Investigation of the effects of a carbon-fiber tabletop on the surface dose and attenuation dose for megavoltage photon beams

Background: multiple beams are generally used with an increased possibility thatthe beam axis intersects the treatment table. treatment tabletops are commonlymade of carbon fiber due to its high mechanical strength and rigidity, low specificdensity, extremely light and low radiation beam atienuation properties. purpose ofthis paper is investigated the dose changes in the buildup region and beamatienuation by a carbon fiber tabletop for high energy 6- and 18-mv photon beams.materials and methods: measurements were performed for 10 cm × 10 cm and20 cm × 20 cm field sizes. the surface dose and percentage depth doses (%dd)were measured by a markus parallel plate chamber at a source-surface distance(ssd) of 100 cm for 6 mv and 18 mv photon beams. atienuation measurementswere made at the solid-water phantom for gantry angles of 0o and 180o rotation ofthe beam. results: a carbon fiber tabletop increases the surface dose from12.87% to 86.65% for 10 cm x 10 cm and from 8.72% to 71.16% for 20 cm ×20 cm field at 6 and 18 mv, respectively. the surface dose with the carbonfiber tabletop in an open field (0o) increases with field size. conclusion: thecarbon fiber tabletop causes a substantially increased surface dose, and alsosignificantly decreases the skin-sparing effect, which is clinically important. thedosimetric effect of the tabletop may be higher, especially for the intensitymodulatedradiation therapy depending on the beam orientation.