The Spencer-Attix and the Burch cavity ionization theories, both of which take into account delta-track phenomena, should, since they are not identical in form, be logically equivalent. An attempt is made to derive the basic Spencer-Attix equation using Burch''s definitions and notation. Differences between the two theories emerge which are shown to arise from approximations in the Spencer-Attix treatment. The effect of electron scattering in "small" as opposed to "infinitesimal" cavities is analysed. It is suggested that there is no rigorous theory available which can readily relate in numerical terms the ionization of gas in a cavity to the radiation energy dissipation in the surrounding wall.