The magnetic confinement of electron and photon dose profiles and the possible effect of the magnetic field on relative biological effectiveness.

It has been shown experimentally that the focusing provided by a longitudinal non-uniform high magnetic field can significantly improve electron beam dose profiles. This could permit improved targeting of tumors near critical areas and minimize the radiation dose to surrounding healthy tissue. The experimental results together with Monte Carlo simulations suggest that the magnetic confinement of electron radiotherapy beams may provide an alternative to proton or heavy ion radiation therapy in some cases. In the present work, the external magnetic field capability of the Monte Carlo code PENELOPE was utilized by providing a subroutine that modeled the actual field produced by the solenoid magnet used in the experimental studies. The magnetic field in our simulation covered the region from the vacuum exit window to the phantom including surrounding air. In a longitudinal non-uniform magnetic field, it is observed that the electron dose can be focused in both the transverse and longitudinal directions. The measured dose profiles of the electron beam are generally reproduced in the Monte Carlo simulations to within a few percent in the region of interest provided that the geometry and the energy of the incident electron beam are accurately known. Comparisons for the photon beam dose profiles with and without the magnetic field are also made. The simulations also show that the electron dose profile can be manipulated by the appropriate control of the beam energy together with the strength and displacement of the longitudinal magnetic field. The potential application of high magnetic fields in radiation therapy requires investigation of the possible effect of the magnetic field on the relative biological effectiveness (RBE) of the radiation. An experimental study was done in this thesis to investigate the survival rate of a yeast cell line. The magnetic field was produced by NdFeB permanent magnets. Saccharomyces cerevisiae cells were irradiated with 60Co source with and without a transverse magnetic field. Our experiments show an indication that the survival rate decreases by a few percent and hence the RBE may be increased slightly in the presence of a 0.78 T magnetic field.Ph.D.Applied SciencesBiological SciencesBiomedical engineeringBiophysicsHealth and Environmental SciencesNuclear physicsNuclear physics and radiationOncologyPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125039/2/3186593.pd