Assessment of changes in physiologic distribution of 68Ga-PSMA in normal tissues relative to tumor burden in patients undergoing PET/CT for prostate cancer

Purpose: This study aimed to evaluate changes in 68Ga-PSMA (Prostate-specific membrane antigen) uptake in normal tissues according to prostate cancer (PC) tumor burden, as assessed by PET/CT. Materials and Methods: This retrospective study included 213 consecutive patients with histologically confirmed PC who underwent 68Ga-PSMA PET/CT imaging. Based on PET/CT findings, patients were categorized into three groups according to 68Ga-PSMA expression: 1) PSMA-negative prostate cancer; 2) local disease: PSMA uptake limited to the prostate gland and/or pelvic region; 3) metastatic disease: presence of extrapelvic and/or distant PSMA-avid lesions. Results: Among the 213 patients, 68Ga-PSMA PET/CT imaging revealed normal PSMA distribution in 57 patients (26.8%), localized disease in 88 patients (41.3%), and metastatic involvement in 68 patients (31.9%). In the metastatic disease group, the mean SUVmax values were significantly lower in the lacrimal, parotid, and submandibular glands, as well as in the spleen, kidneys, and bowel, compared to the PSMA-negative prostate cancer and local disease groups. In contrast, prostate SUVmax was markedly higher in the metastatic group. Conclusion: This study demonstrates that 68Ga-PSMA uptake in normal tissues decreases with increasing metastatic tumor burden, particularly in salivary glands, kidneys, and lacrimal glands.