Fractionation sensitivity and the oxygen effect

Many normal tissues in natural conditions exhibit slight radiobiological hypoxia (Hendry, 1979). Examples of this in man, which necessitated reductions in dose when the oxygenation status of the tissue was increased, are the skin (van den Brenk et al, 1965), the spinal cord (Coy & Dolman, 1971) and laryngeal cartilage (Churchill-Davidson, 1968; Henk et al, 1977). The expected effect of oxygenation status on fractionation sensitivity has not yet been considered in detail. Fractionation sensitivity can be quantified by the ratio of the parameters α and β in the following equation, which describes the probability (P) of a given level of radiation injury in a tissue following a schedule of doses (x) delivered to a total dose (D). where K is the number of tissue-rescuing units (TRU) (Hendry & Thames, 1986).