The effect of carbon fiber couch inserts on surface dose with beam size variation.

There is little evidence in the literature regarding the effects of a carbon fiber insert on beam parameters with beam size variations. We demonstrated this effect and noted the magnitude of the change of surface dose induced. It was shown that use of the carbon fiber insert panel, despite providing minimal attenuation of the primary radiation, significantly decreased the skin-sparing effect. The magnitude of this decrease was relatively larger for smaller beam sizes. The surface dose was nearly 4 times as large when carbon was added to a 10 x 10-cm beam, and nearly double for a 40 x 40-cm beam.