Intrafractional Target Motion during Spinal Stereotactic Body Radiation Therapy (SBRT)

Details

18:15 - 20:15 | Mon 5 Mar | Caribbean ABC | MoPO.77

Session: Poster Session # 1 and BSN Innovative Health Technology Demonstrations

Abstract

Radiotherapy (RT) patients with spinal metastases may receive large tumoricidal doses to targets in close proximity to the spinal cord. Any patient-motion may result in the spinal cord receiving doses above the predetermined tolerance, potentially resulting in spinal myelopathy. We retrospectively investigated the frequency and magnitudes of spinal target-motion of patients, and thereby evaluate the efficacy of the patient immobilization system. Using a cohort of 325 spine patients receiving SBRT, 589 spinal sites were analyzed. X-ray images taken during RT were used to detect intra-fractional motion of the vertebral targets. All corrections to patient position were recorded. Only 2% of all treatments required intervention due to patient motion. Twelve spinal sites had at least one translational or rotational shift during RT. All translational shifts were < 4 mm, though there was one outlier at 6.1 mm. For the rotational motion, the pitch and roll shifts occurred within 1.1°, half of them were > 0.5°; and the yaw had the largest shifts with an average of 1.5°. Combining the three types of shifts into one vector, the average of the translational shift vector was 3 mm while the average of the rotational shift vector was 2°. Treatment immobilization of the patient's body is effective in keeping the target vertebra correctly positioned during RT. The use of intra-fractional imaging made it possible to detect/correct changes in target position in a small number of outlier patient.