Proton therapy uses protons to treat cancer. Protons deposit most of their energy at a specific depth, called the Bragg peak. This allows doctors to precisely target the tumor while minimizing radiation exposure to surrounding healthy tissue. Proton therapy is used to treat many types of cancers in the brain, head and neck region, lung, prostate, and other areas. It provides dosimetric advantages over photon therapy by reducing radiation doses to nearby critical structures like optic nerves and the spinal cord.

2. WHAT IS PROTON ?
 The existence of proton was first
demonstrated by Ernest Rutherford in 1919.
 Proton is the nucleus of hydrogen atom
 It has a positive charge of 1.6 x 10^ 19 c
 Mass is 1.6 x 10 ^ -27 kg
 Most stable particle in universe , halflife
more than 10^32 years.

3. What is proton ? Cont....
 A proton is a subatomic particle, symbol p or p+
with a positive electric charge and mass slightly less
than that of a neutron
 Protons are spin-½ fermions and are composed of
three valence quarks, making them baryons (a sub-
type of hadrons). The two up quarks and one down
quark of a proton are held together by the strong force,
mediated by gluons

4. MECHANISM OF PROTON THERAPY
 Protons are a superior form of radiation therapy.
 Fundamentally, all tissues are made up of
molecules with atoms as their building blocks. In
the center of every atom is the nucleus. Orbiting
the nucleus of the atom are negatively charged
electrons

5.  When energized charged particles, such as
protons pass near orbiting electrons, the positive
charge of the protons attracts the negatively
charged electrons, pulling them out of their orbits.
This is called ionization.
 Because of ionization, the radiation damages
molecules within the cells, especially the DNA or
genetic material. Damaging the DNA destroys
specific cell functions, particularly the ability to
divide or proliferate.

6.  The major advantage of proton treatment over
conventional radiation, however, is that the energy
distribution of protons can be directed and
deposited in tissue volumes designated by the
physicians-in a three-dimensional pattern from
each beam used.
 Protons are energized to specific velocities. These
energies determine how deeply in the body
protons will deposit their maximum energy. As the
protons move through the body, they slow down,
causing increased interaction with orbiting
electrons

7.  Maximum interaction with electrons occurs as the
protons approach their targeted stopping point.
Thus, maximum energy is released within the
designated cancer volume. The surrounding
healthy cells receive significantly less injury than
the cells in the designated volume.
 Overall effect of proton was fewer harmful side
effects, more direct impact on the tumor, and
increased tumor control."

10. HOW PROTONS ARE PRODUCED
 Protons are produced from
1. Cyclotrons
2. Synchrotrons
CYCLOTRON
 Cyclotron - a short metallic cylinder divided into two
sections, usually referred to as dees
 Dees are highly evacuated and subjected to a constant
strength magnetic field applied perpendicular to the
plane of the dees. A square wave of electric field is
applied across the gap between the two dees.

11.  Protons are injected at the center of the cyclotron and
accelerated each time they cross the gap.
 The polarity of the electric field is switched at the
exact time the beam re-enters the gap fromthe
opposite direction. The constant magnetic field
confines the beam in ever-increasing orbits within the
dees until the maximum energy is achieved and
extracted

12. SYNCHROTRON
 In the synchrotron, a proton beam of 3 to 7 MeV,
typically from a linear accelerator, is injected and
circulated in a narrow vacuum tube ring by the
action of magnets located along the circular path
of the beam.
 The proton beam is accelerated repeatedly through
the Radiofrequency cavity powered by a
sinusoidal voltage with a frequency that matches
the frequency of the circulating protons.

13.  Protons are kept within the tube ring by the
bending action of the magnets.
 The strength of the magnetic field and the RF
frequency are increased in synchrony with the
increase in beam energy, hence the name
synchrotron.
 When thebeam reaches the desired energy, it is
extracted

15. Beam Delivery Systems
 A single accelerator can provide proton beam in
several treatment rooms. Beam transport to a
particular room is controlled by bending
magnets, which can be selectively energized to
switch the beam to the desired room.
 An electronic safety system is provided to
ensure that the beam is switched to only one
room at a time and only when the designated
room is ready to receive the beam. There is very
little loss of beam intensity in the transport
system—usually less than 5%.

16.  The particle beam diameter is as small as
possible during transport. Just before the
patient enters the treatment room, the
beam is spread out to its required field
cross section in the treatment head—the
nozzle.

17.  This beam spreading is done in two ways:
(a) passive scattering,
in which the beam is scattered using thin
sheets of high-atomic-number materials
(e.g., lead, to provide maximum scattering
and minimum energy loss)
(b) scanning, in which
magnets are used to scan the beam over
the volume to be treated. Although most
accelerators currently use passive systems,
there is a trend toward scanning to spread
the beam.

18. Why linear accelaerators not used?
 Conventional linear accelerators are not suitable
for accelerating protons or heavier charged
particles to high energies required for
radiotherapy
 The electric field strength in the accelerator
structure is not sufficient to build a compact
machine for proton beam therapy
 A linear accelerator would require a large amount
of space to generate proton beams in the
clinically useful range of energies.

19. PHYSICS BEHIND THERAPY
BRAGG PEAK
 The average rate of energy loss of a particle per
unit path length in a medium is called the
stopping power. The linear stopping power (–
dE/dx) is measured in units of MeV/cm.
 Stopping power and LET, are closely related to
dose deposition in a medium and with the
biologic effectiveness of radiation.

20.  The rate of energy loss due to ionization and
excitation caused by a charged particle traveling
in a medium is proportional to the square of the
particle charge and inversely proportional to the
square of its velocity.
 As the particle loses energy, it slows down and
the rate of energy loss per unit path length
increases. As the particle velocity approaches
zero near the end of its range, the rate of energy
loss becomes maximum

21. Proton beam, there is a slow increase in dose with
depth initially, followed by a sharp increase near the
end of range. This sharp increase or peak in dose
deposition at the end of particle range is called the
Bragg peak

22. Spread out bragg peak
 To provide wider depth coverage, the Braggpeak
can be spread out by superposition of several
beams of different energies . These beams are
called the spread-out Bragg peak (SOBP)
beams.
 The SOBP beams are generated by employing a
monoenergetic beam of sufficiently high energy
and range to cover the distal end of the target
volume and adding beams of decreasing energy
and intensity to cover the proximal portion.

24. Clinical applications
 LUNG CANCER
In proton therapy small volume volume of non
targeted lung tissue, spinal cord, esophagus, and
heart is exposed to radiation
3 D CRT IMRT PROTON
LUNG DOSE 23 % 19 % 1 1 %
HEART
DOSE
15 % 9 % 7 %
ESOPHAGUS
DOSE
45 % 35 % 28.7 %

25. Pancreatic Cancers
 Pancreatic cancers have an extremely low therapeutic ratio with
radiation alone or combined with surgery and chemotherapy.
 The disease is frequently localized for a window of time before
spreading, providing a potential opportunity to improve the
overall outcome by intensifying local therapy.
 Doses will be limited by OAR are kidneys, bowel, liver.
IMRT PROTON
LIVER 23 % 15 %
SMALL BOWEL 34 % 9 %

26.  Savings in normal-tissue exposure may be
leveraged to permit either radiation or
chemotherapy dose escalation or intensification,
potentially increasing the opportunity for
complete surgical resection, cure, or both in
pancreatic cancer
Prostate Cancer
 Prostate cancer results with IMRT are generally
excellent, but dose-escalation trials from the
M.D. Anderson show that the volumes of rectum
and rectal wall receiving low- to moderate-dose
radiation with x-ray based therapy are
significantly associated with the incidence of

27. Rectal wall V30, V40, and V50 were 29%, 23%,
and 17% with IMRT compared with 18%, 16%, and
14% with proton therapy, respectively, potentially
providing a lower risk of rectal injury .
Paranasal Sinus Tumors
 Paranasal sinus tumors frequently extend into
the orbit or anterior cranial fossa adjacent to
critical optic structures, such as the chiasm, optic
nerves, retinae, lacrimal glands, cornea, and
lens

28.  There is relative sparing of most of the optic structures
with proton therapy with mean doses to the chiasm, right
optic nerve, left optic nerve, and brainstem of 44and 36
Gy (RBE), 53 and 43 Gy (RBE), 44 and 36 Gy (RBE),
and 43 and 29 Gy (RBE) with the IMRT and proton plans,
respectively
Skull-Base Sarcomas
 Skull-base sarcomas frequently are not amenable to
complete resection and require very high radiation doses
for disease control.
 The significant reduction in relative dose to the brainstem
and spinal cord permits the delivery of higher doses to
the tumor with proton therapy

29. Craniospinal Axis Irradiation
Craniospinal axis irradiation is required in most
 medulloblastoma
 metastatic germ cell tumors
 primitive neuroectodermal tumors (PNETs)
 ependymomas.
 Most patientswith these tumors are young and at risk for
late effects of radiation. the exit dose from photon
therapy exposes the thyroid, heart, lung, gut, and gonads
to functional and neoplastic risks that can be avoided
with proton therapy.
 The total-body V10 and total-body integral dose are,
respectively, 37.2% and 0.223 Gy-m3 with 3DCRT
compared with 28.7% and 0.185 Gy-m3 with proton
therapy, a reduction likely to result in a lower risk of
second malignancy.

30. Lymphomas
 Lymphomas frequently involve the mediastinum
but typically require only a moderate dose of
radiation therapy in conjunction with
chemotherapy for disease control.
 Unfortunately, even low to moderate radiation
doses place the patient at risk
for late cardiac injury and second cancers,
particularly breast cancers.
 The proton therapy shows a significant reduction
in the volume of heart, lung, breast, spinal cord,
and other soft tissues exposed to low-dose
irradiation

31. Craniopharyngioma
 Craniopharyngioma is usually diagnosed in children
and adolescents.
 Its suprasellar location places the temporal lobes,
hippocampi, hypothalamus, optic chiasm, and
nerves at risk for radiation injury.
 The relative mean doses with IMRT, SRT, and proton
therapy for the following structures
 are right temporal lobe—17%, 20%, and 8%;
 left temporal lobe—18%, 22%, and 10%;
 left hippocampus—50%, 61%, and 16%;
 right cochlea—16%, 7%, and 0%; and
 left cochlea—14%,16%, and 1%, respectively.
 These reductions in dose to nontargeted brain
tissues with proton therapy are likely to result in
reduced loss in neurocognitive and auditory function

32.  IMRT  PROTON

33. PROTON THERAPY USED IN
 Base of skull sarcomas
 Brain and spinal cord tumors
 Paranasal sinus tumors
 Oropharyngeal carcinoma
 Esophageal cancer
 Early- and advanced-stage lung cancer
 Eye cancers

34.  Low-, intermediate-, and highrisk prostate
cancer
 Hodgkin and other lymphomas
 Sarcomas
 Pediatric malignancies
 Hepatocellular carcinoma
 Pancreatic cancer
 Cervical cancer and

35. BENIGN LESIONS
 Acoustic neuroma,
 Vestibular schwannoma,
 Arteriovenous malformations (AVMs),
 Age-related macular degeneration,
 Pituitary adenomas,
 Skull based chordomas
 Craniopharyngiomas, and
 Meningioma

36. CONCLUSION
 Proton therapy offers the promise of reduced
toxicity to patients compared with photon therapy
by reducing the radiation dose to nontargeted
tissues.
 Reduced toxicity may be leveraged to increase
disease control through dose escalation or
intensification (hypofractionation).
 Problem lies on it cost factor and availability