LINEAR ACCELERATOR ( LINAC ) IN RADIOTHERAPY

1. LINEAR ACCELERATOR ( LINAC )
IN RADIOTHERAPY
DR. AMAL YOUSIF AL-YASIRI

2. What is LINAC
• A linear accelerator (LINAC) is a device that uses
high Radio-‐Frequency (RF)electromagnetic waves
to accelerate charged particles (i.e.electrons) to
high energies in a linear path, inside a tube-like
structure called the accelerator waveguide.
• LINAC is the device most commonly used for
external beam radiation therapy (radiotherapy) to
treat cancer.

3. How Does it Work
• The linear accelerator uses microwave technology to accelerate electrons
to very high energy (in MeV range) in the accelerator waveguide part.
• The Main Operating Components Of A Medical Linac are
• 1-Injection system electron gun: Electrons are produced by thermionic
emission from a heated cathode .
• 2-RF System : The electrons are accelerated in the accelerating wave
guide using high power RF fields. Which are set up in the accelerating
wave guide by microwave radiation which is produced by microwave
generators that are either magnetrons or klystrons.
• 3-Klystron : Provides the source of microwave power to accelerate the
electrons.
• 4- Electron beam transport: It consists of the evacuated drift tubes and
bending magnets, 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.

6. How Does it Work
• If the electron beam is required for the treatment, then
the high energy electrons beam will be directed to the
patient’s tumor after the beam pass through the scattering
foil to broaden the beam.
• If the photons beam is required for the treatment, then
these energetic electrons will be allowed to collide with a
heavy metal target (Tungsten). As a result of the collisions,
high-energy photons (in MeV range) are produced from
the target. The high energy x-rays will be directed to the
patient’s tumor.
• Electrons or photons beam are shaped as they exit the
machine to conform to the shape of the patient’s tumor.
• Radiation can be delivered to the tumor from any angle by
rotating the gantry and moving the treatment couch.

8. What is LINAC used for
• The linear accelerator is used to treat all
parts/organs of the body.
• It delivers high-energy x-rays or electrons to the
region of the patient's tumor.
• These treatments can be designed in such a way that
they destroy the cancer cells while sparing the
surrounding normal tissue.
• The LINAC is used to treat all body sites, using
conventional techniques, Intensity-Modulated
Radiation Therapy (IMRT), Volumetric Modulated
Arc Therapy (VMAT), Image Guided Radiation
Therapy (IGRT), Stereotactic Radiosurgery (SRS) and
Stereotactic Body Radio Therapy (SBRT).

9. Treatment Planning
• The goal of treatment planning is to maximize
the radiation dose to the tumor while
minimizing the dose to organs at risk.
• The best treatment plan for each patient is
determined by a team consisting of radiation
oncologists, medical physicists, medical
dosimetrist, and radiation therapist, they plan
the appropriate external beam radiotherapy.

12. Treatment by Linac
• Treatment is designed in a way that destroys
the cancer cells while sparing the surrounding
normal tissue
• High energy photons enter the patient's body
and aim to break the DNA in all the cells within
the treatment area
• The normal cells are able to repair themselves
while the cancerous cells are unable to do this
and therefore die

13. Treatment by Linac
 Patient lies on a moveable treatment couch
which can move in any direction.
 The X-ray beam comes out of a gantry, which
can be rotated around the patient.
 Radiation is delivered to the tumor from any
angle by rotating the gantry and moving the
treatment couch.

15. Information Flow in Radiotherapy