Dosage in Radiation Therapy

There are two distinct aspects from which the subject of dosage in radiation therapy can be regarded. The first is the physical aspect concerned with the accurate measurement of and statement of dosage. The second is the purely clinical aspect concerned with the determination of the appropriate doses required in actual clinical practice. Although such a clear distinction would seem to be obvious, and is absolutely essential to future progress, yet many of the systems of dosimetry at present in use fail to provide adequately for this distinction between the measurement of dose and the selection of appropriate dosage. This paper deals only with the first of these—namely the basic physical factors. Actually there are three such factors: (1) Quantity of radiation or dose. (2) Quality of radiation, i.e., wave-length. (3) Time of radiation or the same thing differently expressed as intensity. A complete physical description of any treatment is given if these three—dose, quality and time can be completely stated in simple terms. Any investigation into the influence of quality or of time upon therapeutic results depends to such an extent on the satisfactory determinations of dose that this must be considered first. In the development of modern medicine, the use of biological units of dosage is essentially a transient though necessary phase in the development of technique, to be succeeded by the more reliable phase of physical measurement as soon as possible.