Photon general cavity theory

General cavity theory applied to photons is reviewed. The three general cavity expressions, that due to Burlin, the modification by Horowitz and that recently suggested by Kearsley, are compared in detail and their relative success in predicting experimental data from the landmark Ogunleye et al cobalt-60 study of the cavity effect for LiF TLDs in media of polystyrene, aluminium, copper and lead is evaluated. For moderately mismatched cavity and medium (LiF in polystyrene or aluminium) all three expressions give excellent agreement with experiment so that the Burlin expression is preferred due to its greater simplicity. The Burlin-Horowitz expression is the only one which yields satisfactory agreement with experiment for all four wall materials with a single value of the electron mass-energy fluence attenuation coefficient. The Kearsley expression is the only one capable of yielding cavity dose distributions, but requires further experimental and theoretical development due to the relatively large number of unknown parameters it employs. (author)