1.
Types of Radiations
X-rays• α-particles• neutrons•
γ-rays• β-particles•
β+-particles•
Protons•
Carry enough energy which if deposited
in matter can produce ions

2.
Radiation therapy idea
Selective cell destruction (cancer)
How it can be done?
By destroying the cell using Energy
High energy particles damage a cell by altering it’s atom
Cause the atom’s electron to become excited and then ionized
Enzymes repair this damage
• But cancer cell slower than healthy cell
So, the end results (during radiation exposure )
More cancer cell end up dying more than healthy cell

3.
Reminder
• Absorbed dose D is the energy (joules) deposited per
unit mass (kg) of target material, D = dE/dm.
• The special unit of absorbed dose D is the Gray (Gy)
≡ 1 Joule/kg
• In biological systems
• Radiation Biologic effects dependent on “the
spatial distribution of energy deposition” (LET)
Linear Energy Transfer is energy deposited per unit path
length = dE/dx with units ev/cm

4.
Overview of presentation
• Photon therapy (briefly)
• Proton therapy (in detailed)
• How it works ?
• The remarkable phenomenon of physics “Bragg peak”
• Delivery of the beam (how it can be useful )
• How it can be produced ? (synchrotron)
• RBE of protons .
• Proton therapy Vs Photon therapy .(summary)

5.
The desirable goal
In order to treat cancer :
The main goal is to delivers a defined dose distribution
within the target volume and none out side it.
Now
Let’s see what type of radiation
would be the
Best??

6.
Treatment options
1) Photon therapy.
2) Proton therapy.

7.
Interactions of Photons
There are 3 modes:
• Photo-electric effect.
Entire energy transfer from
photon to an atomic electron .
• Compton effect.
Fraction of energy transferred to
Compton electrons.
• Pair production.

8.
What happen when a beam
of photon entering
a tissue ?

9.
Exponential behaviour
• It falls exponentially
E  E o exp( en x)
• Number of photon gets
attenuated
as depth increases .
• As their number decreases,
the dose that they deposit
decreases also
(proportionately ).

10.
Photon’s therapy failure
• Based on “how radiation
interacts with matter”
The failure is :
Most of the radiation is
deposited on healthy tissue.
Cause of failure !!
• They are not easy to control
Why ?
(low mass & high energy)
“Low LET”

11.
Treatment options
1) Photon therapy
2) Proton therapy.

12.
Did Proton therapy has the solution ?
What can Proton therapy provide ?

13.
Short story
• “A man with a vision “
In 1946 Harvard physicist ,
Robert Wilson suggested:
• Protons can be used clinically .
• Maximum radiation dose can
be placed into the tumor .
• Proton therapy provides
sparing of healthy tissues .

14.
Characteristics of protons
• Subatomic particle .
• Stable , positively charged .
• Heavy particle with mass 1800
that of electron.
• Very little scattered as they
travel through tissue .
• Travel in straight lines.
Which leads to very
Mp=1.672621636(83)×10−27 kg
Me= 9.10938215(45)×10−31 kg different modes of interactions
with matter .
Let’s see!!!!!!

15.
Interactions of Protons
• Coulomb interactions with
atomic electrons .
Electronic (ionization ,excitation)
• Coulomb interactions with
atomic nuclei .
“multiple Coulomb scattering.”
• Nuclear interactions with
atomic nuclei .
 Elastic nuclear collision
 Non elastic nuclear collision

16.
Key fact
Different modes of interactions
Means
Different dose distributions

17.
The shape of dose distribution
It means that :
• Low entrance dose
(plateau)
• Maximum dose at depth
(Bragg peak)
• Rapid distal dose fall-off
But
Why this shape of
distribution ?
Let’s see

18.
Remarkable phenomena
“Bragg peak”
Protons have the ability of
loosing little energy when
entering tissue .
But depositing more and
more as they slow
down…..
Finally, depositing a heavy
dose of radiation just
before they stop ,
giving rise to the
so-called Bragg peak

19.
Energy loss “dE/dx profiles
• a proton’s linear rate of
energy loss “linear energy
transfer” (LET)
• is given by the Bethe-
Block formula:

20.
Bragg Peak like (skiing)

21.
Bragg peak dependence on
energy
• The range is( the depth
of penetration
from the front surface to the
distal point on the Bragg
peak)
• Bragg peak
depends on the initial
energy of the protons so
the greater the energy, the
greater the range

22.
There is a problem
Is the current shape of
Bragg peak could provide
the tumor with uniform
dose ?
No, it can’t.
Because
The Bragg peak is too narrow
to fit the shape & depth of
the tumor

23.
Is there a solution ?
So, how to make the beam of proton useful for
treatment?
Is it possible to shape the beam to fit the
shape of the tumor ?
Let’s see!!!!!

24.
Smart Idea
• The spread-out Bragg peak
(SOBP):
• Extending the dose in depth
means
An extension in depth can be
Superposition of Bragg-peaks by
achieved by proton beams energy variation
of successively
delivering not just one, but
many Bragg peaks each
with different range (energy)
energy variation

25.
Beam delivery system Nozzle
There are two main approaches
( techniques) for shaping the
beam : (both laterally and in
depth)
1) passive scattering.
2)Scanned beam.

26.
passive scattering.

27.
Shaping the beam Laterally
The beam is spread
laterally to clinically
useful size by
double – scatterer
and compensator

28.
Tailoring the beam in depth:
the range modulator (fan like
The modulator spins
around in front of the
proton beam pulling the
beam back and forward
causing a flat topped
dose distribution
providing the tumor with a
uniform dose.

29.
Scanned beam
• Expand the lateral
dimensions of a proton
beam by using the
electromagnetic
technique to scan the beam
laterally & in shape .

30.
Synchrotrons The engine)
• What is Synchrotron
mission ?
• They produce the proton
beam .
• It is a modified Cyclotrons.
synchrotron provides energy
variation by extracting the
protons when they have
reached the desired
energy.

31.
Hardware components
• Proton accelerator
• Beam transport
system
• Treatment Rooms
• Gantry
• Standard table

32.
A word about Treatment plane
How do you know what
to include and what to
exclude in treating
deep –seated tumors
with radiation?
By using number of
imaging tools
(CT,MRI,PET….)
Gives ability to see
To image
To map

33.
Relative Biological Effectiveness
of proton
RBE is the ratio of the dose of reference radiation beam
(e.g., photons) to that of test beam (e.g., protons)
required to produce a defined biological response .
• Is used to compare the biologic effects of various
radiation sources .
Protons has exactly the same biologic effects as X-rays!!
Because the calculated RBE is 1.1
The bottom line is that the only difference between
protons and standard X-rays lies in the physical
properties of the beam and not in the biologic effects
in tissue.

34.
SUMMARY
• Photon therapy Proton therapy
the interactions are stochastic . they are deterministic events .
they not easy to control . They easier to control .
At point of entrance,
It receive large amount of dose. It receive very small dose .
As they reached the tumor,
Continue to pass through tissue a sharp burst of energy released
at tumor and none beyond it.
Used for treat superficial tumors. ideal for tumors in or near
critical structures (brain, heart,
eye) pediatric cancers.

35.
References and sites
• Radiation Oncology A Physicist's-Eye View: Michael
Goitein .
• Radiation therapy physics: William R Hendee &
Geoffrey .
• Sites:
• www.wikipedia.org
• Loma Linda University Medical Center
www.llu.edu
• www.mpri.org
• www.proton-therapy.org
• http://www.varian.com/