ABSTRACT
Background@#PSMA-targeted radiopharmaceuticals have been widely studied for their theragnostic role in prostate cancer and were introduced in the Philippines in 2018. The optimal administered activity of 177Lu-PSMA for targeted endoradiotherapy has not yet been established and is thought to be influenced by several factors, including tumor burden. This study investigates the effect of tumor burden on the normal tissue PSMA uptake among Filipino patients with prostate cancer using its diagnostic counterpart, 68Ga-PSMA I&T @*Methods@#One hundred four patients imaged with 68Ga-PSMA I&T PET/CT in our institution from January 2018 to May 2020 were included. Patients were visually classified into low, medium, and high tumor burden groups. Maximum and mean standardized uptake values (SUVmax and SUVmean) of the lacrimal glands, parotid glands, submandibular glands, kidneys, liver, spleen, and bone were measured and compared among tumor burden groups. @*Results and Conclusions@#68Ga-PSMA I&T uptake in the kidneys, the salivary glands, and the liver, were significantly reduced by approximately 25-50% in patients with high tumor burden. This finding supports the hypothesis that patients with higher tumor load can tolerate higher activity doses of 177Lu-PSMA for endoradiotherapy before developing significant damage to the critical organs. This may serve as a guide towards optimizing and personalizing 177Lu-PSMA I&T administered activity dose for radionuclide therapy