It has been shown that the curative dose (D) for mammary cancer treated with a given number of daily fractions (T) can be expressed by an “iso-effect” formula D = ETn, similar to that derived for other tissues. Estimates of the parameters E and n obtained from published data and independently from 60 personally observed cases are in good agreement. It is found that mammary carcinoma (E = 1250 r, single exposure) is materially more radio-sensitive than epidermoid cancer, and that the recovery exponent (n = 0·34) is similar to that of normal skin. In the case of breast cancer, therefore, it is not possible to improve the therapeutic ratio by prolonged daily fractionation, and since the treated area is necessarily large it is essential to deliver homogeneously doses of radiation approaching the limits of skin tolerance. It is thought possible that another fractionation procedure, with longer intervals between treatments, may give a more favourable therapeutic ratio, but from the present analysis there appears to be no theoretical advantage in protracting treatment for this disease.
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Lionel Cohen (1952) studied this question.