Medical Isotope Production of Actinium 225 By Linear Accelerator Photon Irradiation of Radium 226

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Date
2013-06-12
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Publisher
Virginia Tech
Abstract

There is a present and future need for the medical isotope Actinium-225, currently in short supply worldwide.  Only a couple manufacturers produce it in very low quantities.  In roughly the past 10 years the medical community has explored the use of Ac-225 and its daughter Bismuth-213 for targeting a number of differing cancers by way of Targeted Alpha Therapy (TAT). This method utilizes the alpha-decay of both Ac-225 (half-life 10 days) and Bi-213 (half-life 46 min) to kill cancerous cells on a localized basis.  Maximum energy is delivered to the cancer cells thereby greatly minimizing healthy tissue damage.

This research proposes a production method using a high-energy photon spectrum (generated by a linear accelerator or LINAC) to irradiate a sample of Radium-226 (half-life 1600yrs).  The photo-neutron reaction liberates neutrons from Ra-226 atoms leaving behind Radium-225 (half-life 14.7 days).  Ra-225 decays naturally through beta emission to Ac-225.  Previous research demonstrated it is possible to produce Ac-225 using a LINAC; however, very low yields resulted which questioned the feasibility of this production method.  This research proposes a number of LINAC and radium sample modifications that could be greatly increase yield amounts for practical use.

Additionally, photo-neutron cross-section data for Ra-226 was used, which led to improved yield calculations for Ra-225.  A MATLAB® model was also created, which enables users to perform quick yield estimates given several key model parameter inputs.  Obtaining a sufficient supply of radium material is also of critical importance to this research.  Therefore information was gathered regarding availability and inventory of Radium-226.  This production method would serve as a way to not only eliminate many hazardous radium sources destined for interim storage, but provide a substantial supply of Ac-225 for future cancer treatment.

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Keywords
Radium-226, Actinium-225, Medical Isotopes, Linear Accelerator (LINAC), Photonuclear Cross-section
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