Cumulative radiation effect part I: Fractionated treatment regimes

Abstract

The object of this paper is to establish a criterion as a basis on which to assess the biological effect of the widely varied fractionated regimes at present used in the radiotherapy of malignant diseases. These assessments are based on a scale of the accumulated sub-tolerance radiation damage, the Cumulative Radiation Effect (CRE). The CRE is a generalised form of the empirical function (NSD) for the assessment of damage at tolerance, which has been described by Ellis. The properties of the CRE function are examined in some detail, and its application to various clinical situations described and illustrated by numerical examples. The CRE can be considered as a summation of the effects of fractions or groups of fractions, but these effects cannot be evaluated without consideration of the amount of damage caused by previous fractions. To take previous damage into account, the equivalence conditions existing at the junctions between fractions or schedules must be determined. It is found that if a particular regime achieves a certain CRE, its individual fractions may be given in any order whatsoever, without altering the CRE attained.