First Southeast Asian Experience of Terbium-161 PSMA Therapy for Metastatic Castration-Resistant Prostate Cancer (mCRPC): Quantitative Imaging and Dosimetric Approach

Prostate-specific membrane antigen (PSMA)-targeted radionuclide therapy has become an established treatment option for metastatic castration-resistant prostate cancer. Although lutetium-177 (¹⁷⁷Lu) PSMA therapy has shown promising clinical benefits, terbium-161 (¹⁶¹Tb) PSMA is an emerging theranostic agent offering potential advantages due to its combination of beta and Auger electron emissions. This work presents the first documented case in Thailand and Southeast Asia of a patient treated at Ramathibodi Hospital with ¹⁶¹Tb-PSMA following progression on ¹⁷⁷Lu-PSMA therapy. This report describes the clinical application of this novel radiopharmaceutical, the implementation of quantitative imaging protocols, single photon emission computed tomography/computed tomography calibration processes, and absorbed dose estimations from voxel-based dosimetry that contributed to individualised treatment planning.