title: A theoretical model for the production of Ac-225 for cancer therapy by photon-induced transmutation of Ra-226.
abstract: Radium needles that were once implanted into tumours as a cancer treatment are now obsolete and constitute a radioactive waste problem, as their half-life is 1600 years. We are investigating the reduction of radium by transmutation on a small scale by bombarding Ra-226 with high-energy photons from a medical linear accelerator (linac) to produce Ra-225, which subsequently decays to Ac-225, which can be used as a generator to produce Bi-213 for use in 'targeted alpha therapy' for cancer. This paper examines the possibility of producing Ac-225 with a linac using an accurate theoretical model in which the bremsstrahlung photon spectrum at 18 MV linac electron energy is convoluted with the corresponding photonuclear cross sections of Ra-226. The total integrated yield can then be obtained and is compared with a computer simulation. This study shows that at 18 MV, the photonuclear reaction on Ra-226 can produce low activities of Ac-225 with a linac. However, a high power linac with high current, pulse length and frequency is needed to produce practical amounts of Ac-225 and a useful reduction of Ra-226.
authors.affiliation: Centre for Experimental Radiation Oncology, St. George Cancer Care Centre, Gray St. Kogarah, NSW, Australia. gmelvill@bigpond.net.au
authors.forename: G
authors.initials: G
authors.lastname: Melville
authors.forename: Sau
authors.initials: S
authors.lastname: Fan Liu
authors.forename: B J
authors.initials: BJ
authors.lastname: Allen
mesh_terms: D000186:Actinium / Q000737:chemistry*; D003198:Computer Simulation; D008962:Models, Theoretical; D009369:Neoplasms / Q000532:radiotherapy*; D017785:Photons; D011876:Radionuclide Generators; D011883:Radium / Q000737:chemistry*
chemical_list: D000186:Actinium; D011883:Radium