Imaging of Radiation Dose Using Cherenkov Light

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1 Imaging of Radiation Dose Using Cherenkov Light Eric Brost 1, Yoichi Watanabe 1, Fadil Santosa 2, Adam Green 3 1 Department of Radiation Oncology, University of Minnesota 2 Institute for Mathematics and it s Applications, University of Minnesota 3 Department 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 [2]

3 Outline Background Related Research Cherenkov Imaging Dosimetry

$radiation (gamma or electron) Index of refraction: Particle$ velocity: Secondary electron, c/n β Cherenkov emission = 43 o (2 MV

4 Cherenkov Radiation Production Tissue or other medium Incident radiation (gamma or electron) Index of refraction: Particle velocity: Secondary electron, c/n β Cherenkov emission = 43 o (2 MV beam in water) Conical emission angle: 1 β Ratio of velocity to speed of light: 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

5 Cherenkov Light Characteristics The number of photons, N, emitted per unit path due to the Cherenkov effect: Lower limit of Cherenkov emission 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 detectable photons 8 x Watts 1 Wavelength ( ) [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

6 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% Dose: Number of photons: Correlation ratio: C Glaser, et al. Phys Med Biol. 2014

7 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,

2014 3D reconstruction using tomography 30

8 Imaging of Radiation Beams in Water 10x10 cm, 6 MV beam in a quinine sulfate solution 30 sec exposure 2D projection of a C treatment plan Glaser, et al. Med. Phys D reconstruction using tomography 30 min scan time 1 mm resolution Glaser, et al. Optics Letters. 2013

with variations in beam size, angle of incidence, and energy 40% error associated with variations in surface geometry,

9 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 Linac Zhang, et. al. Phys. Med. Bio Cherenkov image To computer CMOS Beam angle Radiation Field size

10 Superficial Dosimetry during Radiation Therapy Dosimetry is not possible with the current state of Cherenkov detection Skin reaction detection MLC motion 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 Correlation ratio Beam factors = 5% error

11 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

12 Monte Carlo Simulations of Cherenkov Generation Gamos was used to determine K s : Beam size dependence (pencil 20x20 cm 2 ) Beam angle (0 75 o ) 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 Field size Beam angle Primary particles Optical phantom Skin phantom (sublayers) Epidermis (2) Dermis (3) Subcutan. (2)

filters High-energy photon transport Output scoring filters Cherenkov light scoring

13 Physics model Monte Carlo engine Geant4 Particle source Geometry Radiological properties Optical properties Text-based interface for Geant4 + optical transport GAMOS Scoring filters High-energy photon transport Output scoring filters Cherenkov light scoring Dosimetry scoring Charged particle generation + transport Optical photon generation + transport

14 Optical Phantom Scattering Correction, K s 1

15 Stratified Skin Scattering Correction, K s 1

16 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

17 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

18 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), doi: / /59/14/ 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), doi: / Glaser, A. K., Voigt, W. H., Davis, S. C., Zhang, R., Gladstone, D. J., & Pogue, B. W. (2013). Threedimensional Čerenkov tomography of energy deposition from ionizing radiation beams. Optics Letters Opt. Lett., 38(5), 634. doi: /ol 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), doi: / 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), doi: / 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), doi: /j.ijrobp

19 Image References 1. content/uploads/2013/04/imrt Machine.jpg 2. used with the permission of Jacqueline Andreozzi 3. x.com/media/1748/scint_x_technology1.jpg 4. content/uploads/2016/01/catalyst HD 1 260x220.jpg

20 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]

8/3/2016. CAMPEP Accredited, 2016!! CHERENKOV IMAGING IN RADIOTHERAPY: 2D, 3D, REALTIME 3D, Disclosure

8/3/2016. CAMPEP Accredited, 2016!! CHERENKOV IMAGING IN RADIOTHERAPY: 2D, 3D, REALTIME 3D, Disclosure CHERENKOV IMAGING IN RADIOTHERAPY: 2D, 3D, REALTIME 3D, Real time IMRT Real time MRI/Co Whole breast radiotherapy Total skin therapy Brian W. Pogue PhD Engineering, Physics, Surgery, Dartmouth College