Inter- and intraobserver variation in HR-CTV contouring: Intercomparison of transverse and paratransverse image orientation in 3D-MRI assisted cervix cancer brachytherapy

Aim: To analyze agreement between target volumes, delineated by two observers on transverse (T) and paratransverse (perpendicular to the long cervical axis - PT) MR images for cervix cancer brachytherapy. Materials and methods: In 13 patients, High Risk-CTV (HR-CTV) was outlined by two observers in T and PT MR image plane, respecting the GYN GEC-ESTRO recommendations for 3D-image based cervix cancer brachytherapy [1]. Contouring time was measured. HR-CTV sizes were compared, and conformity index (CI) was assessed. Interobserver variations in contour-extent along eight radial directions were compared between delineation planes. After applying a standard treatment plan, an intercomparison of DVH-parameters V100, D90, and D100 for the HR-CTV was carried out. Results: Contouring time was slightly longer in T than PT orientation. Interplane Cl did not differ significantly between observers (0.72 vs. 0.71), nor did the interobserver CI between planes (0.79 vs. 0.78). Variations in contour-extent between different radial directions and interplane deviations in DVH parameters were non-significant. Conclusion: Contouring in PT, as compared to T plane, allows for a "circumferential view of the cervix" and facilitates comprehensive understanding of spatial relations between the applicator and patho-anatomical structures. It is marked by a lower contouring difficulty and leads to a comparable outcome in terms of DVH parameters. Interobserver inconsistencies can be minimized by systematic training and following the published recommendations. (c) 2008 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 89 (2008) 164-171.