Physical considerations in the design of facilities for the uniform whole-body irradiation of man.

Abstract

Whole-body irradiation is currently being applied to man for several therapeutic purposes: the destruction of bone marrow as a preliminary to autologous (1), isologous (2), or homologous (3) bonemarrow grafting in the treatment of acute leukemia; the treatment of extensive radiosensitive malignant disease, such as lymphosarcoma, Hodgkin's disease, and seminoma (4), with or without subsequent autologous bone-marrow grafts; and suppression of the immune reaction, with or without subsequent homologous bonemarrow grafting (5), to permit homografting of other tissues. It is generally considered that for these purposes a “uniform” whole-body dose should be delivered. This specification introduces two physical problems, namely the design of treatment facihties to administer a uniform whole-body irradiation dose and the evaluation of that dose. These problems are interlinked, since one must define the term radiation dose and consider the factors affecting its variationthroughout the body before an arrangement for uniform whole-body dose can be specified. 1. The Specification of Dose The words “uniform” and “dose” may each be interpreted in several ways. In whole-body irradiation procedures there has been no agreement on their meaning. Only rarely has “uniformity” in any sensebeen specified. Yet careful specification of these terms is necessary for reproducibility of scientific work or clinical treatment. Three varieties of “dose” are in use. “Air” Exposure Dose: Doses in wholebody treatments, whether in man or animals, have usually been specified as the exposure dose measured in roentgens in free air at some reference point. The twocommon points are the skin proximal to the radiation source and the midplane of the body. The variation of this air dose over the treatment zone may be cited. Such a simple specification has relatively little meaning by itself. The exposure doses measured in roentgens at points on or in a body are, of course, considerably different from those measured in free air. In particular, both the quality of the radiation and the thickness and length of the body affect the “tissue” dose received from a given “air” dose. “Tissue” Exposure Dose: I t is more desirable to specify dose as the exposure dose measured in the body in roentgens. I t is possible to specify the variation of exposure dose throughout the body, for example by citing an average dose and the per cent limits of variation.