Evaluation of linear accelerator gating with real-time electromagnetic tracking.

Area of Science:

• Medical Physics
• Radiation Oncology
• Biomedical Engineering

Background:

• Intrafraction organ motion during radiotherapy can lead to significant dosimetric errors.
• External sensors for gating often lack correlation with internal tumor position.
• Real-time internal tumor location monitoring is crucial for accurate radiation delivery.

Purpose of the Study:

• To evaluate a novel beam gating technique using implanted wireless transponders for real-time tumor tracking.
• To assess the dosimetric benefits and system latencies of internal position monitoring for radiotherapy.
• To determine if wireless transponders can improve accuracy without additional imaging dose.

Main Methods:

• Developed an interface between an electromagnetic tracking system (Calypso) and a linear accelerator (Varian Trilogy).
• Utilized a film phantom on a motion platform simulating lung motion.
• Performed beam gating based on real-time signals from wireless transponders.

Main Results:

• Beam gating with internal monitoring significantly improved dose gradients (up to twofold increase).
• Gating reduced the percentage of points with dose errors (3.4% vs. 32.1% without gating).
• Observed system latencies (75.0 ms beam on, 65.1 ms beam off) suitable for gating.

Conclusions:

• A novel method for linear accelerator gating using internal wireless fiducial markers was successfully implemented.
• This technique provides accurate tumor tracking without ionizing radiation for imaging.
• The observed latencies and dosimetric improvements demonstrate the efficacy of this approach for motion management in radiotherapy.