imaging of radiation dose using cherenkov...
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Imaging of Radiation Dose Using Cherenkov Light
Eric Brost1, Yoichi Watanabe1, Fadil Santosa2, Adam Green31Department of Radiation Oncology, University of Minnesota 2Institute for Mathematics and it’s Applications, University of Minnesota3Department of Physics, University of St. Thomas
[2]
Imaging of Cherenkov light during radiation therapy
• Quality assurance• Surface dosimetry• Molecular imaging
Thesis project goals
1. Determination of optical correction factors necessary to perform Cherenkov dosimetry
2. Examine feasibility of Cherenkov imaging on C‐RAD Catalyst system
Outline• Background• Related Research• Cherenkov Imaging Dosimetry
Incident radiation(gamma or electron)
Secondary electron,
c/n
β
1β
βConical emission angle: Ratio of velocity to speed of light:
Cherenkov emission
Cherenkov Radiation Production
Tissue or other medium
Index of refraction:
Particle velocity:
= 43o (2 MV beam in water)
Cherenkov Light Characteristics• The number of photons, N, emitted per unit path due to the Cherenkov effect:
∝ 11 1
• For a 6 MeV electron beam delivering 100 cGy to water at a rate of 600 MU/min: • 600 photons/electron• 6‐10 photons/electron from surface• 3 x 1011 detectable photons• 8 x 10‐10 Watts
1
Wavelength ( )
Lower limit of Cherenkov emission
[3]
Cherenkov Light ‐ Relationship to Dose
Incident radiation(gamma or electron)
Water or tissue
z (mm)
• Mono‐energetic pencil beams, relationship is 1:1 between light emission and dose (<1%)• Poly‐energetic finite beam sizes, error is between 0‐5%
Glaser, et al. Phys Med Biol. 2014
Dose: Number of photons: Correlation ratio: C
Set‐up of Cherenkov Detection• Camera CMOS, CCD not as viable Triggered to linac output
• Target material Water tank or phantom Patient
• Computer Timing, camera, software
• Radiation source Linear accelerator Radiopharmaceutical
Glaser, et. al. Optics Letters. 2013
3D reconstruction using tomography
30 min scan time
1 mm resolutionGlaser, et al. Optics Letters. 2013
2D projection of a C‐treatment planGlaser, et al. Med. Phys. 2014
10x10 cm, 6 MV beam in a quinine sulfate solution30 sec exposure
Imaging of Radiation Beams in Water
• Cherenkov light can be related to dose through light intensity Dose is deposited locally by charged particles Cherenkov photons are generated and scattered via Mie and Rayleigh scattering
• 5% error associated with variations in beam size, angle of incidence, and energy
• 40% error associated with variations in surface geometry, composition, and tissue pigment
Superficial Dosimetry during Radiation Therapy
To computer
Linac
CMOSBeamangle
Radiation Field size
Cherenkovimage
Zhang, et. al. Phys. Med. Bio. 2014
• Dosimetry is not possible with the current state of Cherenkov detection Skin reaction detection MLC motion tracking @ 2.5 fps
• Factors that are needed for absolute dosimetry:• Luminosity correction• Angular scattering correction• Absorption correction
• Correlation ratio
Jarvis, et. al. Int. Jour. Of Rad. Onc. 2014Optical factors = 40% error
Beam factors = 5% error
Superficial Dosimetry during Radiation Therapy
Cherenkov Dosimetry Correction Factors
Dose [Gy] is the dose received at the mean depth Intensity [W] is the number of Cherenkov photons imaged on a pixel C = Correlation ratio [Gy/Cher. photon] for a given beam size, particle, and energy Image luminosity correction Angular scattering correction Absorption correction
e‐ e‐
Optical factorsBeam factor
Monte Carlo Simulations of Cherenkov Generation Gamos was used to determine Ks :
Beam size dependence (pencil ‐ 20x20 cm2) Beam angle (0‐75o) Beam energy and particle type (6‐20 MeV) Mono and poly‐energetic beams Tissue and optical phantom materials
Linac simulations were compared with experiment
Linac
Beamangle
Fieldsize
Primary particlesOpticalphantom
Skin phantom (sublayers)
Epidermis (2)
Subcutan. (2)
Dermis (3)
Output scoring filters
Text-basedinterface for
Geant4 + optical
transport
Monte Carlo engine Geant4
GAMOS
Cherenkovlight scoring
Dosimetry scoring
• Physics model• Particle source• Geometry• Radiological properties• Optical properties• Scoring filters
High-energy photon transport
Charged particle generation +
transport
Optical photon generation +
transport
Optical Phantom Scattering Correction, Ks
1
Stratified Skin Scattering Correction, Ks
1
Summary• Cherenkov light can be related to dose deposition – current measurements have high uncertainty
•
• Monte Carlo simulations were used to find scattering correction factor
Next Steps:
• Solving for and
• Apply formula for skin dosimetry
Acknowledgments
Dr. Yoichi Watanabe
for acting as my advisor in this research
Dr. Adam Green
for his continued guidance and advise throughout the development of this research
References1. Glaser, A. K., Zhang, R., Gladstone, D. J., & Pogue, B. W. (2014). Optical dosimetry of radiotherapy
beams using Cherenkov radiation: The relationship between light emission and dose. Physics in Medicine and Biology Phys. Med. Biol., 59(14), 3789‐3811. doi:10.1088/0031‐9155/59/14/3789
2. Goulet, M., Rilling, M., Gingras, L., Beddar, S., Beaulieu, L., & Archambault, L. (2014). Novel, full 3D scintillation dosimetry using a static plenoptic camera. Med. Phys. Medical Physics, 41(8), 082101. doi:10.1118/1.4884036
3. Glaser, A. K., Voigt, W. H., Davis, S. C., Zhang, R., Gladstone, D. J., & Pogue, B. W. (2013). Three‐dimensional Čerenkov tomography of energy deposition from ionizing radiation beams. Optics Letters Opt. Lett., 38(5), 634. doi:10.1364/ol.38.000634
4. Glaser, A. K., Davis, S. C., Mcclatchy, D. M., Zhang, R., Pogue, B. W., & Gladstone, D. J. (2013). Projection imaging of photon beams by the Čerenkov effect. Med. Phys. Medical Physics, 40(1), 012101. doi:10.1118/1.4770286
5. Zhang, R., Glaser, A. K., Gladstone, D. J., Fox, C. J., & Pogue, B. W. (2013). Superficial dosimetry imaging based on Čerenkov emission for external beam radiotherapy with megavoltage x‐ray beam.Med. Phys. Medical Physics, 40(10), 101914. doi:10.1118/1.4821543
6. Jarvis, L. A., Zhang, R., Gladstone, D. J., Jiang, S., Hitchcock, W., Friedman, O. D., . . . Pogue, B. W. (2014). Cherenkov Video Imaging Allows for the First Visualization of Radiation Therapy in Real Time.International Journal of Radiation Oncology*Biology*Physics, 89(3), 615‐622. doi:10.1016/j.ijrobp.2014.01.046
Image References1. http://www.vmoc.com/wp‐content/uploads/2013/04/IMRT‐Machine.jpg2. https://www.youtube.com/watch?v=X0LXJRyzovU, used with the permission of
Jacqueline Andreozzi3. http://www.scint‐x.com/media/1748/scint_x_technology1.jpg4. http://www.aepint.nl/wp‐content/uploads/2016/01/Catalyst‐HD‐1‐260x220.jpg
C‐RAD Catalyst System
• Optically‐based patient positioning system
• Uses optical triangulation to obtain 3D coordinates of detected surface
• Automatic patient positioning
• Respiratory gating
• Cherenkov detection?
• Luminosity correction? [4]