Application of cavity theories for electrons to the derivation of absorbed dose conversion factor Csub(E)

The cavity theories of Burlin et al., Almond and McCray, Holt et al., and Fregene for electron beams have been used to obtain values of absorbed dose conversion factor Csub(E) for high energy electrons, using a general expression for an air walled ionization thimble chamber. All four theories yield consistent values of Csub(E) except for Burlin et al.'s at low energies. Values obtained from Holt et al.'s and Fregene's expressions are very much in agreement with those already presented by ICRU and Nahum and Greening. With appropriate conditions previous expressions for Csub(E) could be obtained from at least one of the theories. (author)