Poster - Thurs Eve-33: Initial implementation of a novel, measurement-based IMRT QA method

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Quality Assurance

Background:

• Current measurement-based quality assurance (QA) for intensity-modulated radiation therapy (IMRT) uses composite dose delivery to phantoms, limiting direct dosimetric evaluation against patient anatomy.
• This traditional method does not allow for a precise assessment of the delivered treatment in relation to the patient's specific anatomical structures.

Purpose of the Study:

• To implement and evaluate a novel measurement-based IMRT QA method for accurate 3D dose distribution reconstruction within a patient model.
• To enable direct dosimetric comparison of delivered treatment to patient anatomy, enhancing treatment verification accuracy.

Main Methods:

• Developed a novel measurement-based IMRT QA method using a 2D array of dose chambers (MatriXX) on a linear accelerator to capture delivered fluence.
• Integrated measurement data with treatment planning system (TPS) data using COMPASS software, which includes a dose calculation engine and beam modeling.
• Validated the method using the RPC Head&Neck phantom and two clinical prostate cases, comparing reconstructed doses and DVHs against TPS calculations.

Main Results:

• The beam model in COMPASS software demonstrated high accuracy, predicting percentage depth dose within 1.5% and profiles within 2.0% (in-field) and 2.5% (out-of-field).
• Reconstructed doses in test plans were largely within 2% of TPS calculations, with DVHs comparing within 1.2%.
• Reconstructed doses were successfully overlaid on CT data and contoured structures, facilitating clinical understanding of discrepancies.

Conclusions:

• The novel measurement-based IMRT QA method provides accurate 3D dose reconstruction, enabling direct dosimetric evaluation against patient anatomy.
• This method enhances the clinical utility of IMRT QA by allowing for a more precise and anatomically relevant assessment of treatment delivery.
• The findings suggest this approach significantly improves the verification process for IMRT treatments.