Competition ('Steal' Phenomenon) between [⁶⁸Ga]Ga-PSMA-11 Uptake in Prostate Tumor Tissue Versus Healthy Tissue

We aimed to clarify whether a steal 'phenomenon' exists by investigating if uptake of 'prostate specific membrane antigen' (PSMA) in prostate tumor tissue correlates with the uptake in healthy tissue. Patients with prostate cancer referred for a [⁶⁸Ga]Ga-PSMA-11 PET/CT were identified retrospectively. Semi-automated quantitative image analysis was performed; fractional healthy tissue [⁶⁸Ga]Ga-PSMA-11 uptake volume (HT-PSMA (SUV*cm³)) in the lacrimal, submandibular, and parotid glands, and kidneys, and the fractional total lesion [⁶⁸Ga]Ga-PSMA-11 uptake volume (TL-PSMA (SUV*cm³)) of prostate cancer were used. Ninety-two patients, age 78 ± 8 years, were analyzed. Median TL-PSMA was 703.37 SUV*cm³ (IQR 119.56-2778.20), median HT-PSMA of the lacrimal, submandibular, and parotid glands, and kidneys was: 13.69 (IQR 7.29-19.06), 194.75 (IQR 133.67-276.53), 552.54 (IQR 379.98-737.16), and 8092.75 SUV*cm³ (IQR 5793.02-11,385.86), respectively. A significant (p-value ≤ 0.001) but weak-moderate correlation was found between the TL-PSMA and HT-PSMA of the parotid- and submandibular glands, and kidneys (correlation coefficient of -0.447, -0.345, and -0.394, respectively). No correlation was found between TL-PSMA and HT-PSMA of the lacrimal glands. The existence of a 'steal' phenomenon cannot be confirmed in this study. Healthy tissue uptake of [⁶⁸Ga]Ga-PSMA-11 is only partially influenced by TL-PSMA. Thus, modification of therapeutic PSMA activity should not be adjusted based on TL-PSMA alone.