A method for calculating megavoltage x-ray dose and dose parameters

Limitations of the most commonly used dose calculation methodologies as apply to medium and high-energy x rays are discussed. A method is presented whereby the dose to a point in medium is divided into several components with expressions given for various components. The depth of transient-charged particle equilibrium is chosen as the reference point. Equations are derived for calculating and relating the dose parameters including the percent depth dose, the tissue-reference ratio, and the scatter-reference ratio. Particular emphasis is placed on the accuracy and adequacy of the technique in the region of buildup. The applicability of the present method to megavoltage photons is established for a number of x-ray beams in the range 4-45 MeV maximum energy.