Improved specific activity of reactor produced 117mSn with the Szilard-Chalmers process

We report an investigation of the application of the Szilard-Chalmers process to improve the specific activity of reactor produced ^117mSn. The radiopharmaceutical ^117mSn⁴⁺DTPA is a promising agent for relieving bone pain in breast and prostate cancer patients. Preliminary studies in these patients have given very encouraging results. For this application high specific activity ^117mSn is required to minimize the quantity of administered DTPA. Using a tetraphenyltin target we have investigated solvent extraction and ion exchange techniques to enrich the radioactive atom concentration. Other variables studied include the effect of neutron flux, total neutron fluence and sample mass. The enrichment factor was comparable for both solvent extraction and ion exchange techniques, but solvent extraction was more convenient. For 1 h irradiations the enrichment factor averaged ∼ 70 but declined to ∼ 2 after 24 h irradiation due to accumulated radiation damage. The enrichment factor also declined with increasing neutron energy. An isotope effect on the Szilard-Chalmers process was observed as the enrichment factor for ¹¹³Sn was consistently higher than for ^117mSn.