Uncertainty in treatment of head-and-neck tumors by use of intraoral mouthpiece and embedded fiducials

Purpose: To reduce setup error and intrafractional movement in head-and-neck treatment, a real-time tumor tracking radiotherapy (RTRT) system was used with the aid of gold markers implanted in a mouthpiece. Methods and Materials: Three 2-mm gold markers were implanted into a mouthpiece that had been custom made for each patient before the treatment planning process. Setup errors in the conventional immobilization system using the shell (manual setup) and in the RTRT system (RTRT setup) were compared. Eight patients with pharyngeal tumors were enrolled. Results: The systematic setup errors were 1.8, 1.6, and 1.1 mm in the manual setup and 0.2, 0.3, and 0.3 mm in the RTRT setup in right-left, craniocaudal, and AP directions, respectively. Statistically significant differences were observed with respect to the variances in setup error (p <0.001). The systematic and random intrafractional errors were maintained within the ranges of 0.2-0.6 mm and 1.0-2.0 mm, respectively. The rotational systematic and random intrafractional errors were estimated to be 2.2-3.2°and 1.5-1.6°, respectively. Conclusions: The setup error and planning target volume margin can be significantly reduced using an RTRT system with a mouthpiece and three gold markers.