Localization of the apex of the vagina: Implications for radiation therapy planning

PURPOSE: To evaluate (a) the displacement of the vaginal apex by a rod during radiation therapy simulation for gynecologic malignancy and (b) apical localization with implanted radiopaque markers. MATERIALS AND METHODS: Metallic markers were implanted in the cervix or vaginal cuff in nine patients with cervical or endometrial carcinoma who underwent irradiation. In all but one patient, radiographs were obtained with and then without the vaginal rod. Displacement of the markers relative to bone landmarks was measured. The total displacement was the square root of the sum of the squares of displacement in each axial direction. RESULTS: All patients showed displacement of the cervical markers by the vaginal rod (mean total displacement, 1.9 cm; range, 0.6-3.6 cm). The greatest displacement was cephalic (mean, 1.5 cm; range, 0.5-2.4 cm). Anteroposterior displacement occurred in all patients but was not as predictable as cephalic displacement. Displacement was anterior in five of the eight patients, posterior in three patients, and lateral in four patients. CONCLSUION: Displacement of the vaginal apex and/or cervix with placement of the vaginal rod during simulation was marked in all patients. Use of implanted cervical markers to localize the vaginal apex or the cervix during stimulation is more accurate than use of a vaginal rod.