The invention is directed to a microsphere, a method for preparing the microsphere, a powder comprising a number of the microspheres, a suspension comprising the microsphere or the powder, the use of the microsphere, a method for detecting a tumour, and a therapeutic composition comprising the microsphere, the powder, or the suspension. The microsphere of the invention comprises a lanthanide metal complex wherein the lanthanide metal is present in an amount of more than 20 wt.%, based on total weight of the microsphere, and wherein the lanthanide metal complex comprises a lanthanide ion and phosphate.
