The invention provides a method for the treatment of soft tissue disease in a mammalian subject (preferably a human or canine subject), said method comprising administering to said subject a therapeutically effective quantit y of a soft tissue targeting complex of thorium-227 and a complexing agent, wherein said quantity is such that an acceptably non-myelotoxic quantity of radium-223 is generatedin vivo by nuclear decay of the administered thorium - 227.