Dose verification for respiratory-gated volumetric modulated arc therapy

Area of Science:

• Radiation Oncology
• Medical Physics
• Image-Guided Therapy

Background:

• Treating moving tumors with radiation therapy presents challenges due to respiratory motion.
• Volumetric Modulated Arc Therapy (VMAT) offers precise dose delivery, and respiratory gating enhances accuracy for moving targets.

Purpose of the Study:

• To adapt and validate a dose reconstruction technique for evaluating the accuracy of respiratory-gated VMAT delivery.
• To assess the fidelity of VMAT treatment on a Varian TrueBeam system under simulated patient breathing conditions.

Main Methods:

• A log-file-based dose reconstruction technique was adapted and combined with ion chamber array measurements (Seven29).
• VMAT plans for lung and pancreas tumors were delivered to a phantom with and without gating across various respiratory periods.
• The adapted technique and measurements were used to evaluate dose delivery accuracy and fidelity.

Main Results:

• Comparison of gated and non-gated VMAT delivery showed good agreement, with gamma-index passing rates above 99% (1%/1 mm criteria).
• Dose reconstruction and measurements confirmed the TrueBeam system's ability to accurately deliver gated VMAT plans.
• The system demonstrated sensitivity to introduced delivery errors, with significant dosimetric differences detected.

Conclusions:

• A validated dose reconstruction procedure is effective for assessing respiratory-gated VMAT accuracy.
• The Varian TrueBeam system accurately delivers respiratory-gated VMAT treatments under clinical conditions.
• This methodology provides a valuable tool for quality assurance in advanced radiation therapy.