LINEAR ACCELARATOR
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A linear accelerator is a machine that accelerates charged particles along a linear path to deliver radiation therapy for cancer treatment. It consists of an electron gun that produces electrons, an accelerator structure that accelerates the electrons using microwaves, and a treatment head that shapes and monitors the x-ray beam. Key components include the gantry that directs the beam, flattening filters and collimators that shape the beam, and ionization chambers that monitor the dose. The linear accelerator accelerates electrons to produce x-rays that are precisely aimed at the tumor to destroy cancer cells while minimizing damage to healthy tissue.
LINEAR ACCELARATOR
- 2. INTROUDUCTION: • A linear accelerator is a machine that accelerate the charge particle to higher energy in to the linear path. • LINAC therapy allows to deliver higher doses of radiation to the tumor with limited damage to the surrounding healthy tissue and/or organs • Uses higher energies for the treatment of cancer patients.
- 4. Vertical mounting (LINAC 1 at AKUH)
- 5. Horizontal Mounting (LINAC 2 at AKUH)
- 6. Auxiliary system: It consist of four system that are not involved in electron acceleration. • A vacuum pumping system producing a vacuum pressure in the accelerating guide and the RF generator. • A water cooling system to accelerating waveguide,RF generator. It provides stable temperature. • Air pressure system. • Shielding against leakage radiation.
- 7. Components: • Modulator cabinet • Console control • Drive stand • Gantry • Treatment couch • Other accessories
- 8. Modulator cabinet: • It distribute primary electrical power and high voltage to magnetron and klystron • it located in treatment room • it major components The fan control: need arises for cooling the power distribution Auxiliary system: contains the emergency off button Primary power dist: Primary power-distribution system
- 9. Console control: • Monitoring and controlling the LINAC • All interlocks checks to allow beam started • Provide digital display of monitor units • Mechanical beam parameters
- 10. Drive Stand: • Klystron/Magnetron: power source used to generate electromagnetic waves for the accelerator guides • Waveguide: hollow tube-like structure that guide the electromagnetic waves from the magnetron to the accelerating guide where electrons are accelerated • Circulator: connects between the klystron/magnetron and waveguide that prevents any reflected microwaves. • Water-cooling system: allows many components in the gantry and drive stand to operate at a constant temperature
- 11. Magnetron: Device that provides high- frequency microwave Accelerate the electrons into the accelerating waveguide. Preferred for lower energies <=6 Source of microwave about 3000 MHZ
- 12. Klystron: • Source of microwave radio frequency RF • Also microwave amplifier • To accelerate the electron into waveguide • For megavoltage energies >6MV
- 13. Electron gun: • source of electrons; it is essentially a simple electrostatic accelerator called an electron gun. • Two types of electron gun are in use as sources of electrons in medical linacs. • — Diode type; • — Triode type.
- 14. Beam transport system: To transport electrons from accelerating waveguide to the x-ray target. • Bending magnet 90 degree bending 270 degree bending • Steering coils • Focusing coils
- 15. Diagram:
- 16. Gantry: Responsible for directing the photon (x-ray) energy or electron beam at a patients tumor. • Electron gun: Produce electrons and injects them into the accelerator structure • Accelerator structure: A special type of wave guide in which electrons are accelerated. • Bending magnet. Alter the path of the electrons from waveguide into the x-ray target • Treatment head: Components designed to shape and monitor the treatment beam X-ray target Primary collimator Ion chambers Flattening filters Secondary collimators Field light
- 18. X-ray target: • High z material tungsten • It thickness maximize the x-ray output and minimize electron contamination
- 19. Primary collimators Secondary collimators: • Fixed just beyond the x-ray target • Design to limit maximum field size • It absorbs scatter from the target • Place Away from the x-ray target • Secondary collimators are typically independent jaws • It allow the field to be shaped into a variety of rectangular shapes. • There are two sets of jaws higher jaws (y-axis) lower jaws (x-axis) • independent jaws to perform dynamic wedging.
- 20. Flattening filter : • The flattening filter is a cone shaped • change the beam profile at depth • Absorbs photons on the central axis • Producing a more uniform beam profile at the treatment distance.
- 21. Scattering Foils: • Typically consist of dual lead foils. • To ensure minimize the bremsstrahlung x-rays • narrow beam is usually spread by two scattering foils • This converts the beam from a pencil beam to a usable wide beam
- 23. Ionization chambers: • Ionization chambers embedded in linac clinical x-rays and electrons for dose monitoring for safety of the patients • Two separately ion chambers • It position between the flattening filters or scattering foils and secondary collimators
- 24. Dose monitoring: • For patient safety, the linac have two electrodes to monitor beam output and connected to the counter. • If the primary chamber fails during patient treatment, the secondary chamber will terminate the irradiation. • only a few per cent above the prescribed dose has been delivered. • The beam energy, flatness and symmetry.
- 25. Multi Leaf Collimator (MLC): • Used to define any field shape for radiation beams • The number of leaves in commercial models with 120 leaves (60 pairs) covering fields up to 40 × 40 cm2 • MLCs are becoming valuable in supplying intensity modulated fields in conformal radiotherapy, either in the step and shoot mode or in a continuous dynamic mode.
- 26. Field light and lasers: • It is a Field localizing device. • Used to display the position of the radiation field on the patient skin. • The accuracy of the laser guides in determining isocentre position • Tolerance of laser position is 2 mm
- 27. Other accessories: • Custom Blocks: In the event that MLCs are unable to produce the desired field shape. They are limited by their cost, weight, and time issues • Electron Cone and Electron Cutout: The electron cone attenuates electrons that are scattered outside of the required beam shape before they reach the cutout • Electronic portal imaging: Electronic portal imaging refers to an electronic detector replacing the radiographic film Provides feedback on single-event setup accuracy or observation of treatment in near real-time the patient can be repositioned before treatment takes place.
- 28. Patients supports: • Treatment couch: mounted on a rotational axis around the isocenter Also called patient support assembly (PSA) • Immobilization devices
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