Contouring of the Pharyngeal Superior Constrictor Muscle (PSCM). A cooperative study of the Italian Association of Radiation Oncology (AIRO) Head and Neck Group

Background and purpose: Irradiation of the Pharyngeal Superior Constrictor Muscle (PSCM) seems to play a crucial role in radiation-related swallowing dysfunctions. Purpose of our study was to quantify operator-related variability in the contouring of PSCM on Computed Tomography (CT) scans and adherence with contours derived from MR images. Materials and methods: Three sets of treatment planning CT and their corresponding MR images were selected. Contouring of the PSCM was performed using both a literature-based method, derived from literature review, and an optimized method, derived from Magnetic Resonance (MR) images thus obtaining ‘‘literature-based’’ and ‘‘optimized’’ contours. Each operator contoured the PSCM on CT scans according to both methods for three times in three different days. Inter- and intra-operator variability and adherence to a contour obtained from MR images (named ‘‘MR-derived’’ contour) were analyzed. Results: Thirty-four operators participated and 612 contours were obtained. Both intra- and inter-operator variability and adherence to the ‘‘MR-derived’’ contour were significantly different between the two methods (p 6 0.05). The ‘‘optimized’’ method showed a lower intra- and inter-operator variability and a higher adherence to the ‘‘MR-derived’’ contour. Conclusions: The ‘‘optimized’’ method ameliorates both operator-related variability and adherence with MR images.