Principles and Practice of Radiation Therapy Chapter 7 Treatment Delivery Equipment Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Objectives Discuss the historical development of radiation therapy treatment delivery equipment Compare and contrast the clinical applications of kilovoltage equipment, including Grenz-ray therapy, contact therapy, superficial treatments, and orthovoltage therapy Describe the four major components of the linear accelerator stand, including the klystron, waveguide, circulator, and cooling system Explain how x-rays are produced in the linear accelerator Describe the major components located in the gantry of the linear accelerator, including the electron gun, accelerator structure (guide), and treatment head Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Objectives Explain the concept of indexing as it relates to patient immobilization and positioning Identify where multileaf collimators (MLCs) are located in the treatment head and explain how they operate Compare and contrast the use of older equipment such as the betatron, Van de Graaff generator, and cobalt unit Discuss the characteristics of cobalt-60 Describe emergency procedures related to a cobalt-60 source that fails to retract Discuss medical accelerator safety considerations Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Historical Overview 1895 – Discovery of x-rays by Wilhelm Conrad Roentgen Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Equipment Development Kilovoltage units used since the turn of 20th century Units include Grenz Contact Superficial Orthovoltage Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Limitations of Kilovoltage Units Cannot reach deep-seated malignancy No skin sparing Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Equipment Development Megavoltage equipment 1937 Van de Graaff 1941 Betatron 1951 Cobalt units 1952 Linear accelerators Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Grenz Ray 1923 Gustav Bucky constructed tube Less than 20 kV X-ray tube with a lithium borate window Transmitted long wavelength Grenz German for “border” Rays lie in gray zone between x-ray and ultraviolet Inherent filtration 0.1 mm aluminum Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Grenz Ray and Superficial Similarities Envelope is glass Window beryllium Inherent filtration approximately 0.1 mm Quality measure in half-value layer expressed in millimeters of aluminum Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Grenz Ray Applications 200 R per session Effective for the treatment of Inflammatory disorders Bowen’s disease Herpes simplex Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Contact Therapy 40-50 kV Half-value layer of 1 or 2 mm Tube designed so that surface is in contact with housing only 2 cm from target Low energy, short distance, decrease in depth dose Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Contact Therapy Suitable for treatment on surface lesions only Papillon criteria for rectal lesions 3 x 5 cm mobile lesion 4 treatments of 3000 cGy each at 2-week intervals Desirable treatment to preserve anal sphincter Chaoul used contact for hemangiomas 300-500 R Total dose 1200-1500 R Use decreased in 1975 Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Superficial Therapy Units 50-150 kV Half-value layers range from 1 to 6 μm of aluminum to harden the beam Cones used to collimate the beam Surface in contact with cone Source-skin distance (SSD) 15-20 cm Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Orthovoltage Unit 150-500 kV 200-350 kV most commonly used For many years provided the most penetrating beams Called deep therapy SSD 50 cm Still used for skin lesions Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Megavoltage 1 MV or higher Van de Graaff Betatron Cyclotron Linear accelerator Called direct accelerator Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Linear Accelerator Accelerator structure allows electrons to accelerate in straight path Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Early Accelerators Early linear accelerators were large and bulky compared with today’s accelerators First linear accelerator installed in 1952 in Hammersmith Hospital in London First linear accelerator installed in US at Stanford University Treated first patient in 1956 Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Second-Generation Accelerators The older 360-degree rotational units (isocentric) Resulting in improved accuracy and dose delivery Less sophisticated than today’s units Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

First Clinical Linear Accelerator Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Third-Generation Accelerators Computer driven Wide variety of options Dual photon energies Multileaf collimators Several electron energies Electronic portal verification systems Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Linear Accelerator Components Drive stand Gantry Treatment couch Console electronic cabinet Some have a modulator cabinet Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Drive Stand The gantry rotates on a horizontal axis on bearings within the drive stand Four major components are housed in the drive stand: Klystron Circulator Waveguide Water cooling system Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Klystron Source of microwave power Used to accelerate electrons Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Circulator Acts like a valve Receives microwave power from klystron Directs radiofrequency energy into the waveguide Prevents microwaves from returning to the klystron Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Waveguide Hollow, tubelike structure Conveys the microwave power to the accelerator structure in the gantry Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Water Cooling System Maintains constant temperature Cools various components Accelerator structure Klystron Circulator Target Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Gantry Directs the beam at a patient’s tumor The electron gun Produces electrons Injects them into the accelerator structure Cathode made of tungsten The accelerator guide Mounted horizontally (high-energy machines) Mounted vertically (low-energy machines) Receives the microwave power and combines that power with the injected electrons to accelerate the electrons to nearly the speed of light Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Treatment Head For photon therapy Bending magnet X-ray target Primary collimator Beam-flattening filter Ion chamber Secondary collimators Accessory tray for blocks and wedges Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Bending Magnet May bend the electron group through a net angle of approximately 90-270 degrees and onto the x-ray target or scattering foil Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Beam-Flattening Filter Located on the carousel with the scattering foil Shapes the x-ray beam in its cross-sectional dimension Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Scattering Foils Located on the carousel with the flattening filter Spreads out the small, pencil-like beam of electrons and provides a flat, uniform electron treatment field Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Dual Ion Chambers Monitors/samples the beam for its symmetry in the right-left and inferior-superior direction Produces electrical signals that terminate the beam when the prescribed dose is given Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Secondary Collimation Control by using the setting knobs at the collimator head or pendant to adjust the upper and lower collimator jaws MLCs or Cerrobend blocking may further define field Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Field Light Located in the treatment head Simulates the field by illuminating the area Light from a quartz-iodine bulb Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Control Console Located outside the treatment room Controls linear accelerator Digital display, push-button panel, or video display terminal Prescribed dose (monitor units), mechanical beam parameters, and other status messages Interlock system Patient-protection interlocks, beam energy, beam symmetry, dose, radiation, and mechanical hazards Emergency off buttons Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Treatment Couch The treatment couch may also be referred to as the “tabletop” or “patient support assembly” (PSA) Many tabletops support up to 300 pounds and range in width from 45 to 50 cm Indexed carbon fiber couch Patient is indexed and locked into place on treatment table Ensures patient is in same position on table Carbon fiber reduces scatter Helpful in intensity modulated radiation therapy (IMRT) Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Modulator Cabinet Contains three major components Fan control (to cool the power distribution compartment) Auxiliary power-distribution system Primary power-distribution system Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

State-of-the-Art Technologies Allow better beam shaping and dose escalation Types Conformal radiation therapy Dynamic wedging Independent jaws MLCs Electron portal imaging Image-guided radiation therapy (IGRT) Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Dynamic Wedge Modifies and shapes desired isodose distribution Replaces hard wedges Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Multileaf Collimator (MLC) 52-160 leaves Located below secondary collimation The computer-driven, heavy, metal collimator rods slide into place to form field shape MLCs can move during treatment Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Multileaf Collimator (MLC) Two concerns Penumbra at the end of leaves Interleaf transmission leakage 2.5% to 4% Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Electron Portal Imaging Device (EPID) Amorphous silicon imaging technology Images reviewed immediately online Reduce image-receptor distance for better image quality Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Image-Guided Radiation Therapy (IGRT) Image the patient just before treatment and compare the position of the patient to the plan Different forms EPID In-room computed tomography (CT) scanner KV cone-beam CT MV cone-beam CT Ultrasound Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Verification and Recording Devices Allow verification of setup parameters Computer-assisted setup Recording of patient data Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Medical Accelerator Safety Considerations Emergency procedures Written polices should be at or near treatment control console Radiation therapists should be familiar with policies Knowing location of emergency stop buttons is critical Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Medical Accelerator Safety Considerations Electrical Mechanical Radiation safety considerations Misadministration Incorrect application or delivery of prescribed dose Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Medical Accelerator Hazards Type Cause Consequences Incorrect dose delivered Electrical, software, and therapist Serious injury, increased complications, genetic effects, second primary, and compromised tumor control Dose delivered to the wrong area Mechanical, software, patient motion, and therapist Machine Mechanical, collision software, patient motion, and therapist Significant injury and death Incorrect beam Serious injury, increased complications, genetic effects, second primary, and compromised tumor control General hazards Electrical and mechanical Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Betatron Developed by Kerst in 1941 Produces x-rays of 2 MV Circular orbit (doughnut shape) Electron in a changing magnetic field experiences acceleration {COMP: Insert Figure 7-13} Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Van de Graaff 1937 RJ Van de Graaff developed first electrostatic generator Produce high-energy x-rays (2 MV) Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Cobalt Unit Mainstay of departments until the linear accelerator First practical radiation therapy treatment unit to provide Dmax below the skin surface Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Cobalt-60 Production Artificially produced isotope Cobalt-59 is made radioactive in a particle accelerator Source placed in steel capsule with double weld This absorbs beta particles produced during the decay process Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Cobalt Characteristics Emits beta particle with energy of 0.31 MeV Absorbed by steel capsule Nickel-60 results Two gamma rays emitted 1.17 MeV 1.33 MeV Average energy 1.25 MeV Half-life 5.26 years Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Cobalt Characteristics Correction factor of 1% per month must be applied to the output Replace source every 5.3 years Penumbra Area where dose rate changes rapidly Edge of the field Large penumbra on cobalt because of its large source size Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Cobalt Machine Design Source positioning Most common is air-pressure piston Air pressure pushes cobalt source into the on position Travel time Time added to treatment dose to allow for source to travel into position 0.2 second Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Cobalt Shielding Source head contains the source Steel shell filled with lead Housing may be up to 2 feet in diameter Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Cobalt Machine Components Interleaf collimator is part of source head Collimator assists in reducing penumbra Trimmers or satellite collimators may further sharpen the beam Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Cobalt Calibration and Leakage Qualified radiation physicist must perform full calibration testing Perform When source is replaced If 5% deviation is noticed during spot check After a major repair is done Monthly Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Cobalt Calibration and Leakage Full calibration may include: Radiation and light field coincidence Timer accuracy Exposure rate or dose rate Accuracy of distance-measuring devices Wipe test, which must be done twice a year Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Cobalt Radiation Monitoring and Light System Light system to show when machine is on and off On console At head of the machine At entrance to the room If the beam is “on,” a red light must be lit If the beam is “off,” a green light must be lit Monitoring system to detect radiation in treatment room Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Emergency Procedures Refer to Box 7-1 on page 155 of the textbook for the procedure for cobalt-60. Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.