THE EFFECT OF CARBON-FIBER INSERTS ON THE BUILDUP AND ATTENUATION OF HIGH-ENERGY PHOTON BEAMS

Background and purpose: The use of new materials in radiotherapy requi res an investigation of the effects of these materials on the relevant beam parameters. The high strength and low density of carbon fibre su ggest an excellent material for table inserts with minimal attenuation , without changing the skin sparing effect in the build-up zone. Mater ials and methods: In this paper three different carbon fibre plates an d two conventionally table top materials are studied in Co-60, 6 MV an d 23 MV photon beams. Results and conclusions: From depth dose measure ments it is clear that the dose in the build-up zone is influenced in the qualities of the beams. The mutual differences for the three carbo n plates are minimal. For Co-60 the depth of the maximum dose is decre ased by carbon from 5 to 2 mm and the surface dose is increased from 1 8 to 76%. For 6 and 23 MV the surface dose is increased from 21 to 52% and 20 to 32%, respectively, as well as the dose in the build-up regi on. A transmission of 99% was measured for two carbon plates out of th ree in Co-60 and for one out of three in 6 MV. (C) 1997 Elsevier Scien ce Ireland Ltd.