ESTRO 2024 - Abstract Book

S4135

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2024

29 patients received 79 fractions of spine SBRT. 1006 pairs of stereoscopic X-rays were analyzed for intrafractional motion, of which 194 (19.3 %) showed at least one out-of-tolerance deviation. 135 image pairs had an out-of-tolerance deviation in only one DOF, 59 image pairs had out-of-tolerance deviations in two or more DOFs. In all 6 DOF combined, 284 out-of-tolerance deviations were recorded. Out-of-tolerance deviations occurred in all but one patient and in 62 of 79 fractions. The frequency varied between patients. Out-of-tolerance deviations were observed in all 6 DOF. Mean absolute deviations were 0.33 mm, 0.31 mm and 0.21 mm in the lateral (x), longitudinal (y), and vertical (z) directions and 0.15°, 0.18° and 0.14° for pitch (x rotation), roll (y rotation), and yaw (z rotation), respectively. Maximum translational deviations were 2.60 mm (x), 3.10 mm (y), and 2.79 mm (z). Maximum rotational deviations were 1.75° (x rot), 2.60° (y rot), and 1.79° (z rot). Translational deviations were more frequent than rotational ones. The distribution of deviations was bidirectional in all six DOF and centered around the origin. The frequency and magnitude of deviations showed an inverse relationship. The mean MCDs were 1.17 mm (x), 1.09 mm (y), 0.56 mm (z) and 0.40° (x rotation), 0.46° (y rotation), 0.39° (z rotation). The largest MCDs measured were 5.08 mm (x), 8.86 mm (y) 3.34 mm (z) and 2.06° (x rotation), 4.96° (y rotation), 2.55° (z rotation). We observed differences in the patterns of motion during treatment: Some patients tended to move back and forth, resulting in small cumulative deviations. Others tended to keep moving in the same direction, which would have resulted in large and relevant deviations without repositioning.