Direct measurements and isodose calculations in radium therapy of carcinoma of the cervix.

Abstract

Until recently, radium treatment of carcinoma of the cervix was prescribed in terms of milligram hours. Although such a designation is meaningless on radiobiological grounds, considerable experience has been acquired to guide treatments on a clinical basis. The amount and distribution of radium, both for the uterine tandem and the vaginal applicators, were empirically established by the pioneer Radium Centers. Through the years, cure rates improved and radiation damage decreased. Better results and less damage could still be obtained, however, by the same well developed technics, with a knowledge of the energy absorbed at the various points in the pelvis. The total amount and distribution of radium in the uterine tandem and vaginal applicators and the shape and design of the applicators might be changed to advantage. Without a knowledge of the radiation volume distribution, any change from a technic established on clinical experience is likely to become an almost entirely new technic, since a new applicator, changing the geometrical relationship of the radium sources, modifies the distance between the radium and the mucous membrane, rectum, and bladder. The number of milligram hours suitable for an established procedure may not be appropriate for a new system. Scientific radium therapy of carcinoma of the cervix must be based on a knowledge of the volume distribution of the dose within the pelvis, with a view to (1) designing applicators producing the largest possible volume of adequate radiation in each of the common directions of spread of the disease, namely, the uterine body, parametria, and perivaginal tissues; (2) determining the doses tolerable for vital organs such as the bladder and rectum, the sites of most of the serious complications. It must, however, be kept in mind that the results obtained in the best Radium Centers without the help of dosimetry, and based only on long clinical experience of the individual radiotherapist, have yet to be surpassed. It would be decidedly a retrograde movement to accept the tagging of physical data to various points of the pelvis as replacing individual clinical experience and skill in the handling of radium. Flexibility and adaptability of the radium system to the anatomy and type of disease encountered should not be sacrificed in the interest of easier dosimetric procedures, the accuracy of which is often more apparent than real. Dosimetry gives a base line, helps the new generation of radiotherapists and gynecological therapists to understand the experience of the past, and is a working tool in the use of radium with safety and to its maximum advantage. An exaggerated emphasis on figures and a complacent regard for well filled forms where gamma roentgens appear cannot compensate for the inexperience of the therapist. Better physics and greater accuracy in physical measurements are a necessary trend if associated with extensive clinical experience of the disease and skill in the details of technic.