Actinium Therapy for Late-stage Aggressive Sarcomas

\[Ac225\]RTX-2358 will be given as an intravenous injection once every 8 weeks for up to 6 doses. Each group (3 total) will receive a set administered activity level (dose) of \[Ac 225\]RTX 2358 given once every 8 weeks. The first group will received the lower dose, the second group will received the mid level dose, and the third group the highest dose. A Safety Review Committee will determine when/if it is appropriate to allow the next group to proceed.

\[Cu64\]LNTH-1363S is a investigational radioactive diagnostic imaging agent to demonstrate that the tumor expresses Fibroblast Activation Protein. An imaging test is performed after a single injection with \[Cu64\]LNTH-1363S 13-35 days before the first administration of study drug \[AC225\]RTX-2358 to confirm that the sarcoma has FAP expression.