High-risk clinical target volume delineation in CT-guided cervical cancer brachytherapy: Impact of information from FIGO stage with or without systematic inclusion of 3D documentation of clinical gynecological examination

Abstract

Purpose. The aim of the study was to improve computed tomography (CT)-based high-risk clinical target volume (HR CTV) delineation protocols for cervix cancer patients, in settings without any access to magnetic resonance imaging (MRI) at the time of brachytherapy. Therefore the value of a systematic integration of comprehensive three-dimensional (3D) documentation of repetitive gynecological examination for CT-based HR CTV delineation protocols, in addition to information from FIGO staging, was investigated. In addition to a comparison between reference MRI contours and two different CT-based contouring methods (using complementary information from FIGO staging with or without additional 3D clinical drawings), the use of standardized uterine heights was also investigated. Material and methods. Thirty-five cervix cancer patients with CT- and MR-images and 3D clinical drawings at time of diagnosis and brachytherapy were included. HR CTV_stage was based on CT information and FIGO stage. HR CTV_{stage + 3Dclin} was contoured on CT using FIGO stage and 3D clinical drawing. Standardized HR CTV heights were: 1/1, 2/3 and 1/2 of uterine height. MRI-based HR CTV was delineated independently. Resulting widths, thicknesses, heights, and volumes of HR CTV_stage, HR CTV_{stage + 3Dclin} and MRI-based HR CTV contours were compared. Results. The overall normalized volume ratios (mean± SD of CT/MRI_ref volume) of HR CTV_stage and HR _{stage + 3Dclin} were 2.6 (± 0.6) and 2.1 (± 0.4) for 1/1 and 2.3 (± 0.5) and 1.8 (± 0.4), for 2/3, and 1.9 (± 0.5) and 1.5 (± 0.3), for 1/2 of uterine height. The mean normalized widths were 1.5 ± 0.2 and 1.2 ± 0.2 for HR CTV_stage and HR CTV_{stage + 3Dclin}, respectively (p < 0.05). The mean normalized heights for HR CTV_stage and HR CTV_{stage + 3Dclin} were both 1.7 ± 0.4 for 1/1 (p < 0.05.), 1.3 ± 0.3 for 2/3 (p < 0.05) and 1.1 ± 0.3 for 1/2 of uterine height. Conclusion. CT-based HR CTV contouring based on FIGO stage alone leads to large overestimation of width and volume. Target delineation accuracy can systematically improve through incorporation of additional information from comprehensive 3D documentation of repetitive gynecological examination in the contouring protocol, and thus help to improve the accuracy of dose optimization in settings with limited access to imaging facilities at the time of brachytherapy. If CT information is only available, minimum 2/3 of uterine height may be a good surrogate for the height of HR CTV.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

This work was supported by the Austrian Science Fund (FWF), project L562-B19 and by the Austrian Federal Ministry of Economy, Family and Youth, and the National Foundation for Research, Technology and Development is gratefully acknowledged. The Department of Radiotherapy at the Medical University of Vienna receives financial and/or equipment support for research and educational purposes from Nucletron B.V. and Varian Medical Systems, Inc. C. Kirisits is a consultant to Nucletron, an Elekta company.