Using an EPID for patient-specific VMAT quality assurance.

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Quality Assurance

Background:

• Volumetric Modulated Arc Therapy (VMAT) delivers precise radiation doses.
• Accurate positioning of multileaf collimator (MLC) apertures is crucial for VMAT plan integrity.
• Patient-specific quality assurance (QA) is essential for verifying treatment delivery accuracy.

Purpose of the Study:

• To develop and validate a patient-specific QA method for verifying MLC apertures in VMAT plans.
• To utilize electronic portal imaging device (EPID) cine images for automated QA.
• To assess the accuracy and efficiency of the developed QA method.

Main Methods:

• VMAT plans were generated using a treatment planning system (TPS).
• Pretreatment QA was performed using DICOM images from a Varian EPID in continuous acquisition mode.
• In-house software was developed to interpolate EPID images and compare them against TPS MLC data, analyzing leaf position mismatches.

Main Results:

• The developed QA method was applied to seven patient VMAT plans.
• Analysis revealed that the highest rates of MLC leaf mismatches were dependent on the specific treatment plan.
• The method successfully identified discrepancies in MLC leaf positions.

Conclusions:

• The developed in-house software provides an automated solution for verifying MLC leaf positions in VMAT plans.
• This EPID-based QA method enhances the accuracy of VMAT delivery by confirming control point accuracy.
• The approach is effective for patient-specific QA in VMAT radiotherapy.