Radioactive Gold for the Intracavitary Treatment of Carcinoma of the Cervix

The purpose of this paper is to describe an attempt to increase the dose of radiation delivered to the parametria for the treatment of carcinoma of the cervix. The generally accepted method of radiation therapy for carcinoma of the cervix consists in combining the radiation from a series of intrauterine and vaginal radium sources with external irradiation of the lateral pelvis. While this method delivers an adequate dose of radiation to the local lesion, the dose to the parametrial tissues is frequently insufficient to control cancer in that area. In the attempt to raise the parametrial dose of radiation to a cancerocidal level, excessive irradiation and injury to the rectum, the bladder, and the paracervical triangles may occur. The vast amount of accumulated clinical experience places the tolerance of the rectum and the bladder in the neighborhood of 6,000 r and that of the paracervical triangles at approximately 9,000 r, when the irradiation is protracted over a period of about four weeks. The radiation tolerance of the cervix and the vaginal mucosa are considerably higher, probably of the order of 20,000 r. Consequently they do not represent a serious limitation to the amount of radium which can be placed in the vagina. Furthermore, the radiation-sensitive organs lie anterior and posterior, and above the vagina. Most conventional technics of radium therapy exploit this situation by placing the vaginal radium applicator in the lateral fornices as far as possible from the midline by distending the vagina laterally. This increases the distance between the radium sources and the rectum and bladder and brings the radium closer to the node-bearing areas. The radiation thus delivered is usually supplemented by the contribution of a series of radium sources placed in the uterine canal. Keeping within tolerance of the normal structures, such a distribution of radium applied under the best anatomical circumstances, i.e., a large distensible vagina, will deliver a maximum of approximately 3,000 r to the Manchester point “B” (1, 2). Another possible approach to the problem of protecting the bladder and rectum was investigated by Neary (3), who developed a radium applicator suitably shielded to cast a desirable protective shadow. Unfortunately, the high energy of the radiation emitted by radium requires a rather thick shield even of the heaviest metal. As a result, it is necessary to use a bulky applicator which fits only the roomiest vaginas, thus restricting the versatility of the instrument. It seemed reasonable, therefore, to explore the possibility of replacing the radium by a radioactive element emitting a lower energy radiation requiring less heavy shielding. This suggestion was mentioned by Neary and studied by Tudway (4).