Evaluation of [18F]PSMA-1007 uptake variability in patients with prostate cancer

The biodistribution of PSMA-ligands is of interest in radionuclide therapy planning. We investigated the variability of [¹⁸F]PSMA-1007 uptake in organs at risk and in relation to tumour burden in prostate cancer patients.

A total of 1086 patients who underwent PSMA PET-CT for staging or recurrence of prostate cancer were included. Total lesion volume (TLV) and total lesion uptake (TLU) were calculated from manual segmentations. The mean standardized uptake value (SUV_mean) in the organs at risk kidneys, liver, parotid glands and spleen was obtained. Correlations between TLV/TLU and SUV_mean in normal tissues were calculated using Spearman rank correlation. SUV_mean in normal tissues was stratified into groups based on TLV.

The median (IQR) SUV_mean of the kidneys, liver, parotid glands, and spleen was 13.1 (IQR 4.6), 11.8 (4.4), 18.6 (6.8) and 11.3 (5.8), respectively. The median TLV was 3.8 cm³ (9.7) and median TLU was 31.2 cm³ (106.3). There was no significant correlation between TLV or TLU and SUV_mean for the liver, parotid glands, or spleen, but a weak negative correlation between TLV/TLU and SUV_mean in the kidneys (r = -0.011, p = 0.0005; r = -0.09, p = 0.003). There was a tendency towards a lower SUV_mean in the kidneys and parotid glands in patients with a very high TLV.

There was a large uptake variability in organs at risk, which demonstrates the need for individual pretherapy dosimetry. There may be a tumour sink effect in the kidneys and parotid glands in patients with a very high TLV.