Patient-specific quality assurance method for VMAT treatment delivery

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Volumetric Modulated Arc Therapy (VMAT) enables precise radiotherapy delivery through optimized dose rate, gantry speed, and dynamic multileaf collimator (DMLC) leaf positions.
• Accurate dose reconstruction is crucial for verifying treatment delivery and enabling adaptive radiotherapy strategies.

Purpose of the Study:

• To develop and validate a practical method for patient-specific volumetric dose reconstruction of VMAT treatments using DMLC and treatment controller log (Dynalog) files.
• To assess the accuracy of VMAT delivery by comparing reconstructed doses with planned doses.

Main Methods:

• A custom software system converted Dynalog file data (gantry angle, dose rate, leaf positions) into DICOM-compliant VMAT plans.
• Reconstructed dose distributions were computed in the treatment planning system and compared with original plans using standard evaluation tools.
• Dosimetric accuracy was validated using the MATRIXX system in a phantom, with gamma index analysis.

Main Results:

• Log files directly enabled accurate dose reconstruction without phantom measurements.
• Leaf position errors averaged 0.15 mm (max -0.26 mm), gantry angle deviation was <1°, and total monitor units (MU) were within 0.5 of planned values.
• Differences between reconstructed and intended dose matrices were <1.46%, with >96% agreement in phantom measurements.

Conclusions:

• Automated analysis of Dynalog files provides a reliable method for volumetric dose reconstruction in VMAT.
• This methodology offers a valuable, efficient platform for quality assurance and future adaptive radiotherapy without additional measurements.