Abstract
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Introduction: Hitherto no randomised prospective trial data has been published for [18F]PSMA-1007. This protocol planned sub-study compares intra-individual [18F]PSMA-1007 and [68Ga]Ga-PSMA-11 for healthy organs and target lesions to see if parametric analysis might reveal insights into in vivo radiopharmaceutical behaviour and in the characterisation of malignant tissues.
Methods: 10 patients with biochemically recurrent prostate cancer underwent both [68Ga]Ga-PSMA-11 (PSMA-11) or [18F]PSMA-1007 (PSMA-1007) PET/CT in randomised order as part of planned and approved sub-analysis of a prospective comparative imaging trial (NCT05079828) which shall recruit N=100 patients. Trial entry and exclusion criteria as well as endpoints are as previously published. Dynamic scans were acquired from 0 to 60 minutes using a long-axial field-of-view PET/CT with static imaging performed at 2h p.i. Healthy tissue and lesion segmentation was performed by a board certified nuclear medicine physician using 40% iso-contour where appropriate. Following model selection, data were fitted using a reversible two-tissue compartment (2TC) model. Non-specific activity at ganglia and foci of unspecific bone uptake (UBU) were also included. Values were compared using paired t-tests.
Alberts I, Bütikofer L, Rominger A, Afshar-Oromieh A (2022) A randomised, prospective and head-to-head comparison of [68Ga]Ga-PSMA-11 and [18F]PSMA-1007 for the detection of recurrent prostate cancer in PSMA-ligand PET/CT—Protocol design and rationale. PLoS ONE 17(7): e0270269. https://doi.org/10.1371/journal.pone.0270269
Results: Preliminary analysis of the target lesions showed no statistically significant differences or appreciable trends in tracer delivery (K1) for any tissue type or organ or between tracers. Faster (non-significant) binding was observed for K3 for PSMA-11 (see fig. 1), but also with faster K4, suggesting reversible kinetics. For PSMA-1007 K4 was very low for all lesion types, in-keeping with irreversible kinetics (see fig. 2). For all lesions, including UBU, no significant differences were seen for the specific distribution volume (Vs) suggesting that non-specific binding is not the cause of the higher frequency of UBU seen in PSMA-1007 or of ganglia in PSMA-11. For net influx Ki statistical significance was reached for nodal ganglia and borderline higher net influx for local recurrence (p=0.08) for PSMA-11.
Conclusions: Parametric analysis showed clear intravidual in vivo differences in tracer kinetics, with irreversible kinetics seen in [18F]PSMA-1007 and reversible kinetics for [68Ga]Ga-PSMA-11. A statistically higher net influx was seen for [68Ga]Ga-PSMA-11 in Ganglia. Otherwise, there were no clear differences were seen for both tracers with largely comparable kinetics in most normal organs and malignant lesions. Parametric imaging could not reveal differences between malignant lesions and non specific foci (e.g. UBU).
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