“…Several authors, including Zhuang et al 19 9 reported tracking errors of 0.9 mm (mean), 0.5 mm (1 SD), 2.7 mm (max), and RMS error of 1.0 mm. Our differences between tracking software and manual scoring of tumor position (validation data) were 1.1 mm (mean), 0.5 mm (1 SD), 2.5 mm (maximum), with a RMS of 1.2 mm (case A) and 0.7 mm (mean), 0.5 mm (1 SD), 1.7 mm (maximum), and a RMS of 0.3 mm (case B, in the two selected segments where tracking was possible).…”