A Discussion of the Methods Used for Measuring Roentgen-Ray Applied Intensity

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Ever since roentgen rays and radium were discovered, there has been dissatisfaction with the methods which have been proposed or employed for measuring their intensity. Since the inaccuracies of each of these methods have been discussed in the literature, every radiologist should know that the chemical and biological as well as the mechanical methods cannot be depended upon in measuring the intensity or quality of radiation, or what has been commonly called “dosage.”

When the roentgen rays became generally employed in the treatment of disease, it was found that there is a limit to the amount of radiation which can be applied to the human skin without causing undesirable sequelae. This limitation, manifested by various degrees of redness or tanning, was called the “erythema reaction.” It is unfortunate that this reaction of the skin has been retained as a biological standard of dosage in therapy, and that we still try to employ it to determine the effects of radiation, and visualize it to limit treatments. Erythema means only redness. The term in no way explains the effects of radiation on pathological lesions. The degree of redness depends upon many factors such as the acuity of color vision of the observer, the interval of time elapsing between the administration and observation, the complexion and age of the patient, the ability of the vascular system to react, the volume and characteristic structure of the subcutaneous tissues which are irradiated, to say nothing of physical factors, such as the quality of the rays.