Matched-Pair Comparison of 68Ga-PSMA-11 PET/CT and 18F-PSMA-1007 PET/CT: Frequency of Pitfalls and Detection Efficacy in Biochemical Recurrence After Radical Prostatectomy

Abstract

¹⁸F-labeled prostate-specific membrane antigen (PSMA)-ligand PET has several principal advantages over ⁶⁸Ga-PSMA-11. The purpose of this retrospective study was to evaluate the frequency of non-tumor-related uptake and the detection efficacy comparing ⁶⁸Ga-PSMA-11 PET/CT and ¹⁸F-PSMA-1007 PET/CT in recurrent prostate cancer (PC) patients. Methods: The study included 102 patients with biochemically recurrent PC after radical prostatectomy undergoing ¹⁸F-PSMA-1007 PET/CT imaging. On the basis of various clinical variables, patients with corresponding ⁶⁸Ga-PSMA-11 PET/CT scans were matched. All PET/CT scans (n = 204) were reviewed by 1 nuclear medicine physician. First, all PET-positive lesions were noted. Then, lesions suspected of being recurrent PC were differentiated from lesions attributed to a benign origin on the basis of known pitfalls and information from CT. For each region, the SUV_max of the lesion with the highest PSMA-ligand uptake was noted. Detection rates were determined, and SUV_max was compared separately for ⁶⁸Ga-PSMA-11 and ¹⁸F-PSMA-1007. Results: In total, ¹⁸F-PSMA-1007 PET and ⁶⁸Ga-PSMA-11 PET revealed 369 and 178 PSMA-ligand-positive lesions, respectively. ¹⁸F-PSMA-1007 PET revealed approximately 5 times more lesions attributed to a benign origin than did ⁶⁸Ga-PSMA-11 PET (245 vs. 52 lesions, respectively). The benign lesions most frequently observed were ganglia, unspecific lymph node, and bone lesions, at a rate of 43%, 31%, and 24% for ¹⁸F-PSMA-1007 PET and 29%, 42%, and 27% for ⁶⁸Ga-PSMA-11 PET, respectively. The SUV_max of lesions attributed to a benign origin was significantly higher (P < 0.0001) for ¹⁸F-PSMA-1007 PET. Further, a similar number of lesions was attributed to recurrent PC (124/369 for ¹⁸F-PSMA-1007 PET and 126/178 for ⁶⁸Ga-PSMA-11 PET). Conclusion: The number of lesions with increased PSMA-ligand uptake attributed to a benign origin is considerably higher for ¹⁸F-PSMA-1007 PET than for ⁶⁸Ga-PSMA-11 PET. This finding indicates the need for sophisticated reader training emphasizing known pitfalls and reporting within the clinical context.

Keywords: PET/CT; PSMA; genitourinary; oncology; pitfalls; prostate cancer.

FIGURE 1.

(A) Distribution of suggestive and benign lesions for all PSMA-ligand–positive lesions on ⁶⁸Ga-PSMA-11 PET/CT and ¹⁸F-PSMA-1007 PET/CT. (B) Origin of lesions attributed to benign origin on ⁶⁸Ga-PSMA-11 PET/CT and ¹⁸F-PSMA-1007 PET/CT.

FIGURE 2.

CT images (top) and ¹⁸F-PSMA-1007 PET/CT images (bottom) of patient presenting with PSMA-ligand–positive, typically tear-drop–shaped cervical ganglia on both sides prevertebrally (A and D), unspecific PSMA-ligand uptake in nonenlarged left inguinal LN (B and E), and focal PSMA-ligand uptake in nondisplaced fracture of rib with corresponding fracture line and callus formation on CT images (C and F).

FIGURE 3.

(A–C) Baseline ¹⁸F-PSMA-1007 PET/CT of 65-y-old patient with BCR PC after RPE presenting with PSA value of 1.4 ng/mL. Images show single PSMA-positive LN metastasis pararectally (A, arrow). (D) This LN was removed during PSMA radioguided surgery, with subsequent PSA decline to <0.2 ng/mL and follow-up ¹⁸F-PSMA-1007 PET/CT showing no PSMA ligand uptake anymore. In this patient, unspecific focal PSMA ligand uptake in right fourth rib was observed (B, arrow; SUV_max, 4.4) and was still present on follow-up PET/CT (E, SUV_max, 4.6), with no morphologic correlate on corresponding CT images (C and F).