Clinical Tumor Dimensions May Be Useful to Prevent Geographic Miss in Conventional Radiotherapy of Uterine Cervix Cancer—A Magnetic Resonance Imaging–Based Study

Purpose To evaluate the risk of geographic miss associated with the classic four-field “box” irradiation technique and to define the variables that predict this risk. Materials and Methods The study population consisted of 80 patients with uterine cervix cancer seen between 2001 and 2006. Median age was 55 years (23–82 years), and 72 (90%) presented with squamous cell carcinoma. Most patients (68.7%) presented with locally advanced disease (IIb or more). Magnetic resonance imaging findings from before treatment were compared with findings from simulation of the conventional four-field “box” technique done with rectal contrast. Study variables included tumor volume; involvement of vagina, parametrium, bladder, or rectum; posterior displacement of the anterior rectal wall; and tumor anteroposterior diameter (APD). Margins were considered adequate when the target volume (primary tumor extension, whole uterine body, and parametrium) was included within the field limits and were at least 1 cm in width. Results Field limits were inadequate in 45 (56%) patients: 29 (36%) patients at the anterior and 28 (35%) at the posterior border of the lateral fields. Of these, 12 patients had both anterior and posterior miss, and this risk was observed in all stages of the disease ( p = 0.076). Posterior displacement of the anterior rectal wall beyond S2-S3 was significantly correlated with the risk of geographic miss ( p = 0.043). Larger tumors (APD 6 cm or above and volume above 50 cm3 ) were also significantly correlated with this risk ( p = 0.004 and p = 0.046, respectively). Conclusions Posterior displacement of the anterior rectal wall, tumor APD, and volume can be used as guidance in evaluating the risk of geographic miss.