A Varian DynaLog file-based procedure for patient dose-volume histogram-based IMRT QA

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Quality Assurance

Background:

• Intensity-Modulated Radiation Therapy (IMRT) requires precise quality assurance (QA) to ensure accurate dose delivery.
• Verifying patient-specific IMRT plans is crucial for treatment efficacy and safety.
• Existing QA methods may have limitations in accurately assessing patient-specific dose delivery.

Purpose of the Study:

• To develop and validate a novel method for patient-specific IMRT QA using dynamic log files (DynaLog).
• To assess the accuracy of dose reconstruction from DynaLog data.
• To evaluate the clinical applicability of the DynaLog-based QA method across various treatment sites.

Main Methods:

• Analysis of Varian linear accelerator dynamic MLC log files (DynaLog) using MATLAB.
• Dose reconstruction of actual patient treatment plans using the Eclipse treatment planning system.
• In-phantom ionization chamber and Electronic Portal Imaging Device (EPID) measurements for validation.
• Introduction of intentional errors to assess method sensitivity.
• Application to clinical plans for prostate, lung, breast, and head and neck cancers.

Main Results:

• A significant positive correlation (R² = 0.9993) was found between measured dose variations and DynaLog-based reconstructed dose changes.
• DynaLog-based fluence reconstruction accuracy was comparable to established portal dosimetry resolution (3%/3 mm).
• Dose-volume histogram (DVH) metrics effectively evaluated the impact of delivery errors on patient dose.

Conclusions:

• The DynaLog-based dose reconstruction method is a suitable tool for patient-specific IMRT QA.
• This patient DVH-based IMRT QA approach enhances treatment verification accuracy.
• The method provides a reliable means to assess dose delivery errors in clinical IMRT practice.