2. People with cancer have several treatment options
but this is depending on the tumor type and stage
of the cancer, patients may be treated with surgery,
radiation therapy, or chemotherapy. Some patients
receive a combination of treatments.
Introduction to Radiation Oncology
4. Definition of Radiation
• “Radiation is an energy in the form of electro-
magnetic waves or particulate matter, traveling in
• In physics, radiation is the emission or transmission
of energy in the form of waves or particles through
space or through a material medium. This includes:
electromagnetic radiation, such as radio waves,
microwaves, infrared, visible light, ultraviolet, x-
rays, and gamma radiation (γ
5. Classification of radiation
• As shown in Fig. radiation is classified into
two main categories, nonionizing
• and ionizing, depending on its ability to ionize
6. Non-ionizing radiation (cannot ionize matter).
Non-ionizing (or non-ionising) radiation refers to any type
of electromagnetic radiation that does not carry
enough energy per quantum (photon energy) to ionize atoms or
molecules, It includes electric and magnetic fields, radio waves,
microwaves, infrared and ultraviolet.
Ionizing radiation (can ionize matter either directly or indirectly):
1- Directly ionizing radiation (charged particles): electrons, protons, a
particles and heavy ions.
Directly ionizing radiation deposits energy in the medium through
direct Coulomb interactions between the directly ionizing charged
particle and orbital electrons of atoms in the medium.
7. 2- Indirectly ionizing radiation (neutral particles): photons (X
rays and gamma rays), neutrons.
Indirectly ionizing radiation (photons or neutrons) deposits
energy in the medium through a two step process:
● In the first step a charged particle is released in the medium
(photons release electrons or positrons, neutrons release
protons or heavier ions);
● In the second step the released charged particles deposit
energy to the medium through direct Coulomb interactions
with orbital electrons of the atoms in the medium.
8. Gamma rays and X rays
Gamma rays can be emitted from the nucleus of an atom
during radioactive decay. They are able to travel tens of
yards, or more, in air, and can easily penetrate the human
body. Shielding this very penetrating type of ionizing
radiation requires thick dense material such as several
inches of lead or concrete
so g rays: resulting from nuclear transitions.
X-rays are photons, like visible light, photons have enough
energy to cause ionization.
Characteristic X rays: resulting from electron transitions
between atomic shells.
It is produced when inner-shell electrons of the anode
target are ejected by the incident electrons.
To eject a bound atomic electron, the incident electron must
have energy greater than the binding energy.
11. The resultant vacancy is filled by an outer-shell electron,
and the energy difference is emitted as characteristic
radiation (e.g., K-shell x-rays, L-shell x-rays), as shown in
12. Bremsstrahlung: resulting from electron–nucleus Coulomb
when incident electrons interact with nuclear electric fields, which
slow them down (brake) and change their direction.
Bremsstrahlung (braking) x-rays are produced
X rays and gamma rays have essentially the same properties
but differ in origin.
X rays are emitted from processes outside the nucleus, while
gamma rays originate inside the nucleus.
X rays are generally lower in energy and are less penetrating
than gamma rays
14. Types of photon interaction
Photons may undergo various possible interactions with
the atoms of an attenuator; the probability or cross-
section for each interaction depends on the
energy of the photon and on the atomic number Z of
The X-ray and γ ray photons lose their energy these major
processes: photoelectric effect, Compton effect, and pair
15. Photoelectric effect, or photoelectric absorption (PEA) is a form of
interaction of X-ray or gamma photon with the matter. A low energy
photon interacts with the electron in the atom and removes it from
its shell. The probability of this effect is maximum when the energy
of the incident photon is equal to or just greater than the binding
energy of the electron in its shell ('absorption edge') and the
electron is tightly bound (as in K shell). The electron that is removed
is then called a photoelectron. The incident photon is completely
absorbed in the process. Hence it forms one of the reasons for
attenuation of X-ray beam as it passes through the matter.
1- Photoelectric effect
16. 2- Compton scattering
Compton scattering takes place between the incident x-ray or
gamma-ray photons and an outer-shell electron. • The photon
transfers a portion of its energy to the electron, which is then
known as a recoil electron, or a Compton electron. • Photon is not
absorbed, but it loses energy and it changes direction (angle θ) •
almost independent of atomic number Z; • The Compton process
is most important for energy absorption for soft tissues in the
range from 100 keV to 10MeV
17. If a photon enters matter with an energy in excess of 1.022
MeV, it may interact by a process called pair production. •
The photon, passing near the nucleus of an atom and may
disappear as a photon and reappear as a positive and
negative electron pair. • The two electrons produced, e- and
e+ , are not scattered orbital electrons, but are created, in
the energy/mass conversion of the disappearing photon.
3- Pair Production
18. 1- …… occurs when a high-energy photon (> 1.02 MeV)
interacts with the nucleus of an atom.
2-……….occurs between tightly bound (inner-shell) electrons
and incident x-ray photons.
3- ……….incident photons interact with loosely bound
valence (outer-shell) electrons.
4- …………… It is produced when inner-shell electrons of the
anode target are ejected by the incident electrons.
5- ……………can be emitted from the nucleus of an atom
during radioactive decay
Question 1: Write the suitable expression for the following definition:
19. Question 2:Answer the following :
A) Radiation is classified into two main categories
B) What is the different between gamma ray and X- ray ?
22. Introduction to Radiation Oncology
Radiation has been an effective
tool for treating cancer for
more than 100 years.
About two-thirds of all cancer
patients will receive radiation
therapy as part of their
23. What is radiotherapy?
• Radiation therapy (also radiotherapy or radiation oncology)
• Radiation therapy is the medical use of ionizing radiation as part of
cancer treatment to control malignant cells
• Radiation therapy is an important part of cancer treatment in which
cancer patients are treated using high-energy radiation such as x-
rays, gamma rays, electrons, protons, and neutrons. Currently, about
half of all cancer patients receive radiation treatment during their
whole cancer care process.
• Radiotherapy is used for the treatment of malignant tumors
(cancer), and may be used as the primary therapy. It is also common
to combine radiotherapy with surgery, chemotherapy, hormone
therapy or some mixture of the three.
• Radiation therapy is a safe and effective treatment for many types
24. what is the aim of radiotherapy
• The aim of radiation therapy is to deliver a prescribed
dose of radiation to the tumor volume, while sparing
surrounding healthy tissues and organs.
• In other words, The goal of radiation therapy is to get
enough radiation into the body to kill the cancer cells
while preventing damage to healthy tissue. There are
several ways to do this. Depending on the location,
size and type of cancer, patient may receive one or a
combination of techniques.
• Treatment team will help the patient to decide which
treatments are best for him.
26. Meet the Radiation Oncology Team
This doctor specializes in
giving radiation therapy to
treat cancer. A radiation
oncologist oversees radiation
therapy treatments. He or
she works closely with other
team members to develop
the treatment plan.
27. Meet the Radiation Oncology Team
Medical Radiation Physicist
Medical physicists work directly with radiation
oncologist during treatment planning and delivery.
They are responsible for developing and directing
quality control programs for equipment and procedures.
They also make sure the equipment works properly by
taking precise measurements of the radiation beam and
performing other safety tests regularly.
Medical physicists also oversee the work of the
dosimetrist and help to ensure that complex treatments
are properly tailored for each patient.
28. Meet the Radiation Oncology Team
Works with the radiation
oncologist and medical
physicist to calculate the
proper dose of radiation
given to the tumor.
29. Meet the Radiation Oncology Team
• Radiation therapist or
• This professional operates
the treatment machines
and gives patients their
30. Meet the Radiation Oncology Team
Radiation Oncology Nurse
This nurse specializes in caring
for patients receiving radiation
therapy. A radiation oncology
nurse plays many roles,
• Answering questions about
• Monitoring patient's health
• Helping patient manage
potential side effects
32. Radiation therapy works by damaging the DNA within
cancer cells and destroying their ability to reproduce.
When the damaged cancer cells are destroyed by
radiation, the body naturally eliminates them.
Normal cells can be affected by radiation, but they are
able to repair themselves.
Sometimes radiation therapy is the only treatment a
Other times, it is combined with other treatments, like
surgery and chemotherapy.
33. IRRADIATION OF CELLS
When cells are exposed to ionizing radiation the standard
physical effects between radiation and the atoms or
molecules of the cells occur first and the possible biological
damage to cell functions follows later. The biological effects
of radiation result mainly from damage to the DNA, which is
the most critical target within the cell; however, there are also
other sites in the cell that, when damaged, may lead to cell
death. When directly ionizing radiation is absorbed
in biological material, the damage to the cell may occur in one
of two ways:
direct or indirect
34. Direct action in cell damage by radiation:
• The radiation interacts directly with the critical target in the
• The atoms of the target itself may be ionized or excited
through Coulomb interactions, leading to the chain of physical
and chemical events that eventually produce the biological
damage. Direct action is the dominant process in the
interaction of high LET (linear energy transfer) particles with
• linear energy transfer (LET) is the amount of energy that an
ionizing particle transfers to the material traversed per unit
distance. It describes the action of radiation into matter.
LET = dE/dl, where dE is the average energy locally imparted
to the medium by a charged particle of specified energy in
traversing a distance of dl.”
35. In direct action in cell damage by radiation:
• In indirect action the radiation interacts with other
molecules and atoms(mainly water, since about 80% of a
cell is composed of water) within the cell to produce free
radicals, which can, through diffusion in the cell, damage
the critical target within the cell.
• In interactions of radiation with water, short lived yet
extremely reactive free radicals such as H2O+ (water ion)
and OH•(hydroxyl radical) are produced.
• The free radicals in turn can cause damage to the target
within the cell.
• About two thirds of the biological damage by low LET
radiations(sparsely ionizing radiations) such as X rays or
electrons is due to indirect action.
36. The steps involved in producing biological damage by the
indirect action of X rays are as follows:
• Step 1: Primary photon interaction (photoelectric
effect, Compton effect and pair production) produces
a high energy electron.
• Step 2: The high energy electron in moving through
tissue produces free radicals in water.
• Step 3: The free radicals may produce changes in
DNA from breakage of chemical bonds.
• Step 4: The changes in chemical bonds result in
Step (1) is in the realm of physics; step (2) is in chemistry;
steps (3) and (4) are in radiobiology.
The amount of radiation used in
radiation therapy is measured in gray (Gy),
and varies depending on the type and
stage of cancer being treated. For curative
cases, the typical dose for a solid epithelial
tumor ranges from 60 to 80 Gy, while
lymphoma tumors are treated with 20 to
Radiotherapy fractions. The full dose of radiation is usually
divided into a number of smaller doses called fractions. This allows
healthy cells to recover between treatments.
Patient have the fractions as a series of treatment sessions that
make up his radiotherapy course.
40. 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- Internal radiation therapy
2- Eternal radiation therapy
41. 1- The full dose of radiation is usually divided into a number of smaller doses
2-When directly ionizing radiation is absorbed
in biological material, the damage to the cell may occur in one of two ways ………. Or
3- …………..is the doctor who oversees the radiation therapy treatments.
4- …………They are responsible for developing and directing quality control programs
for equipment and procedures.
5- ……………works by damaging the DNA within cancer cells and destroying their
ability to reproduce.
6- ……………. This professional operates the treatment machines and gives patients
their scheduled treatments.
Question 1: Write the suitable expression for the following definition:
42. Question 2:Answer the following :
A) The steps involved in producing biological damage by the indirect
action of X rays are as follows:
B) Explain the radiotherapy?
C)What is the meaning of radiotherapy dose?
C) What is the meaning of a word (LET) ?
D) what is the aim of radiotherapy?