Compact bunker shielding assessment for 1.5 T MR-Linac

Area of Science:

• Medical Physics
• Radiation Oncology
• Magnetic Resonance Imaging

Background:

• Magnetic resonance-guided linear accelerators (MR-Linacs) integrate MRI with radiotherapy.
• Evaluating radiation leakage from MR-Linacs is crucial for patient and staff safety.
• Bunker shielding design must account for both primary and secondary radiation in MR-Linac systems.

Purpose of the Study:

• To assess the impact of the 1.5 Tesla (T) magnetic field from an MR-Linac on radiation leakage doses.
• To verify the effectiveness of specialized bunker shielding in reducing radiation exposure.
• To ensure compliance with international radiation safety standards for MR-Linac facilities.

Main Methods:

• Radiation leakage doses were measured in a minimum-sized bunker housing a 1.5 T MR-Linac Unity system.
• Shielding effectiveness was evaluated by comparing dose measurements before and after magnetic field application.
• Intrinsic vibration and magnetic field strength were inspected at the treatment isocenter.

Main Results:

• The specialized shielding design achieved a five-fold reduction in radiation leakage dose.
• Measured leakage doses ranged from 0.05 to 12.2 µSv/week, complying with international limits.
• While a slight increase in leakage dose was observed with the magnetic field, it was within experimental uncertainty, precluding definitive conclusions.

Conclusions:

• The evaluated MR-Linac system, with specialized shielding, meets stringent radiation safety requirements.
• The 1.5 T magnetic field's effect on radiation leakage dose could not be definitively determined due to experimental uncertainty.
• MR-Linac technology can be implemented safely within standard bunker designs with appropriate shielding measures.