Technical note: Feasibility of gating for dynamic trajectory radiotherapy - Mechanical accuracy and dosimetric...

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Dynamic trajectory radiotherapy (DTRT) enhances volumetric modulated arc therapy (VMAT) with simultaneous table and collimator rotations during beam delivery.
• The impact of intrafraction motion on DTRT, particularly the interplay between patient and machine motion, remains largely unexplored.

Purpose of the Study:

• To experimentally evaluate the technical feasibility of respiratory gating during DTRT delivery.
• To quantify the mechanical and dosimetric accuracy of gated DTRT.

Main Methods:

• A DTRT and VMAT plan for lung cancer was delivered to a motion phantom on a TrueBeam system.
• Respiratory gating was triggered using an external marker, and mechanical accuracy was analyzed from logfiles.
• Dosimetric accuracy was assessed using gamma evaluation (3% global/2 mm).

Main Results:

• DTRT and VMAT plans were successfully delivered with and without gating across various motion traces.
• Mechanical accuracy deviations were minimal (<0.14° for gantry, <0.08 mm for MLC).
• Gating significantly improved dosimetric performance, with gamma passing rates ≥96.7% (gated) compared to ≤88.3% (ungated).

Conclusions:

• Respiratory gating was successfully implemented during DTRT delivery on a TrueBeam system for the first time.
• Mechanical accuracy was comparable between VMAT and DTRT, with and without gating.
• Gating substantially enhanced the dosimetric accuracy of both DTRT and VMAT, indicating its clinical potential.