Intrafractional motion detection for spine SBRT via X-ray imaging using ExacTrac Dynamic

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Technology

Background:

• Spine stereotactic body radiotherapy (SBRT) requires high safety standards due to proximity to the spinal cord.
• Individualized immobilization devices (e.g., vacuum cushions) are typically used to minimize motion during spine SBRT.
• Accurate intrafraction motion monitoring is essential for safe and effective treatment delivery.

Purpose of the Study:

• To evaluate intrafractional motion during spine SBRT.
• To assess the efficacy of patient monitoring using orthogonal X-ray imaging without individualized immobilization.
• To determine if intrafraction motion management can maintain safety standards in spine SBRT.

Main Methods:

• Collected intrafractional X-ray data from 29 patients undergoing 79 fractions of spine SBRT.
• Utilized the ExacTrac Dynamic (ETD) System for high-accuracy patient monitoring in six degrees of freedom (6 DOF).
• Implemented repositioning protocols for translational deviations >0.7 mm and rotational deviations >0.5°.

Main Results:

• 15% of image pairs (138/925) showed deviations exceeding tolerance levels.
• A total of 191 out-of-tolerance deviations were recorded across all 6 DOF.
• Maximum translational deviations reached 2.8 mm, and maximum rotational deviations reached 2.6°.

Conclusions:

• Intrafraction motion detection and patient repositioning using X-ray imaging (ETD System) enhance safety in spine SBRT.
• The use of intrafractional imaging with strict repositioning thresholds may allow for the omission of individualized immobilization devices.
• This approach can improve the safety of delivering high biologically effective doses (BED) in critical spinal locations.