Visual Isocenter Position Enhanced Review (VIPER): a Cherenkov imaging-based solution for MR-linac daily QA

Area of Science:

• Medical Physics
• Radiation Oncology
• Imaging Technology

Background:

• Daily quality assurance (QA) is crucial for Magnetic Resonance Linear Accelerators (MR-Linacs).
• Verifying the coincidence of mechanical, imaging, and radiation isocenters is a key component of MR-Linac QA.
• Existing QA methods may be time-consuming or lack comprehensive 3D verification.

Purpose of the Study:

• To develop and validate a Cherenkov imaging-based system for daily QA of MR-Linacs.
• To accurately verify the mechanical-imaging-radiation isocenter coincidence.
• To provide a robust and efficient solution for clinical deployment.

Main Methods:

• A cylindrical phantom with a conical structure filled with water was designed for MR imaging.
• Cherenkov radiation was utilized to localize the radiation isocenter in 3D.
• A star shot and a four-angle sheet beam plan were delivered to the phantom.
• Custom software was developed for near-real-time data analysis.

Main Results:

• High linearity (R² > 0.99) and low RMSE (0.184 mm) were achieved for longitudinal position and optical ring diameter.
• The star shot analysis yielded a minimum circle radius of 0.34 mm.
• The total 3D isocenter coincidence was 0.83 mm, well within the 2 mm tolerance.

Conclusions:

• The Cherenkov imaging system provides an efficient, MR-safe, all-in-one solution for isocenter coincidence QA.
• This method offers a direct measurement of 3D isocentricity.
• The system is clinically deployable and enhances MR-Linac safety and accuracy.