Article
High-Resolution Scintillation Screen Detectors for Hadron Therapy
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Authors
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S. Ebstein
- Lexitek, Inc., Wellesley, MA, USA
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J. Wright
- Lexitek, Inc., Wellesley, MA, USA
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J. Flanz
- Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
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H. Kooy
- Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
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B. Clasie
- Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
| Published: | September 24, 2009 |
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Outline
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Background: Lexitek and its collaborators at MGH are developing high-resolution scintillation screen detectors to meet requirements for commissioning, quality assurance, and real-time monitoring of dynamically controlled scanned particle beams. Our approach is aimed at a) engineering a full-featured high-performance detector for time-integrated radiation fields (QA Detector); and b) development of a fast-tracking detector for real-time monitoring of dynamically controlled scanned beams (Fast Tracking Detector). In addition to beam measurements, we use an optical simulator with a variable spot size, 2D scanned, gated laser beam for simulating scattered and scanned beams for development.
Materials and methods: The QA Detector in Figure 1 [Fig. 1] mounts directly to a treatment nozzle for measuring beams as-delivered. Beams are incident on a scintillation screen after passing through a layer of solid water plastic sheets. The resulting scintillation is imaged by a scientific CCD. The field is 40 x 30 cm with 0.4 x 0.4 mm pixels. Detector features include a tilt sensor for recording orientation, remote control of the lens focus and aperture, and provisions for triggering and controlling exposures by external signals from the particle beam control system.
The Fast Tracking Detector has a scintillator and thin, mylar fold mirror upstream of the patient, contained in the nozzle. A fast, custom CMOS camera outside the nozzle takes sub-ms exposures of small regions of interest (ROI) surrounding the particle beam. Beam position, intensity, size and shape information are computed in real-time and the ROI tracks the moving beam.
Results: We have tested commercially available scintillators with excellent linearity and sub-microsecond time response. Figure 2 [Fig. 2] shows linearity results.
Using measurements with proton beams at MGH, we have calibrated the scintillator light output and performed simulations with dose-equivalent light levels for a 200 MeV proton beam.
Figure 3 [Fig. 3] shows a simulated 0.01 Gy treatment of a square 5x5 cm region. This measurement had fractional standard deviation of <1% averaged over the region.
The Fast Tracking Detector can successfully track spots corresponding to 0.001 Gy of dose. Figure 4 [Fig. 4] shows results for a 0.006 Gy equivalent exposure and a circular beam path.
Conclusions: We have presented promising results from scintillator based detectors. Measurements with real beams to validate the simulations are in process. A second-generation tracking camera should yield improved performance.
Acknowledgements: Support by Partners Healthcare and an SBIR grant from NIH.
