Technical Note: Cumulative dose modeling for organ motion management in MRI-guided radiation therapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Medical Imaging

Background:

• MRI-guided radiation therapy (MRgRT) enables real-time visualization during treatment.
• Accurate dose accumulation is crucial for effective radiation therapy, especially with moving organs.

Purpose of the Study:

• To develop a method for continuous online dose accumulation in MRgRT.
• To assess the impact of internal organ motion on cumulative dose using this method.

Main Methods:

• Intensity-modulated radiation therapy (IMRT) plans were analyzed by partitioning into unique apertures.
• Monte Carlo simulations calculated dose for each aperture on 4D-CT phases.
• Deformable image registration mapped cine-MRI frames to 4D-CT phases, enabling dose warping and accumulation.

Main Results:

• The method was applied to a liver cancer MRgRT case.
• Cumulative dose variations of up to 5% (minimum dose) and 7% ($$) were observed due to organ motion.
• Differences were noted between free-breathing and respiration-gated delivery compared to static anatomy.

Conclusions:

• A novel technique for continuous online dose accumulation during MRgRT was successfully demonstrated.
• Pre-calculation of dose per aperture and phase, combined with a mapping scheme, reduces computational load.
• This approach is suitable for evaluating organ motion effects in real-time MRgRT applications.