lower-limb metastasis, with 76.6% sensitivity and 72% specificity (using a reference cutoff PSA level of 24 ng/mL [area under the curve, 0.81; 95% confidence interval, 0.74-0.87]). Conclusion: Lower-limb imaging did not change the metastatic status of disease or significantly affect the therapeutic approach. However, if multimetastatic patients present relevant symptoms for lower-limb metastasis, it could be beneficial to consider including lower-limb imaging for possible palliative therapies.