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RadThera
LINAC
| Question | Answer |
|---|---|
| A device that uses high Radio-Frequency (RF) electromagnet waves to accelerate charged particles (i.e. electrons) to high energies in a linear path, inside the tube like structure called the accelerator waveguide. | Linear Accelerator |
| The resonance cavity frequency of the medical linacs is about ______ Hertz (cycles/sec). | 3 billion |
| PROCESS OF HOW LINAC WORKS 1. Patient lies on a ___ treatment couch which can move in any direction 2. The beam comes out of a part of the accelerator called a ___, which can be rotated around the treatment couch. | moveable: gantry |
| PROCESS OF HOW LINAC WORKS 3. Radiation is delivered to the tumor from any ___ by rotating the gantry and moving the treatment couch | angle |
| DREAMLAND, 2014 - Radiation therapy begins with a linear accelerator, which speeds ___ toward a target to generate a radiation beam aimed at the patient's tumor. | electrons |
| DREAMLAND, 2014 - The ___ _____ shapes the radiation beams and varies their intensity. This enables physicians to target higher radiation doses to the tumor while sparing healthy tissue. | multileaf collimator |
| DREAMLAND, 2014 - The radiation beam is precisely tailored to the ___ of a patient's tumor. This shape changes as radiation is delivered from different angles, so that the tumor is always targeted and healthy tissues are protected | shape: |
| DREAMLAND, 2014 - A ___ ____ uses three-dimensional images of the tumor and surrounding anatomy to optimize a treatment plan for delivering radiation according to the oncologist's specifications. | computer system |
| HOW DOES IT WORK - The LINAC uses __ ___ to accelerate electrons in a part of the accelerator called the "__ ___", then allows these electrons to collide with a heavy metal target. As a result of collisions, ___ ___ photons are produced from the target. | microwave technology : wave guide: high-energy |
| HOW DOES IT WORK - The high energy x-rays will be directed to the px's tumor and shaped as they exit the machine to conform to the shape of the px's ___ . Radiation can be delivered to the tumor from any angle by rotating the ___ and moving the ___ ____. | tumor : gantry : treatment couch |
| ADVANTAGES - Particles are able to reach very high energies without the need for extremely high ___ - Linear accelerators attack the ___ area with higher doses of radiation than other machines | voltages : affected |
| DISADVANTAGES - A linear accelerator can cost anywhere between 1 million and 3 million dollars. Operating the machine cost about ___ dollars annually. - The particles travel in a ___ line. Each accelerating segment is used only once . | 900,000 : straight |
| The Main Operating Components Of A Medical Linac Usually Grouped Into 5 Classes: | 1. Injection system 2. RF system 3. Auxiliary system 4. Beam transport system 5. Beam collimation and Monitoring system |
| - Produces electrons for acceleration? - Uses RF energy to speed up electrons? | Electron Gun Accelerating Wave Guide |
| - Supplies radiofrequency power to the waveguide? - Physically supports the waveguide and RF generator? | RF Power Generator Stand |
| - Rotates around the patient to deliver radiation from multiple angles? - Guides accelerated electrons to the X-ray target? | Gantry Electron Beam Transport |
| - Converts high-energy electrons into therapeutic X-ray? - Central point where radiation beams converge for precise targeting? | X-ray Target Isocenter |
| - Path around which the gantry rotates? - Aligns the treatment couch with the isocentre for accurate delivery? - Where the patient lies; adjustable for optimal positioning? | Gantry axis Couch axis Treatment couch |
| INJECTION SYSTEM - Electrons are produced by___ ___ from a heated cathode. - Two basic types of electron gun exist: | thermionic emission : diode and triode |
| TYPES OF ELECTRON GUN - In the diode gun the voltage applied to the cathode is pulsed, so producing bunches of electrons rather than a continuous stream. | The Diode type |
| TYPES OF ELECTRON GUN - Produces discrete bunches of electron by introducing a grid, between cathode and anode. | The Triode type |
| INJECTION SYSTEM - The injection of electrons into the accelerating waveguide is then controlled by ___ ___, which are applied to the grid and must be synchronized with the pulses applied to the ___ ____. | voltage pulses : microwave generator |
| RF SYSTEM - The electrons are accelerated in the accelerating wave guide using __ ___ ___ __ . Which are set up in the accelerating wave guide by __ radiation. - This radiation is produced by microwave generators that are either __ or __. | high power RF fields : microwave : magnetrons or klystrons |
| WHAT MICROWAVE GENERATOR - It produces microwaves required for electron acceleration. - Function as a high frequency oscillator. - Peak power up to 5 MW. | Magnetrons |
| WHAT MICROWAVE GENERATOR - It acts as a RF power amplifier. - Peak power on the order of 7MW or higher. - Mainly using in high energy linacs | Klystron |
| ELECTRON BEAM TRANSPORT - It consists of the ___ ___ ___ and ___ ___, which are used in transporting the electron beam from the accelerating waveguide to the x ray target or to the exit window for electron beam therapy. | evacuated drift tubes : bending magnets |
| ELECTRON BEAM TRANSPORT -___ and ____ ____ installed on the accelerating wave guide are usually linked with the electron transport system. | Steering and focusing coils |
| Contains components that distribute and monitor primary electrical power and high-voltage pulses to the magnetron or klystron - Is located in the treatment room. - 3 Major components? | Modulator cabinet - fan control, Auxiliary power-distribution system, & Primary power distribution system |
| COMPONENTS OF MODULATOR CABINET - Regulates cooling fans - Prevents overheating of electrical components | Fan control |
| COMPONENTS OF MODULATOR CABINET - Provides low-voltage power to control circuits and support systems - Ensures proper operation of monitoring and safety devices | Auxiliary power-distribution system |
| COMPONENTS OF MODULATOR CABINET - Distributes high-voltage power to the magnetron or klystron - Enables generation of microwave energy for the linear accelerator | Primary power distribution system |
| - Provides a central location for monitoring and controlling the linac - Take the form of a digital display, push button panel or video display terminal (VDT) | Console |
| CONSOLE - All ___ must be satisfied for the machine to allow the beam to be started. - Provides a ___ ___ for prescribe dose (monitor unit), mechanical beam particles such as collimator setting or gantry angle | interlocks : digital display |
| A stand containing the apparatus that drives the linear accelerator - Open on both sides with swinging doors for easy access to gauges, valves, tanks and buttons. | Drive stand |
| Power source use to generate electromagnetic waves for the accelerator guides. | Klystron/Magnetron |
| Hollow tube-like structure that guide the electromagnetic waves from the magnetron to the accelerating guide where electrons are accelerated | Waveguide |
| Directs the RF energy into the waveguide and prevents reflected microwaves from returning to the klystron. | Circulator |
| Allows many components in the gantry and drive stand to operate at a constant temperature | Water-cooling system |
| - Responsible for directing the photon (x-rays) energy or electron beam at a patient tumor. - It rotates 360 degrees around a line/point, called the Isocenter | Gantry |
| - Produce electrons and injects them into the accelerator structure. - A special type of wave guide in which electrons are accelerated. - Components designed to shape and monitor the treatment beam. | Electron gun Accelerator structure Treatment head |
| - Is a mechanically movable motor driven couch. - Patient is positioned over the ___ ___ according to the desired co-ordinates of planning. | Treatment table (couch) |
| Treatment table can be moved ___, _____as well as ____ directions. | horizontal, vertical , rotational |
| Contains all the control switches which can be used to access the movement of Gantry, couch, collimator jaws (field size) SSD etc. | Hand pendant |
| TREATMENT TABLE TRANSLATION RANGES • Vertical movement: ____ to _____ • Horizontal movement (left-right): ____ to _____ • Horizontal movement (forward-backward): ____ to _____ | +25.0mm to -50.0mm +25.0mm to -25.0mm +50.0mm to -50.0mm |
| TREATMENT TABLE ROTATION RANGES | Rotational movement: +/- 3.0° in three axes (pitch, roll, jaw) |
| Bends the electron beam through a right angle, so it ends up pointed at the patient | Bending magnet |
| Bending magnet that have the property that any energy spread results in spatial dispersion of the beam. | 90 degree magnets (chromatic) |
| Bending magnet that is designed to eliminate spatial dispersion | 270 degree magnets (achromatic) |
| 3 SYSTEMS FOR ELECTRON BEAM BENDING - Accelerated Electron Beam - Uniform Magnetic Field - Incoming magnetic field pressure | 90° bending |
| 3 SYSTEMS FOR ELECTRON BEAM BENDING - Accelerated Electron Beam - Target - Curved path - Increased viewing external category | 2. 270° bending |
| 3 SYSTEMS FOR ELECTRON BEAM BENDING - Flight tube - Magnet 1-3 | 112.5° bending (Slalom bend) |
| Thin metal sheets provide electrons with which they can scatter, expanding the useful size of the beam. | Scattering foil |
| Electron and photon beams must first be measured or monitored in order to allow delivery of the prescribed amount of radiation. | Monitor Chambers |
| Calculation of MU for Fixed SSD treatment: | MU = Dose (in cGy) / CF. (PDD. OF. WF) |
| Calculation of MU for Fixed SAD (Isocentric) treatment: | MU = Dose (in cGy) / CF. (TPR. OF. WF) |
| - Machine setting that determines how long radiation is delivered to give the prescribed dose? - Prescribed radiation dose to the treatment point, measured in centigray? | Monitor Units (MU) Dose (cGy) |
| - Converts monitor units to actual dose output of the linear accelerator - Usually expressed as cGy per MU under reference conditions | CF (Calibration Factor) |
| - Percentage of the dose delivered at a specific depth compared to the dose at the surface or maximum depth? - Ratio of dose at a given depth to dose at a reference depth in a phantom (Independent of SSD) | PDD (Percent Depth Dose) (Fixed SSD treatment) TPR (Tissue Phantom Ratio) (Fixed SAD / Isocentric treatment) |
| - Accounts for changes in dose output due to field size? - Accounts for beam attenuation caused by a wedge filter? | OF (Output Factor) WF (Wedge Factor) |
| RADIATION SAFETY/INTERLOCK SYSTEM - Similar to treatment from radiation the safety from radiation also plays an important role in Radiotherapy - Various ___ are present in LINAC to avoid the mis-happens or wrong treatment to the patient. | interlocks |
| RADIATION SAFETY/INTERLOCK SYSTEM - Interlocks indicates the problem in particular device in the ____ _____ and interlocking system helps in solving this particularly and easily. - Examples of safety interlocks include: | LINAC assembly : Last Man Out Switch (LMO), Door Interlock, Beam on/off key |
| RADIATION SAFETY/INTERLOCK SYSTEM - Ensures all personnel have exited the treatment room - Must be activated before radiation can be turned on | Last Man Out Switch (LMO) |
| RADIATION SAFETY/INTERLOCK SYSTEM - Prevents radiation delivery if the treatment room door is open - Automatically stops the beam when the door is opened | Door interlock |
| RADIATION SAFETY/INTERLOCK SYSTEM - Controls authorization to activate the radiation beam - Prevents unauthorized or accidental beam activation | Beam on/off key |
| _____ _____ are provided at all the systems of a LINAC unit with only a single switch during emergencies. | Emergency Switches |
| • Overcomes two problems by making it possible to view the portal images instantaneously: real time images can be displayed on the computer screen before initiating a treatment. - Portal images can also be stored on computer for later viewing/archiving | Electronic Portal Imaging Device (EPID) |
| A ____ converts the radiation beam into visible photons. The light is detected by an array of photo nuclides implanted on an ____ ____ panel. | scintillator : amorphous silicon |
| - Embedded in linac clinical X-rays and electrons for dose monitoring for safety of the patients - Two separate - Its position between the ____ ____ /___ ___ and _____ _____. | Ionization chambers : flattening filters/scattering foils and secondary collimators |
| BEAM MODIFICATION - to eliminate radiation dose to some special parts of the zone at which the beam is directed. | Shielding |
| BEAM MODIFICATION - To allow normal dose distribution data to be applied to the treated zone, when the beam enters a or obliquely through the body or where different types of tissues are present | Compensation |
| BEAM MODIFICATION - Where a special tilt in isodose curves is obtained. | Wedge filtration |
| BEAM MODIFICATION - Where the spatial distribution of the natural beam is altered by reducing the central exposure rate relative to the peripheral. | Flattening |
| Types of Beam Modification Devices | Field blocking and Shaping devices: - Shielding blocks - Custom blocks - Asymmetrical jaws - Multileaf collimators Compensators Beam spoilers Wedge Filters Beam flattening filters Bolus Breast cone Penumbra trimmers Electron beam modification |
| - Protect critical organs - Avoid unnecessary radiation to the surrounding normal tissue - Matching adjacent fields | Shielding |
| An ideal shielding material should have the ff. characteristics: | High Atomic Number High density Easily Available Inexpensive |
| A low-melting-point alloy used mainly in radiation therapy for shielding and beam shaping. | Cenoband (Lipowitz metal) |
| BEAM SHIELDING: COLLIMATORS AND BLOCKS - 4 MV →____ cm - ___ MV → 6.5 cm - 10 MV → ___ cm - Co‑60 (1.25 MeV) →___ cm | 6 6 7 5 |
| - A tissue equivalent material used to reduce the depth of the maximum dose (D_max). - Also called as "_______ _____" | Bolus : build-up bolus |
| - A bolus can be used in place of a _____ for kV radiation to even out the skin surface contours. - In megavoltage radiation bolus is primarily used to bring up the _____ _____ near the skin in treating superficial lesions. | compensator : build- up zone |
| - Particles travel in a circular pattern - The particles travel in a spiral pattern | Betatron Cyclotron |
| High-energy Machines | Van de Graaff generator Betatron Cyclotron Linear accelerator Cobalt unit |
| THE RADIATION THERAPY TEAM | Oncology Nurse Radiation Therapy Technologist Medical Physicist/Dosimetrist Radiation Oncologist Administrative Staff |
| An electrostatic device that uses a moving belt to accumulate high-voltage, low-current electricity on a hollow metal sphere | Van de Graaff generator |
Created by:
yulyae