Integrated megavoltage portal imaging with a 1.5 T MRI linac

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Diagnostic Imaging

Background:

• Hybrid 1.5 T MRI linac (MRL) systems combine magnetic resonance imaging (MRI) with linear accelerators (linacs) for advanced cancer treatment.
• Accurate patient positioning is critical for effective radiotherapy, requiring robust verification tools.

Purpose of the Study:

• To investigate the feasibility and performance of integrating a megavoltage (MV) portal imager with a 1.5 T MRL system.
• To assess the potential of MV imaging for position verification and system calibration in an MRI-guided radiotherapy setting.

Main Methods:

• A standard aSi MV detector panel was added to the existing 1.5 T MRL system.
• Qualitative and quantitative performance assessments were conducted for the integrated system.
• Simultaneous MR imaging and MV transmission imaging were performed to evaluate mutual interference and image quality.

Main Results:

• Simultaneous MR and MV imaging were achieved without interference.
• MV image quality was affected by beam transmission and isocenter distance, but bony anatomy and field edges were detectable at 0.4 cGy.
• The integrated MV portal imager demonstrated utility for position verification, field edge checks, and coordinate system calibration.

Conclusions:

• Integrating an MV portal imager with an MRL is feasible and enhances system capabilities.
• The MV imager serves as an independent tool for MRI-guided radiotherapy, aiding in patient positioning and protocol benchmarking.