Isodose Surfaces

Abstract

It is now scarcely necessary to insist upon the importance of estimating as exactly as possible the dose of radiation received by a patient during X-ray or gamma-ray treatment. Whatever complexities there may be in the biological and clinical effects of these radiations, it is certain that one of the main factors determining them is the amount of energy absorbed. No one would now deny that without a knowledge of the dose received we are lacking in the first and most fundamental of our possible information. The development of the physical aspects of this problem occurred in a series of fairly well defined stages. First came the establishment in 1928, of a unit of dose (the röntgen) for X rays, followed by its adoption nine years later for gamma rays as well. The measurement of beams of radiation in air henceforth presented few difficulties. As a next stage it was evidently of great importance to find the dose at a depth in tissues and this proved a more difficult matter. The discovery of the great importance of scatter in determining depth dose defeated the mathematician and turned the experimental determination of depth doses into an important aspect of hospital physics. At first the measurements were confined to the central axis of beams sent into “water phantoms” substituted for the patient and little further information was sought.