Effect of Transverse Magnetic Field on Build-up Region of 6 MV Photon Beam

The purpose of this study was to present an improved method of dose modulation over the increase of build-up for existing 6MV photon beam. Two neodymium permanent magnets with a strength of 0.5 T (Tesla) were applied with a magnetic field perpendicular to the photon beam. The effects of dose on build-up region with or without the magnetic field were measured according to the magnet-to- magnet distance (MMS) and the magnet-to-surface distance (MSD). For MMS = 6 cm and MSD = 2.5 cm, D-0mm, D-2 mm, D-5 (mm), and D-10 (mm) showed improved doses of 6.8 %, 14.6 %, 6.9 %, and 2.1 %, respectively, as compared with 6MV open beam. In this study, the device with low strength magnetic field can be applied directly to the outside of the human body when the target volume located close to the skin is delivered with radiation. It is expected that the method of build-up modulation using a low strength magnetic field will be feasible in the clinical applications.