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Novel System for Delivery of Electron Dose From Short Lived Isotopes

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R O'Brien

R O'Brien*, W Culbreth, University of Nevada, Las Vegas, Las Vegas, NV

SU-E-T-314 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To evaluate feasibility of delivering electron dose by use of the extremely short lived isotope In-116 undergoing beta decay. Methods of isotope creation, transport and delivery are also examined.

Methods: A system consisting of natural Indium in a eutectic liquid metal was constructed to transport by peristaltic pumping in flexible tubing the isotope In-116 between a neutron activation source and a phantom material where beta decay is measured. The In-116 (half-life 14.1 sec), created through thermal neutron capture on In-115, decays with 99.98% probability by beta particle with an energy average of 1.37 MeV and endpoint energy of 3.28 MeV. The liquid metal was passed near the neutron source for 4 half-lives, pumped to a thin window chamber (0.13mm styrene), and held stationary for 60 seconds to detect beta particles with a silicon charged particle detector.

Results: The liquid nature of the eutectic allowed pumping of the material through tubing from the neutron source to the detector. By keeping the tubing narrow the mixture remained in smooth laminar flow to maintain a bolus of active material (In-116) that reaches the detector with good uniformity. Beta decays were detected in the silicon detector with a half-life matching that of In-116 showing that dose can be successfully delivered to a material.

Conclusion: This work indicates the potential for targeted electron dose useful for shallow lesions currently treated by electrons or low energy X-Rays. The lack of associated gamma-rays and pure beta source allows dose to be tightly controlled to the treatment area and the application of custom fields based on applicator shape. Rapid decay to stable Sn-116 means no permanent isotopes are used and a reduction in shielding requirements. Future investigation includes ion chamber measurements for depth dose and the use of higher flux neutron sources to examine clinically useful doses.

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