Effect of air gap on absorbed dose in tissue.

The effect of air spaces on absorbed dose was studied, using thermoluminescent dosimeters (TLD). It was determined that, for cobalt-60 gamma rays, distances of 12 cm or more from the scattering materials were adequate to preserve skin sparing. Also, internal body cavities with dimensions greater than 4 cm in the direction of the beam would experience a reduced dose on the distal surface of the cavities.