Technical Note: Motion-perturbation method applied to dosimetry of dynamic MLC target tracking--A proof-of-concept

Area of Science:

• Medical Physics
• Radiotherapy
• Radiation Oncology

Background:

• Virtual Motion Simulation (VMS) enables dose estimation for moving targets.
• Extending VMS to dynamic multileaf collimator (MLC)-tracking treatments is a novel application.
• Accurate dose reconstruction is critical for advanced radiotherapy techniques.

Purpose of the Study:

• To introduce a modified VMS method for dose estimation in dynamic MLC-tracking treatments.
• To quantify the performance of this modified VMS method as a proof-of-concept.
• To evaluate the applicability of VMS for real-time tracking in radiotherapy.

Main Methods:

• Direct measurements using a moving biplanar diode array for VMS dose estimate verification.
• Simulation of a tracking environment with dynamic MLC apertures and accelerator table movement.
• Assessment of VMS sensitivity to simulated tracking latency (0-700 ms) and temporal dose gradients.

Main Results:

• Agreement rates (2% global/2 mm gamma) between VMS and biplanar dosimeter exceeded 96% when physical and virtual latencies matched.
• Close tracking agreement was observed up to 200 ms (10% cutoff) and 300 ms (50% cutoff) of induced latency.
• The error in cumulative dose due to 200 ms VMS time resolution was estimated to be less than 0.5% in modulated beams.

Conclusions:

• The modified VMS approach is a viable method for dose estimation in MLC-tracking radiotherapy.
• The VMS method's accuracy is suitable for tracking applications with leaf speeds comparable to current Varian accelerators.
• This technique holds promise for improving dose accuracy in complex, dynamic radiation treatments.