An An Over erview of Ra Radiation T Therapy Kirk Bertsche, Accuray, Inc. For the 2018 Annual Meeting of the American Scientific Affiliation 1
Ca Cancer Facts • Leading cause of death worldwide • 40% in this room will be diagnosed with cancer • >1.7 million new cancer cases in the US annually • Men: if live long enough, will get prostrate cancer • 2/3 of cancer patients will have radiation therapy (RT) • >40% of those cured will be cured with RT 2
Ca Cancer 5-yr yr Prevalence, , per 100,0 ,000 3
Cancer Statistics, North America 4
Ca Cancer and Ra Radiation on Therapy (RT) • What is CANCER? • Uncontrolled, rapid cell division • What is RADIATION THERAPY (RT)? • Therapeutic use of ionizing radiation • Kills cells and/or halts reproduction • How did RT begin? 5
Di Discovery o of X X-Ra Rays: Wilhelm m Roe oentgen, 1895 Early X-ray tube used by Crookes tube Roentgen, c. 1896 (D-Kuru/Wikimedia Commons) (Smithsonian National Museum of American History) • Discovered X-rays in experiments with early cathode-ray tubes • Awarded first Nobel Prize in Physics, 1901. 6
X-Ra Rays for or Ra Radiation on Therapy: 1896 • X-ray treatments within 1 year of discovery! • Leopold Freund: RT for hairy moles on 5 year old girl. • Victor Despeignes: RT for stomach cancer. • Emil Grubbe: RT for breast cancer. • No understanding of physics or biology of X-rays Early X-ray RT for epithelioma of the face (Sinclair Tousey, 1915. Medical electricity..., Saunders) 7
Di Discovery o of R Radioact ctive M Materi rials: H : Henri ri Becquerel, 1896 Be Henri Becquerel Marie & Pierre Curie • Becquerel discovered radioactivity in 1896 in uranium salts. • Becquerel’s student, Marie Curie, with husband Pierre, discovered polonium and radium in 1898. • All three shared third Nobel Prize in Physics, 1903. 8
Ra Radium m RT befor ore Wor orld War II • 1901: Radium therapy begins • 1911: Claudius Regaud begins introducing low dose rate and fractionated therapy with radium • Radium use gradually declines due to cost J. Murdoch, British Journal of Radiology 1931 9 4(42): 256-284
Ot Othe her Uses for Radium dium 10
X-Ra Ray RT befor ore Wor orld War II Coolidge-type tube • 1916: “Orthovoltage” (50- with water cooling 500 kV) RT using hot cathode added X-ray tubes invented by William Coolidge at GE • 1937: “Megavoltage” (>1 MV) RT using 1.2 MV Van de Graaff driven X-ray tube in Boston Van de Graaff driven X-ray tube for RT 11
X-Ra Ray RT after Wor orld War II • RF linear electron Fry’s 8 MeV linac at Hammersmith accelerators (linacs) enabled Hospital, London by WW2 advances in radar (P. Howard-Flanders (1954) Acta Radiologica and microwaves 41 :sup116, 649-655.) • 1953: D.W. Fry’s 8 MeV travelling- wave (TW) linac used for RT at Hammersmith Hospital, London Kaplan & • 1956: Henry Kaplan & Ed Ginzton’s Ginzton’s 6 MeV 6 MeV TW linac used for RT at linac at Stanford-Lane Hospital, San Stanford-Lane Francisco Hospital, San Francisco (Stanford Report, April 18, 2007) 12
Ot Othe her RT T Develo lopm pments • 1938: Neutron therapy with 37-inch cyclotron, Berkeley • 1949: X-Ray RT with 20 MeV betatron at U Illinois • 1951: Harold Johns begins RT with cobalt-60 • 1954: Proton therapy begins at 184-inch cyclotron, Berkeley • 1957: Particle therapy (He ion) begins, Berkeley 13
Mod Modern Me Medical Linacs for or RT Varian TrueBeam Elekta Synergy Accuray RadiXact Accuray CyberKnife 14
Ho How D w Does es A An R RF L F Lin inac ac W Work? • RF (Microwave) Power • Electron Source • Electron Acceleration • X-Ray Production 15
RF Power RF Linac Block Diagram Microwave • Microwave Power Source Power Source Circulator • Magnetron (or Klystron) • 3 or 9 GHz High-Power Tuning • 1-6 MW peak, 1-6 kW avg Load Motor • RF Circulator • Protects source from power reflecting from linac Load • Electron Linac • Automatic Frequency Control (AFC) • Tracks source frequency to resonant frequency of linac AFC Circuit 16 Part #
RF RF Power Sou ources Magnetron : High-Power Microwave Oscillator Klystron: High-Power Microwave Amplifier • Electrons orbit in uniform axial magnetic field • Electrons excite oscillations in resonant cavities (Charly Whisky at English Wikipedia) • Electron velocity is modulated • Cavities radiate http://hyperphysics.phy- in buncher cavity microwave power astr.gsu.edu/hbase/waves/magnetron.html • Electron density becomes • Microwave power modulated downstream is transmitted to • Modulations excite oscillations linac in output cavity 17
El Electron n Sour urce (“Gun”) un”) Filament Electrons Anode Grid Cathode http://www2.l-3com.com/edd/products/r_linear.htm • Cathode: -9kV to -15 kV (typ) • Filament heats cathode • (Optional) grid controls gun current 18 Part #
Electron El n Acceleration Ba Basic Pillbox RF Ca Cavity • Hollow “pillbox”-shaped conductive cavity has electromagnetic standing- wave resonant modes • If L<2R, lowest frequency resonant mode is TM 010 mode (shown) c c w = » J 2 . 405 TM 0 , 1 R R 010 w æ ö = ç ÷ E z ( r ) E J r 0 0 è c ø http://uspas.fnal.gov/materials/09UNM/Unit_4_Lecture_9_RF_Cavities.pdf 19 Part #
El Electron n Acceleration Pr Practica cal RF Cavities for Linacs • Add holes on axis for beam to pass through • Add “noses” to concentrate E z E z along beam • Round outside corners to reduce power loss http://uspas.fnal.gov/materials/09UNM/Unit_4_Lecture_9_RF_Cavities.pdf 20
El Electron n Acceleration p /2 Co Coupled Ca Cavity y Mode (idea due to Knapp et al at LANL in 1960s) E.A. Knapp, “High Energy Structures”, in Linear Accelerators, ed. P.M. LaPostolle and A.L. Septier, p. 607. 21
El Electron n Acceleration • Wave “Surfing” • Bunching • Focusing http://www.particleadventure.org/accel_particles.html 22
Va Varian System • Gantry rotates around patient • Horizontal linac • Bend magnet 23
Cy CyberKnife X-Ra Ray Head Transmission Waveguide Electron Source (Gun) • Linac and RF components are mounted in linac head Circulator at end of robotic arm Target • MLC = Multi-Leaf Collimator Primary Collimator Magnetron Pulse Transformer (not shown) MLC Standing Wave Linac
X-Ra Ray Prod oduction on Br Bremsstrahlung Photon spectrum: 6 MeV avg, 6.7 MeV max electrons on tungsten target • Relativistic electrons strike dense (hi-Z) material • Deceleration near atomic nuclei produces Bremsstrahlung = “Braking radiation” (high-energy X-rays) 25
X-Ra Ray Prod oduction on Co Collimation • High-energy X-ray/ g -ray beam is masked by high-Z collimator • Most modern systems offer a multi-leaf collimator (MLC) to conform radiation shape to tumor 26
En Energy Deposit itio ion vs. Depth 1 0.8 0.6 PDD 0.4 0.2 0 0 50 100 150 200 250 300 Depth (mm) • Energy deposition (Dose) drops off with depth, due to absorption and scattering • So how do we kill a deep tumor without killing good tissue? 27
Mod Modern Treatme ment Planning • Use beams from multiple “ports” to overlap on tumor • Shape beams with MLC (3D Conformal RT) • Modulate beam intensity (IMRT) • Image guidance (IGRT) allows “4D” RT • Prostate, e.g. • Limit dose to good tissue, especially to rectum and heads 7 beam IMRT prostate treatment plan of femurs (http://karenkrueger.weebly.com/) 28
Ne New Trends and De Develop opments • Better treatment plans • Faster computers, improved algorithms • Better imaging • Most systems now incorporate diagnostic X-rays • Incorporation of MRI, PET, ultrasound • Allow motion tracking (https://youtu.be/dbM2b6vTGb8) • “Flash” • Very high dose rate may be beneficial (300x normal!) • Radiosensitizers • Particle therapy • Protons, ions • Takes advantage of “Bragg peak” 29
Br Bragg Peak in Particle Therapy • Bragg peak--sharp distal edge • Particles also give sharper lateral edges • Usually need to spread out the peak 30
Su Summary • Radiation therapy is beneficial in treating cancer • A number of disciplines together enable radiation therapy • Basic physics (electromagnetism, relativity, quantum mechanics) • Applied physics and engineering (particle accelerator design, high power microwave components, high vacuum systems) • Medical physics • New developments will continue to improve radiation therapy • Radiation therapy enables us, created in the imago dei, to better exercise dominion over disease and to help subdue it (Gen 1:26-28) 31
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