Actinium Therapy for Late-stage Aggressive Sarcomas

The goal of this clinical trial is to learn about the safety of drug \[Ac225\]RTX-2358 and the diagnostic imaging agent \[Cu64\]LNTH-1363S. Additionally Ratio Therapeutics will learn if \[Ac225\]RTX-2358 drug is effective in treating advanced sarcoma. The main questions the study aims to answer in Phase/Part 1 of the trial are: * Is \[Ac225\]RTX-2358 tolerable or does it cause toxicities (medical problems) in patients. * What is the most tolerable dose of \[Ac225\]RTX-2358 * Does the treatment show effectiveness on advanced sarcoma Participants will: * Take drug \[Ac225\]RTX-2358 once every 8 weeks (4 cycle target; 6 cycle maximum) over a period of 12 months * Visit the clinic three times for the first week of cycle one, then once a week for the remaining 7 weeks of cycle 1 for check-ups and tests. * For cycles 2-6: patient will visit the clinic once every 2 weeks for checkups and tests * Remain in long term follow-up for a period of four additional years