Technical Note: Performance of CyberKnife^® tracking using low-dose CT and kV imaging

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Image-Guided Interventions

Background:

• Accurate tumor targeting is essential for effective radiotherapy.
• CyberKnife is a robotic radiosurgery system that relies on precise tracking.
• CT imaging protocols and X-ray techniques can influence tracking accuracy.

Purpose of the Study:

• To evaluate the impact of CT imaging parameters on CyberKnife tracking accuracy.
• To assess the influence of in-room X-ray techniques on tracking performance.
• To determine the optimal settings for CyberKnife tracking accuracy using end-to-end tests.

Main Methods:

• End-to-end tests were conducted using head and thorax phantoms with CyberKnife tracking methods (6D skull, fiducial, spine, lung).
• Phantoms were scanned using low-dose and high-dose CT protocols to generate corresponding digitally reconstructed radiographs (DRRs).
• Initial alignment (Δ(Align)) and total targeting accuracy (E2E) were measured, along with variations in in-room X-ray techniques.

Main Results:

• All tracking methods achieved end-to-end accuracy within 0.95 mm, even with low-dose CT protocols.
• The difference in alignment and accuracy between low- and high-dose CT protocols was minimal (<0.32 mm).
• In-room X-ray techniques resulting in high noise or saturation led to alignment accuracy exceeding 1 mm.

Conclusions:

• Low-dose CT protocols are sufficient for CyberKnife tracking accuracy, provided target delineation is adequate.
• Optimal CT protocol selection should prioritize target contouring needs.
• High tracking accuracy is achievable with in-room X-ray imaging techniques that yield high-quality images.