Technical Note: The first live treatment on a 1.0 Tesla inline MRI-linac

Area of Science:

• Medical Physics
• Oncology
• Radiotherapy

Background:

• Advancements in radiotherapy require precise imaging for accurate tumor targeting.
• Magnetic Resonance Imaging (MRI)-Linear Accelerator (Linac) systems offer integrated imaging and treatment capabilities.
• Adapting human-scale MRI-Linac systems for preclinical animal studies is crucial for developing novel cancer therapies.

Purpose of the Study:

• To report the first live imaging and radiation delivery using a prototype 1.0 T inline MRI-Linac system in a rat brain tumor model.
• To evaluate the feasibility of using real-time MRI guidance for tumor localization and dose delivery in an animal study.
• To assess the system's capability for monitoring animal motion during irradiation.

Main Methods:

• A 1.0 T MRI-Linac was adapted for animal studies using a custom radiofrequency (RF) coil.
• A Fischer rat with a 9L glioma tumor was anesthetized and positioned in the MRI-Linac.
• MRI was used for tumor localization after contrast agent administration, followed by a 10 Gy whole-brain radiation dose delivery.
• Real-time imaging was employed throughout irradiation to monitor the animal and target position.

Main Results:

• The MRI-Linac system achieved a signal-to-noise ratio (SNR) of 38 in the rat brain.
• Postcontrast imaging successfully identified a 5 mm brain tumor.
• Real-time 2 Hz imaging effectively monitored respiration and intrafractional motion without impacting SNR.
• In vivo film dosimetry confirmed accurate dose delivery, with a total procedure time of 35 minutes.

Conclusions:

• The study successfully demonstrated MRI-guided localization and whole-brain radiation delivery in a rat brain tumor model.
• Real-time imaging during irradiation proved adequate for monitoring breathing and enabling exception gating.
• This work marks the first live application of a high-field inline MRI-Linac system in a preclinical setting.