Comparison of ¹⁸F-PSMA-1007 PET/CT with ⁶⁸Ga-PSMA-11 PET/CT for initial staging in intermediate and high-risk prostate cancer - A Pilot Study

Introduction: ¹⁸F-PSMA-1007 is a novel PET radio-tracer that offers several potential advantages over ⁶⁸Ga-PSMA-ligands owing to its non-renal excretion (allowing better identification of lesions close to the urinary bladder/ureter), favorable pharmacokinetics, decay characteristics and mode of production. Existing literature suggests ¹⁸F-PSMA-1007 has comparable or higher detection rates than ⁶⁸Ga-labeled PSMA ligands in prostate cancer patients with biochemical recurrence. In this pilot study, we aimed to conduct a head-to-head comparison of ¹⁸F-PSMA-1007 PET/CT with ⁶⁸Ga-PSMA-11 PET/CT for initial staging in patients with intermediate and high-risk prostate cancer.

Methods: 12 treatment naïve patients with biopsy proven intermediate and high risk (having at least one of the following features: Clinical T stage cT2b or higher, Gleason Grade Group >=2, Serum PSA level >= 10ng/ml) prostate cancer were prospectively recruited. Each patient underwent PET/CT with ¹⁸F-PSMA-1007 and ⁶⁸Ga-PSMA-11 within a time gap of 2 weeks. All the PET/CT studies were independently reviewed by two certified nuclear medicine physicians. Non‐physiologic, abnormal sites of uptake of the radiotracer, higher than the background tracer uptake consistent with the disease process (primary in the prostate or metastatic lesions) after ruling out common pitfalls associated with PSMA ligand PET/CT were taken as positive disease foci. The assessment of both set of images included delineating the number and characteristics of the primary lesion, number of loco‐regional and distant metastatic lesion(s) and measurement of the intensity of tracer uptake (SUVmax). miPSMA expression score was also assigned to the lesions.

Results: Our study population consisted of 12 patients with a mean age of 63 ± 13.1 years (range, 56-84 years). Gleason score of the primary tumor had a median value of 7 (range 5-9), and mean PSA value was 61.3 ng/ml ± 60.29. Intra-prostatic lesions were detected in all patients. In 6 (50%) patients, regional lymph nodes (n=28) were detected. Extra-regional lymph nodes (n=6) were detected in 2 (16.7%) patients. Skeletal metastatic lesions (n=14) were detected in 4 (33.3%) patients. Extra-skeletal metastatic lesions were detected in only one patient (bilateral lung nodules). All sites of primary prostatic malignancy and lymph nodal metastases detected by ⁶⁸Ga-PSMA-11 PET/CT were also detected by ¹⁸F-PSMA-1007 PET/CT. In two patients, additional skeletal lesions (n=2) were detected on ¹⁸F-PSMA-1007 PET/CT. However, these lesions did not change the overall M-stage of the patient. The mean SUVmax in the concordant PSMA-positive prostatic lesions was slightly higher with ¹⁸F-PSMA as compared to ⁶⁸Ga-PSMA (22.38 ± 8.41 vs. 21.46 ± 7.92, p=0.786, n=12). However, this difference was not statistically significant. The mean tumor to background ratios showed no significant difference using the mediastinal blood pool (p=0.40), spleen (p=0.31) and the parotids (p=0.974) as reference organs.

Conclusions: This pilot study demonstrated that ¹⁸F-PSMA-1007 PET/CT is comparable to the currently used ⁶⁸Ga-PSMA-11 PET/CT in detection of primary and metastatic lesions of prostate cancer. Few additional lesions may be detected on ¹⁸F-PSMA PET/CT but their impact on staging is unclear. ¹⁸F-PSMA-1007 owing to its non-renal excretion, cyclotron-based production (enabling more patients to be scheduled each day) in addition to favorable decay characteristics (higher positron yield and shorter positron range) represents a highly promising alternative to ⁶⁸Ga-PSMA-11 for PSMA-PET/CT based initial staging in intermediate and high risk prostate cancer.

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