2D IMRT QA passing rate dependency on coronal plane.

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Quality Assurance

Background:

• Intensity modulated radiation therapy (IMRT) requires rigorous quality assurance (QA) to ensure accurate dose delivery.
• Complex beam angles and multileaf collimator (MLC) arrangements in IMRT necessitate validation before patient treatment.

Purpose of the Study:

• To investigate the relationship between dose gradient and the passing rate of IMRT QA measurements.
• To determine if dose gradient can predict QA outcomes across different measurement planes.

Main Methods:

• Forty IMRT plans were delivered and measured using a 2D ion chamber array.
• Eleven plans were additionally measured at multiple coronal planes.
• Dose gradient metrics and QA passing rates (3%/3 mm and 3%/2 mm criteria) were analyzed.

Main Results:

• A general correlation was observed between dose gradient and QA passing rates, with an average distance correlation of 0.54 ± 0.04 for the lateral dose gradient.
• QA passing rates varied with the coronal slice, but the correlation with dose gradient was not consistently predictable.
• Hypothesized negative correlations between dose gradient and passing rate were not always observed.

Conclusions:

• While dose gradient influences IMRT QA passing rates, its predictive power is limited.
• The choice of coronal plane for QA significantly affects passing rates.
• Dose gradient alone is insufficient to reliably predict optimal QA measurement slices.