This document discusses radiotherapy as a method for treating cancer. It describes how radiotherapy works by damaging the DNA of cancer cells, making them unable to reproduce. Two main techniques are discussed: external beam radiotherapy which uses x-rays or gamma rays to destroy tumors from outside the body, and brachytherapy which involves placing radioactive sources inside or near the tumor. The factors considered when determining appropriate treatment are also summarized.

1. Medical Equipment III
Radiotherapy
Inas A. Yassine
Systems and Biomedical Engineering Department,
Faculty of Engineering - Cairo University
iyassine@eng.cu.edu.eg

2. What is Cancer?
Cancers are growths of cells (cancerous tumours)
which are out of control. As a result of this, they do
not perform their intended function.

3. Normal and Cancer Cells

4. Treatment of Cancer
Cancerous tumors can be treated using the
following main methods:
¨ Chemotherapy (drugs).
¨ Radiation therapy (radiotherapy and
brachytherapy).
¨ Surgery (Best Option) taking the whole
thing off.

5. Objective of Radiotherapy
Radiotherapy may be used:
§ to cure an illness - for example, by
destroying a tumor (abnormal tissue)
§ to control symptoms - for example, to
relieve pain
§ before surgery - to shrink a tumor to make
it easier to remove
§ after surgery - to destroy small amounts of
tumor that may be left

6. What is Radiotherapy
§ damaging the DNA inside cells making them unable to divide and reproduce.
§ Abnormal cancer cells
§ Are more sensitive to radiation
§ divide more quickly than normal cells.
§ die and the tumor shrinks by the time
§ Normal cells
§ can also be damaged by radiation
§ repair themselves more effectively, as when your skin heals itself after sunburn
§ The goal of radiation therapy
§ maximize the dose to abnormal cells
§ minimize exposure to normal cells.
§ The effects of radiation are not immediate; the treatment benefit occurs over
time.

7. Choice of Treatment
The choice of treatment depends on a
number of factors including
§ Size of tumor.
§ Position of tumor.
§ Tumor Stage.
:

8. Radiation Therapy
§ There are two techniques in radiation therapy
that are used to treat cancer using ionizing
radiation:
§ Radiotherapy
§ Brachytherapy

9. External Beam Irradiation
§ Dual-energy linear accelerators generate:
§ Low energy megavoltage x-rays (4-6 MeV)
§ High energy x-rays (15-20 MeV)
§ Photon energy
§ Particle Radiation (electrons, protons,
neutrons)
§ Photon therapy advantages
§ Skin sparing, penetration, beam uniformity
§ Head and Neck sites – 4-6 MeV x-ray or Co60
gamma ray radiation

10. Radiotherapy Using X-rays
§ The x-rays are generated
by a linear accelerator
(linac).
§ The linac fires high energy
electrons at a metal target
and when the electrons
strike the target, x-rays
are produced.
§ The x-rays produced are
shaped into a narrow
beam by movable metal
shutters.

11. Radiotherapy Using Gamma Rays
§ Gamma rays are
emitted from a cobalt-
60 source – a
radioactive form of
cobalt.
§ The cobalt source is
kept within a thick,
heavy metal container.
§ This container has a slit
in it to allow a narrow
beam of gamma rays to
emerge.

12. Treatment of Cancer-Radiotherapy
§ The apparatus is arranged so that it can
rotate around the couch on which the
patient lies.
§ This allows the patient to receive
radiation from different directions.
§ The diseased tissue receives radiation all
of the time but the healthy tissue
receives the minimum amount of
radiation possible.
§ Treatments are given as a series of small
doses because cancerous cells are killed
more easily when they are dividing, and
not all cells divide at the same time – this
reduces some of the side effects which
come with radiotherapy.

13. Radiation Therapy- Brachytherapy
§ This involves placing implants
in the form of seeds, wires or
pellets directly into the tumor.
§ Such implants may be
temporary or permanent
depending on the implant and
the tumor itself.
§ The benefit of such a method
is that the tumor receives
nearly all of the dose whilst
healthy tissue hardly receives
any.

14. Brachytherapy
§ Uterus
§ Cervix
§ Prostate
§ Intraocular
§ Skin
§ Thyroid
§ Bone
Brachytherapy is used to treat the following cancers:

15. External Beam Irradiation

16. Brachytherapy
§ Radioactive source in direct contact with tumor
§ radioactive sources that are put inside the patient
§ The radioactive sources are sealed in needles, seeds,
wires, or catheters, and implanted directly into or near a
tumor on a temporary, Interstitial implants, intracavitary
implants or surface molds
§ Greater deliverable dose
§ Continuous low dose rate
§ Advantage for hypoxic or slow proliferators
§ Shorter treatment times

17. Brachytherapy
§ Limitations
§ Tumor must be accessible
§ Well-demarcated
§ Cannot be only modality for tumors with high
risk of regional lymph node metastasis

18. Brachytherapy

19. Radiobiology
§ Ionizing radiation ejects an electron from a
target molecule
§ Distributed randomly within cell
§ Double-strand DNA breaks – lethal
§ Cell death: no longer able to undergo
unlimited cell division
§ Direct vs. Indirect injury (free radicals – O2)
§ Inadequate cellular repair mechanisms implied

20. Radiobiology

21. Radiobiology
§ Random cell death
§ Deposition of energy & injury is random event
§ Same proportion of cells is damaged per dose
§ 100 to 10 cell reduction = 106 to 105 cell reduction
§ Larger tumors require more radiation
§ 105 cells = nonpalpable
§ Applies to normal tissue also
§ Therapeutic advantage – 4 R’s of radiobiology

22. Radiobiology
§ Use of high-energy radiation to treat cancer
§ destroys the cancer cells' ability to reproduce, and the
body naturally gets rid of these cells.
§ Radiation destroys cancer cells by damaging their DNA.
§ Cancer cells are particularly vulnerable to radiation
§ Cancer cells divide more rapidly than normal cells.
§ Normal cells are able to repair this damage more
efficiently.

23. Cancer Treatment and Radiotherapy
§ Cancer Treatment
§ Radiotherapy
§ Surgery
§ Chemotherapy
§ Radiotherapy
§ High energy x-ray that are highly penetrable
§ LINAC
§ Magnetron
§ Cyclotron
§ Cobalt

24. Diagnostic and Therapeutic X-Ray
§ Diagnostic radiology
§ uses low energy X rays for imaging
§ Radiotherapy
§ uses high energy X rays to treat tumor.
§ ionizes the water in the cell and induces formation of free
radicals which can damage of genetic material (DNA).
§ damage may be lethal and can cause death of the tumor cell.
However, often the damage is not enough to cause cell death
i.e. it is sublethal.
§ may be converted to lethal damage by repeated exposure to
radiation.
§ Normal cells are also affected adversely by radiation but have
the capacity of repair. reversible.

25. Measurement of radiation
Absorbed dose
§ Gy = 100 cGy (100 rad)
§ What is “rem”

26. High energy X-ray

27. Beam Collimation

28. LINAC and X-ray Machines
§ Both:
§ Provide a source of electrons in an evacuated tube
§ Require accelerating voltage between the anode and cathode
– Sd ada
§ sdasad
§ Dsadsa
X-RAY LINAC
30 to 150KV 4 to 35 MV
single(0.1 to 10 sec) shot
signal
several busts of 1/156sec
repeated hundred times a
second
Have collimators Thicker collimators
Shielded Heavily shielded
information about tissue
absorption that has been
transferred to the film
The importance is about the
energy absorbed by the tumor