MAJOR GEOMETRIC VARIATIONS BETWEEN MULTIPLE HIGH-DOSE-RATE APPLICATIONS OF BRACHYTHERAPY IN CANCER OF THE CERVIX - FREQUENCY AND TYPES OF VARIATION

PURPOSE: To evaluate major geometric variations in multiple intracavit ary applications for carcinoma of the cervix. MATERIALS AND METHODS: O rthogonal radiographs were reviewed of 17 consecutive patients with ca rcinoma of the cervix treated with 70 applications of high-dose-rate b rachytherapy. In seven patients, conscious sedation was used for all a pplications. In 10 patients, general anesthesia was used for the first application and conscious sedation for subsequent applications. Major geometric variation between applications in axis, length, and slippag e in tandem placement and separation, packing, and slippage in colpost ats placement were reviewed. A major variation was defined as more tha n 1.0-cm deviation. RESULTS: Major variations between applications occ urred more commonly in colpostats placement than ih tandem placement. For tandems, the rates of variation were 5.7% in axis, 4.3% in length, and 1.4% in slippage. For colpostats, rates of variation were 7.1% in separation, 25.7% in vaginal packing, and 7.1% in slippage. No consis tent pattern of variation was found between applications except in vag inal packing. CONCLUSION: Awareness of geometric variations should imp rove proper placement of intracavitary applicators for brachytherapy.