The aim of our study was to evaluate the tumor-targeting properties, therapeutic efficacy, and tolerability of [225Ac]Ac-DOTA-hG250 (225Ac-hG250) RIT in comparison to [177Lu]Lu-DOTA-hG250 (177Lu-hG250) in mice bearing CAIX-expressing human ccRCC xenografts. The gene discussed is CA9; the disease is neoplasm.