MAGNETIC REPULSION OF LINEAR-ACCELERATOR CONTAMINATES

Neodymium Iron Boron (NdFeB) rare earth permanent magnets have unique properties that enable them to fit easily onto the accessory mount of a clinical linear accelerator to partially sweep away electron contami nation produced by the treatment head and block trays and thus increas e skin sparing. Using such magnets the central axis entrance surface d ose has been reduced by 11% for a 20x30 cm field size from 32% to 21% of maximum dose by the magnetic device. A reduction of 14% from 32% to 18% was seen for a 20x20 cm field size with a 6 mm perspex block tray positioned above the magnet. The magnetic device is light weight and thus clinically usable. (C) 1996 American Association of Physicists in Medicine.