Accuracy of surface-guided radiotherapy-based positioning and surface tracking in breast radiotherapy using a...

This study aimed to evaluate the accuracy of surface-guided radiotherapy (SGRT)-based positioning and surface tracking in breast radiotherapy using the ExacTrac Dynamic (ETD). We retrospectively evaluated 16 patients who underwent breast cancer treatment. All patients were positioned using SGRT with ETD under free-breathing conditions. Orthogonal kilovoltage (kV) image acquisition was then acquired using the linear accelerators' kV imagers and registered to digitally reconstructed radiographs. For surface tracking, vertical breast surface motion waveforms obtained with ETD were compared with those captured using an electronic portal imaging device (EPID) during beam delivery. The agreement between ETD and EPID in terms of vertical breast surface displacement was evaluated using the cross-correlation coefficient. For patient positioning, the mean ± standard deviation (SD) of X-ray shift values (mm) were - 2.8 ± 2.6 (vertical), - 2.2 ± 4.5 (longitudinal), and 0.3 ± 2.1(lateral). The percentage of X-ray shift < 5 mm was 82% (vertical), 66% (longitudinal), and 92% (lateral). The setup margins (mm) were 5.4 (vertical), 9.0 (longitudinal), and 3.8 (lateral). For surface tracking, the mean ± SD of the cross-correlation coefficient was 0.93 ± 0.02, indicating a high correlation between the ETD and EPID waveforms. The mean amplitude difference between waveforms obtained by ETD and EPID was 0.46 mm. SGRT-based positioning with ETD may result in errors exceeding 5 mm relative to the treatment planning position in the longitudinal direction; combining it with image-guided radiotherapy is therefore recommended. Surface tracking with ETD demonstrated high tracking accuracy in tracking human body surface temperature distribution.