A new methodology for inter- and intrafraction plan adaptation for the MR-linac

Area of Science:

• Medical Physics
• Radiation Oncology
• Medical Imaging

Background:

• Hybrid MRI and linear accelerator (MR-linac) machines offer real-time patient anatomy visualization during radiation delivery.
• Adapting radiation plans to dynamic anatomical changes is crucial for maximizing treatment efficacy and minimizing toxicity.
• Current treatment planning systems often lack the capability for online adaptation to intra- and interfraction anatomical variations.

Purpose of the Study:

• To present a novel intensity-modulated radiotherapy (IMRT) treatment planning algorithm capable of compensating for patient anatomy changes.
• To enable online plan adaptation to real-time anatomical data provided by hybrid MR-linac systems.
• To demonstrate the algorithm's effectiveness in achieving ideal dose distribution without final segment weight optimization (SWO).

Main Methods:

• Development of an iterative sequencing loop for online anatomy updates.
• Implementation of an inter- and intrafraction adaptation scheme for treatment plan adjustments.
• Validation using artificial baseline shifts in three kidney cancer cases with varying target volumes.

Main Results:

• The proposed algorithm successfully accounts for intrafraction motion, delivering precise dose to targets while minimizing exposure to organs at risk (OARs) compared to conventional plans.
• The interfraction adaptation scheme allows for effective dose delivery by adjusting to anatomical changes during multi-fraction treatments.
• The system achieves convergence to the ideal dose distribution without requiring a final segment weight optimization (SWO).

Conclusions:

• The developed IMRT treatment planning algorithm effectively adapts to patient anatomy changes in an online regime, leveraging data from hybrid MR-linac machines.
• This approach enhances dose accuracy and OAR sparing, offering a significant improvement over conventional treatment planning.
• The algorithm facilitates adaptive radiotherapy, enabling robust treatment delivery even with significant interfraction anatomical variations.