Analysis of emission of beta emitting radiation sources under experimental conditions in a magnetic field

Purpose: The purpose of this study is to show the deviation of beta particles emitted from beta emitting radioactive sources in the presence of magnetic field under experimental conditions. To achieve this, the change of dose range of Ytrium-90 (90Y), which is a pure beta emitter, was examined using Gafchromic EBT (External Beam Therapy) films.Material and Methods: 90Y source was placed on the experiment rig made of Plexiglas, passing through the center of the film, and kept for nearly 1 hour either in normal room conditions or in the MRI device. Then the films were scanned and color change of the films were converted into the tones of gray using Matlab. Isodose curves that refer to the tones of gray were created, and the diameters of isodose curves were measured in pixels.Results: At the distance of 0mm from the source, the change in the X direction at the inner circles of the isodose curves was found to be greater by 5% when magnetic field was applied compared to the isodose curves of the films irradiated without magnetic field. At 2mm distance from the source to the direction perpendicular to the magnetic field showed a reduction of approximately 12% compared to the change of the diameters of isodose curves of the films irradiated without magnetic field.Irradiated volume estimations of each isodose curve were made referring to the gray tones numbered between 130-180 of the films with or without magnetic field in the distance of 0 and 2mm from the source. The irradiated volumes of the isodose curves of films at 0 mm and 2 mm distance from the source, 7% and 26% reductions were found when magnetic field was applied respectively.Conclusion: The isodose curve of the films without magnetic field at the distance of 0mm from the source had a circular symmetry. The diameters of isodose curves were reduced when they got further away from the source. When magnetic field is applied, the isodose curves showed an elliptical structure. The effect of the magnetic field has increased away from the source. These findings showed that the dose gathers at the centre when magnetic field is applied. A decrease was observed in the volume when magnetic field was applied and this decrease became more pronounced away from the source.Key words: gafchromic film, magnetic field, Ytrium-90, beta emission