Outlined is a method of treating a tumour or other lesion wherein a solution comprising one or more radioactive isotopes is introduced directly into said tumour or lesion to effect in situ precipitation of a radioactive precipitate in the tumour or lesion. Preferably the radioactive precipitate is formed through interaction of the solution with endogeneous substances in tissue, such as calcium. Preferred radioisotopes include phosphorus-32 or 33, yttrium-90, strontium-89, iodine-131, samarium-153, ruthenium-103, iodine-125 and palladium-103. The solution may comprise a combination of radionuclides of different energy profiles (e.g. beta decay, electron capture decay, gamma decay) and/or a chelating agent. Examples relate to a 32P or 33P radiophosphate solution (e.g. sodium hydrogen phosphate) forming a radioactive calcium phosphate precipitate following intra-tumoural injection. The method advantageously combines radiation therapy with a thrombogenic effect and may be useful in treating hyperproliferative diseases including colorectal cancer, lung cancer, prostate cancer, breast cancer or brain cancer.
