Scintillation imaging as a high-resolution, remote, versatile 2D detection system for MR-linac quality assurance

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Quality Assurance

Background:

• Routine quality assurance (QA) is critical for magnetic resonance guided radiotherapy (MRgRT).
• Traditional QA methods can be time-consuming and may not be fully compatible with MR environments.
• Developing efficient, MR-compatible QA tools is essential for safe and effective MRgRT.

Purpose of the Study:

• To evaluate the potential benefits of remote camera-based scintillation imaging for MRgRT linear accelerator QA.
• To demonstrate the system's capability for various routine QA measurements.
• To assess its suitability as a versatile and MR-compatible QA solution.

Main Methods:

• A CMOS camera with an intensifier imaged a scintillation screen exposed to a 6 MV FFF x-ray beam from a 0.35 T MR-linac.
• Projective transform corrected for oblique viewing angles.
• Output sensitivity, constancy, field profiles, multileaf collimator (MLC) shifts, picket fence tests, and star-shots were measured and benchmarked against ion chambers and film.

Main Results:

• The scintillation imaging system demonstrated comparable sensitivity and linearity to ion chambers for output changes down to 0.5 MU (R² = 0.99).
• High-resolution profiles showed agreement with field sizes (<2 mm FWHM for fields <15 cm).
• MLC shifts as small as 0.5 mm were detected with <0.1 mm accuracy, and MLC positions were within ±1 mm tolerance.

Conclusions:

• Remote scintillation imaging provides a rapid, versatile, and MR-compatible solution for routine MRgRT QA.
• The method offers high-resolution, instantaneous data acquisition without post-irradiation readout.
• Full automation could establish this as a simple, effective, and adaptable QA tool for all medical accelerators.