Author: Yi An, David J. Carlson, Zhe (Jay) Chen, Jun Deng, Dae Yup Han, Sameer Taneja 👨🔬
Affiliation: Yale School of Medicine, Yale University School of Medicine, Department of Therapeutic Radiology, Yale University School of Medicine 🌍
Purpose: Spine Stereotactic radiosurgery (SSR) delivers a large radiation dose and utilizes narrow PTV margins, on the order of 1 mm, to avoid excess dose to the spinal cord. Because of this, intrafraction tumor tracking is important to limit excess doses outside of the PTV. Previous works have looked at using triggered imaging but noted limitations with 2D imaging. This work combines multiple CBCTs along with triggered imaging during spine SBRT beam delivery to characterize intrafraction motion.
Methods: Spine Stereotactic radiosurgery (SSR) delivers a large radiation dose and utilizes narrow PTV margins, on the order of 1 mm, to avoid excess dose to the spinal cord. Because of this, intrafraction tumor tracking is important to limit excess doses outside of the PTV. Previous works have looked at using triggered imaging but noted limitations with 2D imaging. This work combines multiple CBCTs along with triggered imaging during spine SBRT beam delivery to characterize intrafraction motion.
Results: The average patient shift magnitudes [cm or degrees] determined by CBCT, in the vertical, longitudinal, lateral, rotation, pitch, and roll directions, respectively, were (0.30mm, 0.47mm. 0.39mm, 1.36°, 1.00°, and 0.80°) for the initial setup, (0.02, 0.02, 0.05, 0.13, 0.16, and 0.07) for the verification scan, and (0.02, 0.02, 0.04, 0.14, 0.11, and 0.15) for the between arcs scan. No treatment delivery was stopped during an arc due to triggered imaging utilized to monitor the patient's motion.
Conclusion: After the initial setup CBCT, there was sub-millimeter and sub-degree patient movement on both the verification and the between arc scans. Triggered imaging correctly identified sub-1mm movement on 88% of fractions.