Comparison of repositioning accuracy of two commercially available immobilization systems for treatment of head-and-neck tumors using simulation computed tomography imaging

PURPOSE: To compare the setup accuracy, comfort level, and setup time of two immobilization systems used in head-and-neck radiotherapy. METHODS AND MATERIALS: Between February 2004 and January 2005, 21 patients undergoing radiotherapy for head-and-neck tumors were assigned to one of two immobilization devices: a standard thermoplastic head-and-shoulder mask fixed to a carbon fiber base (Type S) or a thermoplastic head mask fixed to the Accufix cantilever board equipped with the shoulder depression system. All patients underwent planning computed tomography (CT) followed by repeated control CT under simulation conditions during the course of therapy. The CT images were subsequently co-registered and setup accuracy was examined by recording displacement in the three cartesian planes at six anatomic landmarks and calculating the three-dimensional vector errors. In addition, the setup time and comfort of the two systems were compared. RESULTS: A total of 64 CT data sets were analyzed. No difference was found in the cartesian total displacement errors or total vector displacement errors between the two populations at any landmark considered. A trend was noted toward a smaller mean systemic error for the upper landmarks favoring the Accufix system. No difference was noted in the setup time or comfort level between the two systems. CONCLUSION: No significant difference in the three-dimensional setup accuracy was identified between the two immobilization systems compared. The data from this study reassure us that our technique provides accurate patient immobilization, allowing us to limit our planning target volume to <4 mm when treating head-and-neck tumors.