The Value of Assessing and Prescribing Dosage in Radiation Therapy in Simple Terms

Abstract

THE evolution of radiotherapy has been so rapid that progress is now being hindered by methods of prescribing and of reporting dosage which are obsolete, and should be discarded. In the earlier stages, really accurate knowledge of that one essential, the amount of radiation absorbed, was lacking, and for years it was necessary to define technic by describing in detail all the variable factors. During the transition period such details could not be omitted, but I feel that they now confuse rather than assist clear thinking. If comparison of method is to be worth while, and further progress is to be made, all the variables must be summated into a statement which gives only the essential primary factors. These I believe to be: (1) Dose, or quantity of radiation absorbed; (2) Quality, or wave length of radiation, and (3) Time, or duration of treatment. Adequately expressed, these three factors give all the necessary information. The second factor, quality, must always be described separately, and there are recognized methods of measuring wave length which I do not intend to discuss here. The first and third factors are so closely connected that they cannot be separated. Therefore, although this article deals with the first and more important—dosage—certain comments concerning the time factor are necessarily included. A paper such as this is an expression of personal opinion, and as such may appear to be dogmatic. I am well aware that controversial issues are being ignored, but it is worth an effort to go straight through the difficulties to what I believe to be the fundamental facts regarding the dose absorbed. I am, therefore, sub-dividing and dealing in the first section with: (1) General principles relating to all forms of radiation; (2) X-ray dosage, and (3) Radium dosage. In the second section, at the risk of appearing over-critical, I am enumerating under the following headings certain methods of recording dosage which I believe should be discarded: (4) Roentgens in air; (5) Erythema dose; (6) Summated roentgens to skin fields; (7) Ergs and I-Mc; (8) Radium erythema dose; (9) Millicurie-hours, and millicuries destroyed. Finally, as Section 10, I will try to illustrate the value of what I believe to be the most satisfactory method of prescribing and recording dosage of radiation. (1) General Principles.—The essential features of any valid method of dosage computation include as a first necessity the possibility of expressing the dose in terms of amount of radiation without reference to the changes produced. When a drug is under consideration, a dose is a quantity, not an effect; thereafter, the various effects are studied in relation to variation of dosage. Inevitably, because it has already gained international acceptance, that quantity in radiation therapy has to be given in roentgens. The roentgen itself is a simple physical concept of an amount of radiation, about which there is little argument.