A history of radiation shielding of x-ray therapy rooms.

In this report the history of shielding for radiation treatment rooms is traced from the time of the discovery of x-rays to the present. During the early part of the twentieth century the hazards from ionizing radiation were recognized and the use of lead and other materials became commonplace for shielding against x-rays. Techniques for the calculation of the shield thickness needed for x-ray protection were developed in the 1920's and shielding materials were characterized in terms of the half value layer or simple exponential factors. At the same time, better knowledge of the interaction between radiation and matter was acquired. With the development of high energy medical accelerators after 1940, new and more complex shielding problems had to be addressed. Recently, shielding requirements have become more stringent as standards for exposure of personnel and the general public have been reduced. The art of shielding of radiation treatment facilities is still being developed and the need for a revision of the reports on shielding of medical accelerators from the National Council on Radiation Protection and Measurements is emphasized in this article.