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Dynamic Lung Tumor Tracking for Stereotactic Ablative Body Radiation Therapy
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A novel method for quantification of beam's-eye-view tumor tracking performance
Yue-Houng Hu1, Marios Myronakis1, Joerg Rottmann1
1Department of Radiation Oncology, Division of Medical Physics and Biophysics, Brigham and Women's Hospital, Dana-Farber Cancer Institute and Harvard Medical School, 75 Francis St, ASB1 L2, Boston, MA, 02115, USA.
Medical Physics
|September 10, 2017
Summary
New electronic portal imaging device (EPID) designs improve real-time tumor tracking by enhancing image quality and reducing noise. Multi-layer imager (MLI) architecture offers superior performance compared to standard single-layer imagers (SLI).
Area of Science:
- Medical Physics
- Radiotherapy Imaging
- Detector Physics
Background:
- In-treatment imaging with electronic portal imaging devices (EPIDs) is crucial for confirming patient and tumor positioning during radiotherapy.
- Current digital megavolt (MV) imagers suffer from poor image quality, hindering real-time tumor tracking performance.
- Novel EPID designs aim to enhance quantum noise response while maintaining high spatial resolution.
Purpose of the Study:
- To develop a method for quantifying improvements in tumor tracking performance.
- To identify the physical detector design characteristics that impact tumor tracking quality.
- To evaluate the effects of scintillator thickness and multi-layer imager (MLI) architecture on tracking performance.
Main Methods:
- Utilized the ideal observer signal-to-noise ratio (d') as a metric for tracking performance.
- Modeled clinically relevant detection and discrimination tasks using generalized frequency-domain imaging metrics.
- Investigated the impact of scintillator thickness and MLI architecture on modulation transfer function (MTF) and noise power spectrum (NPS).
Main Results:
- Increasing scintillator thickness in single-layer imagers (SLI) reduces noise, with significant gains up to 1000 μm.
- Multi-layer imager (MLI) architecture provides noise reduction proportional to the number of layers, with minimal impact on MTF.
- MLI detectors show superior tracking performance improvements (84-90%) compared to thick-scintillator SLIs (34-39%) for equivalent total thickness.
Conclusions:
- A novel method for quantifying tumor tracking quality was developed and applied to EPID designs.
- Improved tracking quality is primarily limited by noise power spectrum (NPS) enhancements.
- MLI architecture offers significant advantages over thick-scintillator SLIs by mitigating optical Swank noise, leading to more substantial improvements in tracking performance.
