Absorbed dose distribution of electron beams in uniform and inhomogeneous media.

The absorbed dose at dose maximum in different materials or tissues irradiated by a given electron fluence can vary considerably depending on scattering and stopping properties of the media. A simple expression relating the dose levels in different materials have been derived and is found to be in good agreement with published experimental results for different phantom materials. This expression has been used to calculate the ratio of the absorbed dose to different tissues to that in water. The absorbed dose behind different inhomogeneities has been investigated experimentally. Based on this expression correction factors and scaling laws have been derived which allow the calculation of the absorbed dose distribution behind the inhomogeneity with good accuracy. The procedure only uses tabulated mass scattering and total stopping power data and the dose distribution in the uniform medium. The shift in penetration behind the inhomogeneity independent of its depth is shown to be accurately determined by the equivalent thickness of the inhomogeneity as obtained by multiplying the real thickness by the total stopping power ratio at the incident mean energy.