The density scaling theorem applied to lateral electronic equilibrium.

Some theoretical considerations concerning the application of the density scaling theorem to secondary electrons from high-energy x-ray beams are discussed. It is concluded that the theorem is expected to be applicable with acceptable accuracy for 10-MV x-ray beams in low-density materials. Measurements reported by different groups of workers are discussed and shown to be in general agreement with the theorem, with one exception. It is shown that the theorem can be applied in combination with phantom scattering correction factors to calculate the dose in homogeneous bodies which differ from water in their density. The method of calculation is similar to the equivalent tissue-air ratio method, but takes account of the effects of loss of lateral electronic equilibrium.