Gamma Index Calculator

The Gamma Index is a metric used in radiation therapy to assess the agreement between measured and reference dose distributions. It combines both dose difference and spatial distance into a single value, providing a comprehensive evaluation of dose delivery accuracy.

Historical Background

The Gamma Index was introduced in 1998 by Low et al. to provide a unified approach to compare two dose distributions, accounting for both dose difference and distance-to-agreement criteria. It has since become a standard tool in quality assurance for radiation therapy, particularly in advanced treatment techniques like IMRT (Intensity-Modulated Radiation Therapy).

Calculation Formula

The Gamma Index is calculated using the following formula:

\[ \text{Gamma Index} = \sqrt{\left(\frac{\text{Dose Difference}}{\text{Dose Tolerance}}\right)^2 + \left(\frac{\text{Distance to Agreement}}{\text{Spatial Tolerance}}\right)^2} \]

Example Calculation

If the measured dose is 2 Gy, the reference dose is 2.1 Gy, the distance to agreement is 3 mm, and the dose difference tolerance is 3%, the Gamma Index calculation would be:

\[ \text{Gamma Index} = \sqrt{\left(\frac{2 - 2.1}{0.03 \times 2.1}\right)^2 + \left(\frac{3}{3}\right)^2} = \sqrt{(-0.0167)^2 + 1^2} = 1.0003 \]

Importance and Usage Scenarios

The Gamma Index is critical for verifying the accuracy of dose delivery in radiotherapy. It helps ensure that the treatment plan is accurately executed, minimizing the risk of harm to patients. High gamma values indicate discrepancies that may require adjustments to the treatment plan.

Common FAQs

1. What is the Gamma Index?

   • The Gamma Index is a tool used to compare measured and reference dose distributions in radiation therapy, incorporating both dose difference and spatial agreement.

2. Why is it important?

   • It ensures the accuracy of radiation dose delivery, crucial for patient safety and effective treatment.

3. How is it interpreted?

   • A Gamma Index ≤ 1 typically indicates good agreement between the measured and reference distributions. Values > 1 suggest potential issues that need addressing.