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BEST IN PHYSICS (IMAGING) - Superficial Dose Imaging Based On Cherenkov Radiation Emission During Megavoltage External Beam Radiotherapy

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R Zhang

R Zhang1*, C Fox2, L Jarvis3, A Glaser4, D Gladstone5, B Pogue6, (1) Dartmouth College, Hanover, NH, (2) Dartmouth-Hitchcock Medical Center, Hanover, NEW HAMPSHIRE, (3) Dartmouth-Hitchcock Medical Center, Hanover, NEW HAMPSHIRE, (4) Dartmouth College, Hanover, NH, (5) Dartmouth-Hitchcock Med. Ctr., Lebanon, NH, (6) Dartmouth College, Hanover, NH

TH-A-141-9 Thursday 8:00AM - 9:55AM Room: 141

Purpose:
To show that Cherenkov emission generated by megavoltage X-ray beams could be imaged in real time during external beam radiotherapy. Images of Cherenkov emission could be applied for quality assurance (QA) and estimate the superficial dose distribution for complex surface profiles.

Methods:
Cherenkov radiation has been documented to be generated by MeV external beam radiotherapy in both water and tissue. A typical breast cancer treatment plan was adopted to irradiate the breast and torso region of an anthropometric phantom. Images of Cherenkov emission have been taken by using a scientific-grade time-gated ICCD camera, synchronized to the LINAC pulse output, during treatment. Sampling depth depending on wavelength and angular distribution of Cherenkov photons (similar to Lambertian distribution) emitted from the surface have been investigated for different optical properties by Monte Carlo simulations in GAMOS and corresponding angular emission corrections have been applied. Registration of the 2-D Cherenkov emission images to 3-D surface profiles measured by motion monitoring system (Catalystâ„¢, C-RAD) has been investigated.

Results:
The images show that superficial dose varies dramatically with complex surface profiles. Imaging of this can be done, with a typical acquisition time of 2 sec, based upon Signal to noise ratio of SNR=30 for a 10 MeV beam, suggesting that near real time surface dosimetry is possible during the treatment time. The spatial resolution achieved here was approximately 1mm.

Conclusion:
Superficial dose can be imaged in real-time directly with a camera, capturing the Cherenkov emitted from the surface of the treatment region during external beam radiotherapy, and these surface dose images could potentially allow real time monitoring, quality assurance and decisions to be made about dose errors in complex treatment areas.

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