A method for determining the gantry angle for megavoltage cone beam imaging

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Image Analysis

Background:

• Accurate gantry angle is critical for quality assurance in megavoltage cone beam imaging (MVCBI).
• Existing methods for gantry angle determination may have limitations in dynamic arc mode during image acquisition.
• Real-time, precise gantry angle information is essential for safe and effective radiation delivery.

Purpose of the Study:

• To develop and validate a novel method for determining the gantry angle during MVCBI using multileaf collimator (MLC) leaf positions.
• To assess the accuracy of the proposed method in dynamic arc mode where the gantry moves continuously.
• To establish the suitability of this technique for clinical application in MVCBI.

Main Methods:

• A new algorithm was developed to detect multileaf collimator (MLC) leaf positions directly from projection images acquired during MVCBI.
• The algorithm compares detected MLC leaf positions against a stationary reference leaf to infer gantry angle.
• The accuracy of the developed algorithm was validated by comparing its results against gantry angles determined using fiducial markers.

Main Results:

• The proposed method successfully detects MLC leaf positions in projection images acquired during dynamic arc mode.
• The algorithm demonstrated high accuracy, with a root-mean-square (rms) error of 0.26 degrees when compared to fiducial marker-based angle determination.
• The achieved accuracy is sufficient for the demanding requirements of MVCBI.

Conclusions:

• The developed MLC-based method provides an accurate and reliable means of determining gantry angle during MVCBI.
• This technique is particularly valuable for dynamic arc therapy where continuous gantry motion occurs.
• The findings suggest this method can enhance quality assurance and potentially improve treatment accuracy in radiation oncology.