Enhancing Delivery Efficiency on the Magnetic Resonance-Linac: A Comprehensive Evaluation of Prostate Stereotactic...

Area of Science:

• Radiation Oncology
• Medical Physics
• Image-Guided Therapy

Background:

• Long treatment sessions are a significant limitation in MRI-guided adaptive radiation therapy (MRIgART).
• Improving delivery efficiency is crucial for expanding the clinical utility of MRIgART systems, such as the MR-linac.

Purpose of the Study:

• To enhance MR-linac delivery efficiency using dedicated Volumetric Modulated Arc Therapy (VMAT) optimization and delivery techniques.
• To compare VMAT plan and delivery quality against step-and-shoot intensity-modulated radiation therapy (IMRT) for prostate stereotactic body radiation therapy within MRIgART.

Main Methods:

• Retrospective replanning of 10 prostate cancer patients using step-and-shoot IMRT and two VMAT techniques (clinical Hyperion and research OFL+PGD) on a 1.5T MR-linac.
• Evaluation of adapt-to-position workflows ('optimize weights' and 'optimize shapes') for both IMRT and VMAT.
• Assessment of treatment efficiency (optimization, delivery, total time) and plan quality (organ at risk sparing, gamma analysis).

Main Results:

• VMAT techniques (Hyp-VMAT and OFL+PGD-VMAT) significantly reduced total treatment time compared to clinical Hyp-IMRT.
• Adapt-to-position with VMAT-Weights showed substantial time reduction versus IMRT-Shapes.
• All VMAT plans achieved high gamma passing rates (>96%), with superior delivery efficiency (89.7%) compared to IMRT (50.0%).

Conclusions:

• Integrating VMAT into MRIgART substantially decreases treatment session duration.
• VMAT achieves this efficiency gain while preserving equivalent plan quality compared to traditional IMRT methods.