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Updated: Apr 15, 2026
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Dynamic Lung Tumor Tracking for Stereotactic Ablative Body Radiation Therapy
Published on: June 7, 2015
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The first experimental implementation of real-time dose-guided MLC tracking using an MRI-linac
Emily A Hewson1, Pim T S Borman2, Bas W Raaymakers2
1Image X Institute, Faculty of Medicine and Health, University of Sydney, Australia.
Summary
This study demonstrates real-time dose-guided adaptive radiation therapy (ART) using MLC tracking for improved accuracy. The novel dose-guided ART system achieved dosimetric accuracy comparable to geometry-guided tracking, addressing intrafraction motion errors.
Area of Science:
- Medical Physics
- Radiation Oncology
- Image-Guided Therapy
Background:
- Intrafraction motion during radiation therapy can lead to significant dose errors.
- Current geometry-based tracking methods do not fully correct for these motion-induced errors.
- Real-time dose-guided adaptive radiation therapy (ART) offers a potential solution but requires experimental validation.
Purpose of the Study:
- To report the first experimental implementation of real-time dose-guided MLC tracking.
- To evaluate the performance of dose-guided MLC tracking in addressing intrafraction motion.
- To compare dose-guided tracking with geometry-guided tracking and no tracking.
Main Methods:
- Integration of dose-guided MLC tracking with an MRI-linac system.
- Utilizing MRI guidance for motion phantom monitoring.
- Adapting treatment by accumulating delivered doses and optimizing MLC positions to minimize dose errors.
- Measuring tracking performance using film and plastic scintillation dosimeters (PSD) in single and multi-target scenarios.
- Assessing end-to-end latency of the tracking system.
Main Results:
- For single targets, dose-guided tracking achieved 90.2% gamma-pass rates (2%/2mm), comparable to geometry-guided tracking (91.8%), significantly outperforming no tracking (42.6%).
- Mean PSD dose differences were 2.4% for dose-guided tracking versus 2.0% for geometry-guided tracking, compared to 26.8% for no tracking.
- In multi-target setups, dose-guided tracking yielded 86.7% gamma-pass rates, outperforming geometry-guided tracking (77.0%) and no tracking (44.5%).
- The end-to-end latency for dose-guided MLC tracking was measured at 545 ± 16 ms.
Conclusions:
- Real-time dose-guided ART was successfully implemented experimentally for the first time.
- The dosimetric accuracy of dose-guided tracking was found to be comparable to geometry-guided tracking.
- Identified limitations provide a roadmap for future improvements to fully realize the clinical benefits of dose-guided ART.
