Preliminary comparative study between ¹⁸F-PSMA-1007 and ⁶⁸Ga-PSMA-11 PET/CT in patients with prostate cancer: biodistribution and tumor detection

Objectives: ⁶⁸Ga-PSMA-11 (prostate-specific membrane antigen) PET/CT has recently showed significant impact in the management of prostate cancer (PCa). The main disadvantage of this tracer is its urinary route of excretion, resulting in high bladder activity, which is often found to obscure pelvic lesion detection. ¹⁸F-PSMA-1007 is a novel PSMA-ligand with minimal urinary excretion; therefore, we aim to evaluate the biodistribution and PCa lesion detection of ¹⁸F-PSMA-1007 at 60 and 120 min and compare with ⁶⁸Ga-PSMA-11 PET/CT in the same cohort of patients.

Methods: 11 PCa patients (age range: 55-81 y, mean=67.6±7.1 y) were recruited into this study. They firstly underwent whole-body ⁶⁸Ga-PSMA-11 PET/CT (Biograph mCT) at 60 min post injection (98±10 MBq) with a 3 min/bed acquisition. Within 3 days, the same patients underwent ¹⁸F-PSMA-1007 (270±28 MBq) PET/CT with the same scanner at 60 and 120 min, respectively, at 2 min/bed acquisition. Normal organ biodistribution and tumor uptake were examined for the ⁶⁸Ga-PSMA-11 and 2 sets of ¹⁸F-PSMA-1007 PET images. Mean SUV (SUV_mean) in normal tissue was measured in the bladder, blood pool, bone marrow (3^rd lumbar vertebral body), gluteus muscle, gall bladder, intestine, kidneys, lacrimal gland, liver, lung, salivary gland, spleen. Maximum SUV (SUV_max) in malignant lesions was measured within volumes of interest (MIMContouring 6.4) for all 3 sets of PET/CT. Results: The biodistribution of ⁶⁸Ga-PSMA-11 and ¹⁸F-PSMA-1007 at 60 and 120 min is tabulated below. ¹⁸F-PSMA-1007 activity in bladder at both time points was significantly lower than ⁶⁸Ga-PSMA-11 (both P<0.05). Gall bladder had the highest¹⁸F-PSMA-1007 activity, in keeping with hepatobiliary excretion. Comparing with ⁶⁸Ga-PSMA-11, ¹⁸F-PSMA-1007 uptake was also significantly lower in the kidneys, but higher in the liver (all P<0.05). The other organs were similar in SUV_mean among them. For PCa lesion detection (primary: 15, lymph node: 22, bone: 13, lung: 3, liver: 1), ¹⁸F-PSMA-1007 PET/CT at 60 and 120 min found the same number of lesions, but SUV_maxincreased over time (13.6±11.1 vs 17.2±14.2) with a median of 22%, while blood-pool activity decreased by 31 %, with improved lesion-to-background ratios (LBR). ⁶⁸Ga-PSMA-11 PET/CT missed 1/15 PCa lesion (adjacent to the bladder wall) and was equivocal in 1 primary lesion (SUV_max=3.9). For lymph node and distant metastases, ¹⁸F-PSMA-1007 PET/CT at 120 min was concordant with ⁶⁸Ga-PSMA-11 and the LBRs were similar (17.7±14.2 vs 17.1±13.3). However, ⁶⁸Ga-PSMA-11 had higher LBR for liver metastasis (2.3 vs 2).

Conclusions: Our preliminary results agreed that ¹⁸F-PSMA-1007 PET/CT may have the potential as an alternative tracer besides ⁶⁸Ga-PSMA-11 for the detection of PCa, especially for imaging at 120 min. It may facilitate lesion detection in the pelvis but increased accumulation in the liver may reduce the efficacy for detection of liver metastases.