Quantifying radiotherapy beam quality: an analysis using gamma passing rates

Area of Science:

• Medical Physics
• Radiation Oncology
• Accelerator Physics

Background:

• Percentage Depth Dose (PDD) and profile curves are essential for evaluating accelerator beam quality and energy stability.
• Traditional methods for machine Quality Assurance (QA) may not capture subtle variations in dose outputs.

Purpose of the Study:

• To evaluate the effectiveness of Gradient Power Ratio (GPR) analysis for machine QA.
• To compare GPR analysis with traditional methods for assessing accelerator dose outputs.

Main Methods:

• GPRs were used to analyze 1D and 2D Profile metrics and PDD data against commissioning data from water tank ASCII files.
• A 10% lower percentage dose cutoff was applied for GPR calculations.
• A 1%/1 mm criterion was adopted for both 1D and 2D GPR analyses, with comparisons made to traditional QA checks.

Main Results:

• GPR analysis demonstrated superior capability in comprehensive data analysis over traditional methods.
• 1D curve passing rates (γ ≤ 1) were 96.19%, 100%, and 93.46%.
• The 2D PDD image passing rate was 99.57%, revealing significant dose differences at the open field corners.

Conclusions:

• GPRs are more sensitive to subtle data changes than traditional methods, offering valuable insights into accelerator beam status.
• GPR analysis enhances the precision of machine QA in radiation therapy.