This document provides an overview of external beam radiation therapy (EBRT) and linear accelerators used to deliver EBRT. It defines EBRT as radiation coming from a machine outside the body that is focused on the cancer. Linear accelerators are described as the most common device for EBRT, using radiofrequency waves to accelerate electrons that produce high-energy x-ray beams targeted at the tumor. Key components of linear accelerators are discussed, including the gantry, treatment head, and safety considerations.

1. Lecture 2
External Beam Therapy (EBT)

2. Most people think of radiation therapy as coming from a
machine outside of the body, but radiation therapy can be
given in a number of ways. Sometimes radiation is given
more than one way at the same time, or different types of
radiation may be given one after the other. Some ways
radiation can be given include:
1- Eternal radiation therapy
2- Internal radiation therapy

3. Lecture 2

4. External radiation therapy

5. Definition of External beam radiation
(EBRT)
External beam therapy (EBT), also called external
radiation therapy,
External beam radiation (EBRT) is the most widely
used type of radiation therapy, and it most often
uses photon beams.
The radiation comes from a machine outside the
body and is focused on the cancer. (EBRT) is a
major treatment modality in radiation therapy.

6. Definition of External beam radiation
(EBRT)
• It utilizes ionizing radiation sources outside a patient’s body to treat
(mostly) malignant conditions in the patient.
• Ionizing radiations used in EBRT include photons, electrons, protons,
neutrons, and heavy ions.
• External photon beam radiotherapy is usually carried out with more
than one radiation beam in order to achieve a uniform dose
distribution inside the target volume and an as low as possible a
dose in healthy tissues surrounding the target. ICRU International
Commission on Radiation unit Report No. 50 recommends a target
dose uniformity within +7% and –5% of the dose delivered to a well
defined prescription point within the target

7. Treatment machines for external beam
radiotherapy

8. introduction

9. Introduction
The study and use of ionizing radiation in medicine
started with three important discoveries:
• X rays by Wilhelm Roentgen in 1895.
• Natural radioactivity by Henri Becquerel in 1896.
• Radium-226 by Pierre and Marie Curie in 1898.

10. Introduction
• The invention of the 60Co
teletherapy unit by H.E. Johns
in Canada in the early 1950s
provided a tremendous boost in
the quest for higher photon
energies and placed the cobalt
unit at the forefront of
radiotherapy for a number of
years.
• Most modern cobalt therapy
machines are arranged on a
gantry so that the source may
rotate about a horizontal axis
referred to as the machine
isocentre axis.

11. Introduction
• Development of medical accelerator
eclipsed cobalt units and became the most
widely used as a radiation source (photons
& electrons)in modern radiotherapy, as it
cover a wide range of energies.
• More exotic particles, such as protons,
neutrons, heavy ions and negative, all
produced by special accelerators, are also
sometimes used for radiotherapy.

12. X RAY BEAMS AND X RAY UNITS

13. X RAY BEAMS AND X RAY UNITS
Clinical X ray beams typically range in energy between 10
kV and 50 MV and are produced when electrons with
kinetic energies between 10 keV and 50 MeV are
decelerated in special metallic targets.
In the target most of the electron’s kinetic energy is
transformed into heat, and a small fraction of the kinetic
energy is emitted in the form of x ray photons which are
divided into two categories:
• Characteristic x rays
• Bremsstrahlung photons

14. • Result from Coulomb interactions between the incident
electrons and atomic orbital electrons of the target
material (collision loss).
• In a given Coulomb interaction between the incident
electron and an orbital electron, the orbital electron is
ejected from its shell and an electron from a higher level
shell fills the resulting orbital vacancy.
• The energy difference between the two shells may either
be
A. Emitted from the atom in the form of a characteristic
photon (characteristic X ray) or
B. Transferred to an orbital electron that is ejected from
the atom as an Auger electron.
1- Characteristic X rays

15. 2. Bremsstrahlung (continuous) X rays
• Bremsstrahlung X rays result from Coulomb
interactions between the incident electron and the
nuclei of the target material.
• During the Coulomb interaction between the
incident electron and the nucleus, the incident
electron is decelerated and loses part of its kinetic
energy in the form of bremsstrahlung photons .
• The bremsstrahlung spectrum produced in a given
X ray target depends on: the kinetic energy of the
incident electron as well as on the thickness and
atomic number Z of the target.

16. X rays are used in diagnostic radiology for diagnosis
of disease and in radiation oncology (radiotherapy)
for treatment of disease.
Superficial X rays,
X rays produced by electrons with kinetic energies
between 10 keV and 100 keV .
Orthovoltage
X rays produced by electrons with kinetic energies
between 100 keV and500 keV .
Megavoltage X rays
X rays produced by electrons with kinetic energies
above 1 MeV.
Clinical X ray beams

17. Superficial and orthovoltage X rays are produced
with X ray tubes(machines),
while megavoltage X rays are most commonly
produced with linacs and sometimes with betatrons
and microtrons.

18. X ray machines for radiotherapy
Superficial and orthovoltage X rays used in radiotherapy are
produced with X ray machines.
The main components of a radiotherapeutic X ray machine
are
 X-ray tube
 Target cooling system
 Control console
 X-ray power generator

20. Medical Linear Accelerators in
Radiation Therapy

21. introduction

24. What is a Linear Accelerator?
• A linear accelerator is a device that uses high
Radio-Frequency (RF)electromagnetic waves to
accelerate charged particle (i.e. electrons) to high
energies in a linear path, inside a tube like
structure called the accelerator waveguide.
• This is the most common device to treat cancer
with external beam radiation.

25. How does it work?
• The linear accelerator (Linac), uses microwave
technology to accelerate electrons in a part of the linac
called waveguide, then allows these electrons to
collide with a heavy metal target. As a result of these
collisions, high energy X-Rays (Photons) are produced
from the target.
• These high energy photons will be directed to the
patient's tumor and shaped as they exit the linac to
conform to the shape of the tumor. •
• Radiation can be delivered to the tumor from any angle
by rotating the gantry and moving the treatment
couch.

29. Linac generations:
• During the past 40 years, medical linacs have gone through five
distinct generations, each one increasingly more sophisticated:
1. Low energy x rays (4-6 MV).
2. Medium energy x rays (10-15 MV) and electrons.
3. High energy x rays (18-25 MV) and electrons.
4. High energy photons and electrons: computer controlled
Operation; dynamic wedge; electronic portal imaging
device (EPID); multileaf collimator (MLC).
5. High energy photons and electrons: photon beam intensity
modulation with MLC; full dynamic conformal dose delivery
with intensity modulated beams produced with an MLC.

30. Safety of linac installations
The complexity of modern linacs raises concerns as to safety of
operation from the point of view of patients and operators. The
International Electro technical Commission (IEC) document addresses
three categories of safety issues
1. Mechanical
2. Electrical
3. Radiation
And establishes specific requirements mainly for the manufacturers
of linacs in the design and construction of linacsfor use in
radiotherapy. It also covers some radiation safety aspects of linac
installation in customer’s treatment rooms.

31. Components of modern linacs
Linacs are usually mounted isocentrically and the
operational systems are distributed over five
major and distinct sections of the machine, the:
● Gantry;
● Gantry stand or support;
● Modulator and power supply
● Patient support assembly (i.e. treatment table);
● Control console.

33. Gantry:

34. Helps direct the X-ray (photons) or electron beams to the
tumor.
• It rotates 360 degrees around a line/point, called the
Isocenter.
• The gantry has the following components:
1. Electron Gun
2. Accelerator guide.
3. Treatment Head.
Gantry:

50. Schematic of the treatment head of a modern linear accelerator
operating in photon-production mode (A) or electron-production
mode (B).

51. Q1 : Choose the correct answer
The machine used for radiotherapy is called as _________
a) Therapeutic X – Ray machine
b) Linear Accelerator
c) Radioactive Ultrasound Machine
-------- result from Coulomb interactions between the incident electron and the nuclei of
the target material
a) Characteristic x-ray
b) Gamma Rays
c) Bremsstrahlung Radiation
The radiation comes from a machine outside the body and is focused on the cancer called
a) External radiotherapy
b) Internal radiotherapy
c) Thermotherapy
Result from Coulomb interactions between the incident electrons and atomic orbital
electrons of the target material
a) Characteristic x-ray
b) Gamma Rays
c) Bremsstrahlung Radiation

52. Question 2: Write the suitable expression for the following definition:
• A. The main components of a radiotherapeutic X ray machine are
1-………………
2-…………………..
3-…………………..
4-………………….
• X ray target depends on ………………….., ……………….,……………..
• Ionizing radiations used in EBRT include …………., ………., ……………., ……….., and ……………….
• The radiation comes from a machine outside the body and is focused on the cancer called
………………………..
……………………………… result from Coulomb interactions between the incident electrons
and atomic orbital electrons of the target material.
• The kinetic energy is emitted in the form of x ray photons which are divided into two
categories: …………………………………….. ,…………………………………………
• ICRU International Commission on Radiation unit Report No. 50 recommends a target dose
uniformity within ……..% and ………% of the dose delivered to a well defined prescription
point within the target.
• Transferred to an orbital electron that is ejected from the atom as an ………………..
• ………………..result from Coulomb interactions between the incident electron and the nuclei
of the target material.

53. • A. International Electro technical Commission (IEC) document addresses three
categories of safety issues
……………..
………………
……………..
• ................Helps direct the X-ray (photons) or electron beams to the tumor.
• The main components of Gantry in LINAC are
………………….
…………………..
…………………..
• D. ………………It is responsible for producing electrons and injecting them into the
accelerator structure.
• E. ……………….. Changes the direction of the electron beam, downwards toward the
patient .
• F. ………………. is required to create a flattened beam of sufficient area, uniformity and
symmetry

54. Question 3: Explain The Following
1. Superficial X rays,
2. Orthovoltage
3. Megavoltage X rays
4. EBRT
5. Linear Accelerator and How does it work?
6. Linear generation
7. Components of modern linacs
8. Treatment head of linacs and component it
9. beam flatting filter and scattering foil

55. Question4 : Arrange the given words on the suitable space of the following figure?
(Gantry, electron gun, , stand , Isocenter, treatment table, Accelerating wave , X-ray
target, electron beam transport and RF Power generation)

56. Use some videos to explain the linear
accelerator
• https://www.youtube.com/watch?v=jSgnWfb
Ex1A
• https://www.youtube.com/watch?v=lZ9cGVax
Oes
• https://www.youtube.com/watch?v=hy9atKA
qAf4&list=PLk59CaRJX5aZWsX5hyLmQQNGfKE
H5iY-J&index=3

57. Thank you for your attention