Energy Absorption. II. Part I—Integral Dose when the Whole Body is Irradiated

Abstract

Some four years ago experimental and theoretical investigations (Mayneord, 1940) were commenced on the absorption of energy during X-ray and radium treatment. It was emphasised that the total energy absorbed throughout the body is a quantity of great physical and clinical importance, and our own intervening experience (Mayneord, 1942, 1943), as well as the work of other investigators (Happey, 1940, 1941; Ellis, 1942; Bush, 1943; Hilton, 1943; Smithers, 1942), has developed this conclusion. As a first approximation to a unit of “integral dose”, that is, total absorption throughout a given mass of tissues, we have suggested (Mayneord, 1940) 1 gramme-röntgen. This quantity is the energy conversion when 1 r is delivered to 1 gm. of air, and is approximately equal to 85 ergs. For clinical use this unit is too small, but 1 megagramme-röntgen (one million gramme-röntgens) proves to be of a convenient order of magnitude and has been generally adopted. One megagrammeröntgen is equivalent to approximately 2 gm. calories. The present paper is the first of a series describing more detailed studies of integral dose throughout a “patient” during both therapeutic and diagnostic procedures. Some account of the mathematical theory of integral dose will be given in another paper. The amount of energy absorbed during an X-ray treatment may be estimated by various methods, all of which consist essentially in finding the volumes or masses of tissue raised to known dosage levels.