ESTRO 2021 Abstract Book

S1477

ESTRO 2021

Results 9 patients received a total of 34 fractions of spine SBRT. Overall, 382 intrafractional X-ray data sets were recorded, of which 53 (13.8%) showed at least one value out of tolerance with 82 values out of tolerance altogether. Body position was corrected when out of tolerance. Errors occurred in all six degrees of freedom with the most frequent being longitudinal (N=26) and lateral (N=21) translational errors. Motion occurred in both directions of each dimension with mean values consequently being close to 0 (Figure 2). Maximum absolute deviations were 1.75 mm (lateral), 2.32 mm (longitudinal), 1.43 mm (vertical), 1.24° (pitch), 2.29° (roll), and 0.99° (yaw).