Aspects of radiation biology and radiation pathology observed during the treatment of cancer in man. The Mackenzie Davidson memorial lecture delivered at the British Institute of Radiology on May 16, 1974.

Abstract

1. The ‘required tumour lethal dose’ for all human cancers treated with irradiation ranges from approximately 500 rads to more than 12,000 rads. Therefore, when attempting to quantify the influence of biological factors such as hypoxia, variation in sensitivity during phases of a cell cycle, growth-rate, fractionation patterns, etc., the transposer must be reminded that these factors must exert their influence over a universe of tumours that vary in radio-sensitivity by as much as 25 to 1. It is probable that many radiobiological laws that are applicable to radio-resistant tumours may not apply to radio-sensitive tumours, and vice-versa. 2. Amongst each type of tumour, the required tumour lethal dose varies most commonly by a factor of 2, and in some tumours by much as 3½. A standard dosage formula or isoeffect curve can provide only a first approximation of the required tumour lethal dose. Serial biopsy studies plus observation of volume growth and regression-rates during and toward the end of treatment ...