Dosage-rate in Radiotherapy

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Abstract
Dosage-rate is defined as number of röntgens in unit time, usually röntgens per minute. In accordance with this definition the scope of this paper is limited to the significance of dosage-rate in radiotherapy, and is not concerned with the effects of fractionation of dosage as such nor the effects of spreading out the administration of a dose of radiation over a long time by fractionation, but only with the questions connected with the rate at which the radiation is delivered during actual exposure. As practical radiotherapists we are concerned with the significance of dosage-rate in its application to technique, but as scientists who must ultimately make progress in technique by the application of new knowledge of the truth we must also concern ourselves with the fundamental biological principles involved, and so I think we must ask ourselves the following questions in an attempt to ascertain the significance for us of dosage-rate. First we must ask ourselves the question: “Is there a difference in biological effect corresponding to differences in dosage-rate?” Secondly we must ask: “If there is a difference what, if any, are the critical values of dosage-rate above and below which the effects are different?” Thirdly comes the question: “How do the facts about the effects of variation of dosage-rate bear upon the practice of radiotherapy?”