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EQUIVALENT DOSE
EQUIVALENT DOSE
A biologic-dose-equivalent number is useful, as the total dose of radiation is dependent on the manner it is administered. This biologic-dose-equivalent number compares different fractionation patterns. It was developed when patches of skin were exposed to different courses of radiation and the degree of short-term (acute) damage produced posttreatment was used to define equivalent doses. From these experiments it was realized that as a treatment regimen lengthened in time, the larger the numerical total
dose needed to be in order to produce an equivalent reaction.17
As demonstrated in the formula below, the nominal standard dose (NSD) can be related to the total numerical dose (D), number of fractions (N), and total time of a radiation course (T):