CONICET | Buscador de Institutos y Recursos Humanos

Convergent beam radiotherapy, or CBRT, currently under development is based on the adaptation of a linearaccelerator (linac) to a device which allows to dynamically curve the original trajectory of the electron beam sothat it impacts upon a target. This produces a photon beam via Bremsstrahlung which converges on a pre-determined focus point (isocenter). Adaptation of the RTHC device is only possible if it is sufficiently compact, asthe device must be placed between the linac head exit and the gurney. This requires that new magnetic de-flection devices be developed. This paper describes the theoretical and experimental development of controlled-deflection electron beam systems (at energies in MeV ranges) generated in a dual linear accelerator waveguide. Adevice which follows RTHC geometry is adapted for the system, using new magnetic deflector designs based onpermanent neodymium magnets which reach magneticfield intensities in the order of Tesla. The methodologythat was developed includes calculations of the radii of curvature with relativistic considerations for mono- andpoly-energetic electrons. Deflection angles were calculated based on this theoretical foundation, using a programdeveloped in MatLab®which shows the trajectory of electrons both under ideal conditions (uniform magneticfield) and real conditions (magneticfield defined through intensity distribution). Monte Carlo simulation sub-routines were implemented in order to estimate the spectrum of electrons issuing from the linac as well as todirectly determine the electron beam trajectory with magnetic deflectors present. Theoretical and simulatedresults were compared to experiments performed with a clinical linear accelerator, demonstrating correspon-dence between different methodologies and confirming the ability to achieve electron beam deflection levelsnecessary for implementation of convergent beam radiotherapy device.

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