Room: AAPM ePoster Library
Purpose: Spine stereotactic body radiotherapy (SBRT) requires minimization of intra-fractional motion; even a slight shift in position can have a significant impact on the radiation exposure sustained by the spinal cord dose. Spine SBRT typically includes prolonged treatment times, and as such, intra-fractional motion may increase. This study aimed to evaluate intra-fractional motion in spine SBRT using cone beam computed tomography (CBCT).
Methods: Four hundred and fifty-four(414) CBCT images were analyzed from 118 patients treated with SBRT with intensity modulated radiation therapy (IMRT) for spine metastases. To optimize accuracy, a thermoplastic mask was used to immobilize cervical spine lesions; an evacuated cushion was used for immobilization of all other spine lesions. The BrainLAB ExacTRAC® patient positioning system and a robotic couch were used to position the patient. Initial positioning was performed with two-dimensional (2D) X-ray guidance and two CBCT scans. Mid-treatment CBCT was typically performed at 10 minutes or more after the prior scan in order to identify any intra-fractional motion. Intra-translational and rotational errors were quantified based on findings from the mid-treatment CBCT images.
Results: Mid-treatment CBCT scans were performed at 1.7 ± 0.7 times per fraction. The absolute mean and standard deviations determined for intra-translations and rotations were as follows: lateral, 0.47 ± 0.45 mm (range 0-3.16 mm); longitudinal: 0.51 ± 0.73 mm (range 0-9.4 mm); vertical, 0.44 ± 0.43 mm (range 0-3.55 mm); pitch,0.27 ± 0.27° (range 0-2.20°); Roll, 0.27 ± 0.30° (range 0-2.00°); yaw, 0.23±0.24° (range 0-2.00°). Ninety-five (95)% of the fractions evaluated revealed intra-fractional motion of 1.78 mm and 1.60°.
Conclusion: 414 CBCT images taken of 114 patients undergoing SBRT demonstrated that 95% of the fractions evaluated documented intra-fractional motion of 1.78 mm and 1.60°.