Geometric Miss with Four-Field Box Technique in Carcinoma Cervix-A Volumetric Evaluation

Abstract

In India, carcinoma cervix is still treated with the conventional four-field box technique of radiation using fluoroscopy-based planning which has got a greater chance of geometric miss. This study aims to quantitatively analyze and compare the conventional technique versus CT-based planning to assess the geometric miss in primary target volumes for external beam irradiation. A retrospective evaluation of 54 patients with carcinoma cervix of stage IIB to IVA treated with radical concurrent chemoradiation in our department from 2014 to 2016 was done. Planning CT was contoured as per the guidelines for both conventional four-field technique and 3D CRT. The volumetric difference caused by the change in the posterior border of the primary target volumes was analyzed as this is the most common site of geometric miss regarding primary disease. The volume of primary CTV ranged from 13 to 583 cc with a mean value of 179.55 cc when planned by conventional borders and from 56 to 591 cc with a mean value of 183.3 cc when planned with CT. 42.5% of patients had their primary tumor volume (CTV) and 96.2% patients had their PTV inadequately covered with the conventional posterior borders. There was no statistically significant association between the volume of geometric miss and the FIGO stage of the disease. The current definitions of the posterior border of the lateral field in conventional planning using fluoroscopy are grossly inadequate for external beam irradiation in locally advanced cervical cancers. The volumes of miss were extremely variable, and we cannot predict the extent of geographic miss based on FIGO stage of the disease. It varied on individual patient depending only on tumor anatomy. In patients undergoing conventional planning, it is safer to extend the posterior border to cover the entire sacral hollow, at least in locally advanced disease to ensure adequate target coverage.