Targeted radionuclide therapy delivers ionizing radiation to tumor cells through the accumulation of intravenously injected radiopharmaceuticals. In the case of metastatic castration-resistant prostate cancer, the currently used agent [177Lu]Lu-PSMA-617 is limited by side effects from the accumulation of radioligand in non-tumor tissues and the moderate biological efficacy of 177Lu. To address these shortcomings, [161Tb]Tb-SibuDAB was developed at ETH Zurich/Paul Scherrer Institute. An added albumin-binding moiety enhanced the blood circulation time and, hence, increased the tumor dose while reducing off-target accumulation. Open questions remain as to the overall tolerability of [161Tb]Tb-SibuDAB and its effectiveness in neutralizing bone metastases. The objective is to conduct a tolerability and efficacy study of [161Tb]Tb-SibuDAB in two different rodent models. If tolerability and efficacy can be ascertained, [161Tb]Tb-SibuDAB will be introduced into clinical use in Switzerland in a phase I trial.