Use of Beam Spoiler to Improve Build-up of Photon Beam Using Low Strength Magnetic Field

Abstract

The purpose of this study is to propose the use of a beam spoiler for improving the build-up region of photon beam by using external magnetic field with a low strength of 0.5 T (Tesla) outside the human body. A homemade magnet device which can apply a transverse magnetic field to photon beam was developed. The effect of dose enhancement on build-up region was investigated by the beam spoiler-to-magnet distance (BMD), the magnet-to-magnet distance (MMD), and the magnet-to-surface distance (MSD). Build-up regions of 6 MV photon beam with and without the magnetic field were measured for the field size to 5 × 5 ㎠. When applying the low magnetic field with MMD of 10 cm, D<SUB>0mm</SUB>, D<SUB>2mm</SUB>, D<SUB>5mm</SUB> and D<SUB>10mm</SUB> at BSD of 13 cm and MSD of 5 cm were increased by approximately 3.2%, 3.9%, 1.7% and 0.4%, respectively, compared to the build-up of the existing 6 MV photon beam without the magnetic field. The dose reduction was 5.1% compared to skin dose for 4 MV photon beam without the magnetic field. It is expected that use of a beam spoiler in the magnet device designed in this study could provide improved dose distributions in build-up regions while maintain similar surface dose to the existing 6 MV photon beam without the magnetic field.