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Comparison of the Radiation and Thermal Dose Distributions of a Novel Thermo-Brachytherapy Seed

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G Warrell

G Warrell*, D Shvydka, B Gautam, E Parsai, University of Toledo Medical Center, Toledo, OH

WE-A-BRB-4 Wednesday 8:00:00 AM - 9:55:00 AM Room: Ballroom B

Purpose:
A novel thermo-brachytherapy seed implant recently developed by our group combines a radioactive source (I-125) with a ferromagnetic core, capable of producing heat when placed in an alternating magnetic field. The seed is intended for concurrent hyperthermia and brachytherapy treatments for deep-seated solid tumors. The maximized heat production is achieved when all implants are aligned along the magnetic field direction. For optimal coverage, the planned thermal and radiation dose distributions should be closely matched. As the algorithm used by the commercial treatment planning software is inadequate for accurate calculation of the dose distribution from parallel seeds at short distances, a Monte Carlo (MC) model was developed and utilized for comparison of the radiation and thermal distributions.

Methods:
A model consisting of an array of seeds separated from each other by 1 cm, oriented parallel to the magnetic field direction, was studied in a cylindrical water phantom. The radiation dose distribution was obtained with the MC code MCNP5. The thermal distribution was modeled for various magnetic field intensities and frequencies, and accounts for heat loss due to blood perfusion using a finite element analysis (FEA) package COMSOL Multiphysics.

Results:
A radiation dose distribution obtained from the MC calculations accounts for the interseed shielding effect and assumes non-random (parallel) orientation of the seeds. A comparison between this dose distribution and thermal coverage data calculated by the FEA method shows that they may be made to coincide closely by adjusting the magnetic field intensity and frequency.

Conclusions:
Maximum heating and optimal thermal coverage are obtained when the thermo-brachytherapy seeds are orientated in the direction of the magnetic field. For a specific seed placement a thermal distribution similar to the radiation dose distribution can be achieved via seed alignment and adjustments of the frequency and intensity of the applied magnetic field.

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