Figure 37-4

Figure 37.4. (A) External beam radiation therapy (teletherapy) is usually delivered to the pelvis through anterior and posterior portals covering the area outlined. Pelvic lymph nodes, parametria, cervix, uterus, and upper vagina are incorporated in this port. (B) Intracavitary Flecher-Suit applicator system. Intracavitary radiation therapy (brachytherapy) is usually given by placing cesium in an intrauterine tandem and contracervical applicators. The cesium sources are placed in a tandem fashion in the uterus, and a single source of cesium is placed in each vaginal applicator. The isodose curve from this application is depicted as three concentric lines. The dose to various pelvic sites is calculated (dosimetry) and depends on the strength of the cesium sources placed, the amount of time the sources remain in place, and the distance from the sources to the tissue in question. Two arbitrary points are usually calculated. Point A is found 2 cm cephalad and 2 cm lateral from the external cervical os. This point is where the ureter crosses underneath the uterine artery. Point B, which is 3 cm more lateral to point A, represents approximately the pelvic sidewall and pelvic lymph nodes. (Reprinted with permission from Clarke-Pearson D, Dawood Y. Green's Gynecology, 4th Ed. Little, Brown, Boston, 1990.)