The Ellis formulae for X rays and fast neutrons

The relationship between total dose, number of fractions (N) and over-all treatment time (T days) is of great importance in radiotherapy when any non-standard fractionation schedules are considered. The use of the formula by Ellis (1969) relating these qualities for X and γ rays, i.e. where N.S.D. = nominal standard dose), is increasing, partly because of its simplicity and partly because of the availability of a slide rule adjusted to fit its parameters (Winston, Ellis and Hall, 1969).