3D DVH-based metric analysis versus per-beam planar analysis in IMRT pretreatment verification

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Quality Assurance

Background:

• Pretreatment analysis of intensity-modulated radiation therapy (IMRT) plans is crucial for ensuring treatment accuracy and patient safety.
• Traditional gamma analysis methods have limitations in reflecting the clinical relevance of detected dose discrepancies.
• Developing robust methods for verifying IMRT delivery is essential for modern radiation oncology.

Purpose of the Study:

• To evaluate the clinical relevance and accuracy of different pretreatment IMRT analysis methods.
• To compare the efficacy of gamma analysis versus dose-volume histogram (DVH) metrics using real-world measurements.
• To assess the reliability of 3DVH software for correlating planar dose discrepancies with clinical outcomes.

Main Methods:

• Performed in-phantom tests to assess the sensitivity of various analysis techniques to introduced errors.
• Measured beam fluences using a commercial 2D detector array (MapCHECK 2).
• Compared per-beam planar analysis, 3D gamma analysis, and DVH evaluation using 3DVH software for 17 patient plans.

Main Results:

• Per-beam gamma analysis exhibited false positives and false negatives, with a 3%/3 mm criterion being too lenient.
• 3DVH software accurately described DVH for plans with introduced errors, showing agreement within 2% dose or volume.
• DVH analysis revealed systematic undercoverage of target dose (D98, D95) compared to treatment planning system predictions.

Conclusions:

• No correlation was found between the gamma index and the clinical impact of dose discrepancies across various evaluation methods.
• DVH analysis proved more reliable than gamma index analysis in accounting for discrepancies and their clinical relevance.
• 3DVH software is a reliable tool for correlating measured dose discrepancies with clinical tolerance for target and organs at risk.