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Imaging of Radiation Dose Using Cherenkov Light

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Imaging of Radiation Dose Using Cherenkov Light Imaging of Radiation Dose Using Cherenkov Light Eric Brost1, Yoichi Watanabe1, Fadil Santosa2, Adam Green3 1Department of Radiation Oncology, University of Minnesota 2Institute for Mathematics and it’s Applications, University of Minnesota 3Department of Physics, University of St. Thomas 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 [2] Outline • Background • Related Research • Cherenkov Imaging Dosimetry Cherenkov Radiation Tissue or other medium Production Incident radiation (gamma or electron) Secondary β electron, c/n Index of refraction: Cherenkov Particle velocity: emission o = 43 (2 MV beam in water) 1 Conical emission angle: Ratio of velocity to speed of light: β β Cherenkov Light Characteristics • The number of photons, N, emitted per unit path due to the Cherenkov effect: 1 1 ∝ 1 Lower limit of Cherenkov emission • For a 6 MeV electron beam delivering 100 cGy to water at a rate of 600 MU/min: 1 • 600 photons/electron • 6‐10 photons/electron from surface • 3 x 1011 detectable photons • 8 x 10‐10 Watts Wavelength () [3] Cherenkov Light ‐ Relationship to Dose Water or tissue Incident radiation (gamma or electron) 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% Dose: Number of photons: Correlation ratio: C Glaser, et al. Phys Med Biol. 2014 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 Imaging of Radiation Beams in Water 10x10 cm, 6 MV beam 2D projection of a C‐ 3D reconstruction using in a quinine sulfate treatment plan tomography solution Glaser, et al. Med. Phys. 30 min scan time 30 sec exposure 2014 1 mm resolution Glaser, et al. Optics Letters. 2013 Superficial Dosimetry during Radiation Therapy • 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 Zhang, et. al. Phys. Med. Bio. 2014 Linac Beam CMOS angle Radiation Field size Cherenkov image To computer Superficial Dosimetry during Radiation Therapy • 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 Optical factors = 40% error Jarvis, et. al. Int. Jour. Of Rad. Onc. 2014 • Correlation ratio Beam factors = 5% error 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 Beam factor Angular scattering correction Optical factors Absorption correction e‐ e‐ Monte Carlo Simulations of Cherenkov Generation Gamos was used to determine Ks : 2 Beam size dependence (pencil ‐ 20x20 cm ) o Beam angle (0‐75 ) 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 Primary particles Beam Optical Skin phantom angle phantom (sublayers) Field size Epidermis (2) Dermis (3) Subcutan. (2) • Physics model • Particle source Monte Carlo engine Geant4 • Geometry • Radiological properties • Optical properties • Scoring filters Text-based interface for Geant4 + GAMOS optical High-energy photon transport transport Charged particle generation + Output scoring Cherenkov Dosimetry transport filters light scoring scoring 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 References 1. 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 References 1. http://www.vmoc.com/wp‐content/uploads/2013/04/IMRT‐Machine.jpg 2. https://www.youtube.com/watch?v=X0LXJRyzovU, used with the permission of Jacqueline Andreozzi 3. http://www.scint‐x.com/media/1748/scint_x_technology1.jpg 4. 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? [4] • Luminosity correction?.
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