Consideration of Body Dose in Radiation Therapy

Abstract

In modem radiation therapy, we usually designate the treatment, by the dose per unit volume of the tissue we wish to radiate (relative to the per cent of erythema skin dose viz e). It is evident that a certain dose of this kind can be given in a number of different ways. The amount of radiation absorbed by the entire body or total body dose is however dependent upon what “fields” we choose for reaching the desired “tumor dose” and the general reaction of the patient. For instance, the change in the blood picture has more to do with the “total body dose” than with the “tumor dose.” We therefore consider it important to keep record of the “total body dose” as well as of the “tumor dose.” The question arises how the unit for the body dose ought to be defined and how the total dose ought to be figured. Wintz has recently published an article1 in which he calls attention to the importance of the body dose. He uses a certain unit “a.” The unit we have been using for some time is approximately 100 times smaller. I have designated it Ax and have defined it in the following way. The X -ray tube is excited by 200 kv. (measured with sphere-gap) alternating 60 cycle current with double way rectification and the rays filtered through 0.5 mm. copper and 5 mm. wood. If an erythema dose is given on the skin of a 10 × 10 cm. field then 100 Ax will be absorbed by the first 5 cm. of tissue presupposing that it is surrounded in all directions by tissue so that a very small part of the scattered radiation is lost laterally. A variation in the distance between the target and the skin does not influence the “body dose” enough to be considered as long as the whole ray cone passes entirely through the tissue. The absorption by different layers of tissue is given in Table 1.