Proton beam therapy

Proton Beam Therapy

1. Proton Beam Therapy
Prof Amin E A Amin
Dean of the Higher Institute of Optics Technology
&
Prof of Medical Physics
Radiation Oncology Department
Faculty of Medicine
Ain Shams University

2. Proton Beam Therapy

3. Introduction
➢Protontherapy(also called proton beam therapy)is a
form of external beam radiotherapy using beams of
energeticprotonsrather than x-raysfor cancer treatment.
➢Proton therapy is one type particle therapy which is
sometimes referred to, more correctly, as hadron therapy
(that is, therapy with particles that are made of quarks).
➢Protons produced by cyclotrons and synchrotrons
➢At high energy, protons can destroy cancercells.

4. History of Proton Beam Therapy
❖1919: Proton was first
discovered by Ernest Rutherford
in1919.
❖1946: The first suggestion that
energetic protons could be an
effective treatment method was
made by Robert R. Wilson in a
paper published in 1946 while he
was involved in the design of the
Harvard Cyclotron Laboratory
(HCL).
Ernest
Rutherford
Robert R.
Wilson

5. History of Proton Beam Therapy
❖1954: The first treatments were performed with particle
acceleratorsbuilt for physics research, notably Berkeley
Radiation Laboratory in 1954 and at Uppsalain Sweden in 1957.
❖1957: Uppsala in Sweden duplicates Berkeley results onpatients.
❖1961: In 1961, a collaboration began between HCL and the
Massachusetts General Hospital(MGH) to pursue proton therapy.
Over the next 41 years, this program refined and expanded these
techniques while treating 9,116 patientsbefore the cyclotron was
shut down in 2002.

6. History of Proton Beam Therapy
❖1989: The world's first hospital-based proton therapy center was a
low energy cyclotron centrefor ocular tumors at the Clatterbridge
Centre for Oncology in the UK, opened in 1989,followed in 1990
at the Loma Linda University Medical Center (LLUMC)
inLoma Linda, California.
❖2001: Later, the Northeast Proton Therapy Center at
Massachusetts General Hospital was brought online, and the HCL
treatment program was transferred to it during 2001 and 2002.
❖2010: By 2010 these facilities were joined by an additional seven
regional hospital-based proton therapy centers in the United
States alone, and many more worldwide.

7. HISTORY
•In 1946 Harvard physicist Robert Wilson
(1914-2000) suggested*:
•Protons can be used clinically
•Accelerators areavailable
•Maximum radiation dose can be placed into thetumor
•Proton therapy provides sparing of normal
tissues
•Modulator wheelscanspread narrow Braggpeak

8. Rationale Of Proton Therapy
➢To Reduce dose to non targetregions
➢Doseescalation
➢To Reduce probable secondmalignancies
➢Better constraints to Organ atRisk

9. Characteristics ofProtons
➢The Existence of proton was first demonstrated by Ernest
Rutherford in1919
➢It is Subatomic particle
➢Proton is thenucleusofhydrogenatom
➢It has a positive charge of 1.6 x 10
19
C
➢Its mass is 1.6x10
-27
kg(1840 times of electron)
➢It consists of 3 Quarks(two up andone down)
➢It is the most stable particle inuniverse with halflifeof
>10
32
years

10. Characteristics ofProtons
•Very little scattered as they travel through tissue.
•Travel in straightlines.
•Which leads to very different modes ofinteractionswith
matter.

11. ProtonInteractions
➢Itinteractswithelectrons and
atomic nuclei inthe medium
through coulombforce.
➢The interaction could be;
a.Inelasticcollisions
b.Elasticscattering
➢Protonsscatterthroughsmaller
anglessotheyhave sharper lateral
distribution thanphotons.
.

12. Interactions Of A Proton In Matter
Interactions of a
proton in matter
interactionsswith
electrons
Ionization
Excitation
interactionswith
nuclei
Elastic coulomb
scattering with
nucleus
Non-elastic
nuclear
interaction

13. Coulomb InteractionsWith Atomic
Electrons
These interactions are either ionizationor excitation.

14. Excitation andIonization
p
e
pp p
e
E
transfer <E
binding
Electron excited to ahigher
energy level in theatom
E
transfer >=E
binding
Electron escapes fromthe
atom
➢Mean energy transfer to electron very low (m
p >> m
e) Mean
energy transfer does notdepend on protonenergy
➢Interaction probability is inversely proportionalto proton energy

15. Coulomb InteractionsWith Atomic
Electrons
Inelastic Coulomb interaction with
atomic electrons: it is a dominating
interaction:
•Ionization (=dose)
•Small energy loss per interaction 
Continuous slowing down of proton Well-
defined range
•Range secondary electrons < 1mm Dose
is absorbed locally
•No significant deflection of protons (m
p=
1832m
e)
.

16. Nuclear Interactions Of Protons
•A certain fraction of protons undergo nuclear interactions.
•Nuclear interactions lead to secondary particles and thus to
local and non-local dose deposition, including neutron.
γ
n
p’
p
p
p’

17. Nuclear Interactions Of Protons
•Coulomb interactionswith
atomic nuclei.
•“multiple Coulomb scattering.”
•Nuclear interactionswith
atomic nuclei.
▪Elastic nuclearcollision
▪Nonelasticnuclearcollision

18. Elastic Coulomb Scattering With Nucleus
•Lateral scattering of
treatment field versus
depth

19. Non-Elastic Nuclear Interaction
•Neutrons are the main
external radiation
hazard

20. ➢It is higherwith low atomic numbermaterials and low with
high atomic number materials
➢High Z materials=Scattering
➢Low Z materials= Absorption of energyand slowing down
Protons
Mass StoppingPower

21. Linear EnergyTransfer
➢It is defined as the average energydeposited per unit length of
trackof radiation and it’sunit iskeV/μm.
➢Therateofenergylossduetoionisationandexcitation
caused by a charged particle travelling in a medium is
proportional to the square of the particle charge and inversely
proportionaltothesquareofitsvelocity.
➢Astheparticlevelocityapproacheszeroneartheendofits
range, the rate of energy loss becomesmaximum.
➢Thesharpincreaseorpeakindosedepositionattheendof
particle range is called the Braggpeak.

22. Linear EnergyTransfer
•Charged particles generally have higher
LET than X and γ rays because of their
greater energy deposition along the
track.
•biological effect of a radiation (its
relative biological effectiveness, RBE)
depends onits averageLET.

23. •a proton’s linear rate of
energy loss “linear
energy transfer”(LET)
is given by theBethe-
Blockformula:
Energy Loss (LET Profile)

24. RBE
•Besides this very precise energy loss, the relative biological
effectfor protons is far more important than for photons.
•Protons are much more ionizing than x-or gamma ray
photons.

25. RBE
Relative Biological
Effectiveness (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.
RBE OF PROTONS IS1.1

26. RBE
➢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 is1.1
➢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 intissue.

27. RBE
➢Inclinicalpractice,RBEof1.1 isgenerallyused
(Sameasphotonsbutwithbetterphysical
properties)
➢However,RBEchangesasthereischangeinLET
(LETincreaseswhenenergydecreases towards
the end of therange)
➢ThereisrapidriseinRBEduringlastseveralmm3
oftheprotonrangeproducing an RBE value of1.3.
➢ActualRBEcorrecteddosemayexceed
physicaldoseby25%attheendofthe
spectrum

28. Description
➢Proton therapy is a type of external beam radiotherapyusing
ionizing radiation.
➢During treatment, a particle accelerator is used totarget the
tumor with a beam of protons.
➢These charged particles damage the DNA of cell, ultimately
causing their death or interfering with their ability toproliferate.
➢Due to their relatively large mass, protons have little lateral side
scatter in the tissue; the beam does not broaden much, stays
focused on the tumor shape and delivers only low-dose side-
effects to surroundingtissue.

29. Description(Cont)
➢All protons of a given energy have a certainrange; very few
protons penetrate beyond that distance.
➢Furthermore, thedosedelivered to tissue is maximum just over
the last few millimeters of the particle’s range; this maximum is
called theBragg peak.
➢The accelerators used for proton therapy typically produce
protons with energies in the range of 70 to 250 MeV
➢By adjusting the energy of the protons during application of
treatment, the cell damage due to the proton beam is maximized
within the tumoritself.

30. Physical Basis OfParticle Therapy
➢Inprotontherapy,energeticprotonsaredirectedatthetarget
tumor.
➢Thedoseincreaseswhiletheparticlepenetratesthetissue,up
toamaximum(theBraggpeak)thatoccursneartheendof
theparticle'srange,anditthendropsto(almost)zero.
➢Theadvantageofthisenergydepositionprofileisthatless
energyisdepositedintothehealthytissuesurroundingthe
targettissue.

31. Photon Vs Proton
Radiation Effects
Photon Therapy
the interactions are stochastic.
They are not easy to control.
Proton Therapy
they are deterministic events .
They easier to control.

32. At point ofentrance
Photon Therapy
It receive large amount
ofdose.
Proton Therapy
It receive very small
dose.
Photon Vs Proton

33. As they reached thetumor
Photon Therapy
Continue to pass
throughtissue
Used for treat
superficialtumors.
Proton Therapy
a sharp burst of
energy released at
tumor and none
beyond it.
ideal for tumors in or
near critical structures
(brain, heart, eye)
pediatriccancers.
Photon Vs Proton

34. Photon Vs Proton
Photons: Protons:
15 MeV R = 20, M 10 cm

35. Photon Vs Proton
Photons: Protons:
15 MeV R = 20, M 10 cm

36. Photon Vs Proton
Photons: Protons:
15 MeV R = 20, M 10 cm

37. Lateral PenumbraComparison
Photon (6 MV) vs Proton (Range 14 / Mod 10cm)

38. Why ProtonsAre Advantageous
➢Relatively low entrance
dose (plateau)
➢Maximum dose at
depth (Braggpeak)
➢Rapid distal dosefall-off
➢Energy modulation
(Spread-out Bragg
peak)

39. TherapeuticRatio

40. Rationale
Relative dosedistribution

41. ❑Constant principle in radiation oncology is that higher or
more intensetheradiationdose,thegreatertheprobability
oftumour control
❑The primary barrier to maximising local tumour control
through dose escalation or intensification is the risk of
damaging normaltissueseitherbydeliveringtoohighdose
orexposingtoomuchof the normal tissue toradiation.
Rationale

42. ❑Inmostclinicalsettings,thereisanopportunityforimprovement
of therapeutic ratio by increasing disease control or by reducing
toxicity.
❑The most direct means of improving the therapeutic ratio is by
reducing dose to non-targeted tissues, which both reducestoxicity
andfacilitatesdoseescalationforincreasedtumourcontrol
Herein lies the rationale forproton therapy
Rationale

43. Limitations Of Conventional Photon
BasedTreatments
➢Significant exitdose
➢Dependent biological effect on oxygen
(indirect effect;70-80%)
➢Dose escalation not possible beyond alimit
➢Secondmalignancies

44. Problem With X-rays And The Promise
And Challenge OfProtons
•The shape of the depth-
dose curves for electrons,
photons (X-rays), a pristine
proton Bragg peak and a
spread-out Bragg peak,
composed of multiple
pristine Bragg peaks,
differs significantlt.

45. Problem With X-rays And The Promise
And Challenge OfProtons
•Compared to photons or electrons, the entrance dose with
protons is constant and reduced relative to the target dose and
there is no exit dose.
•The dose fall-off at the end of the proton range is much
sharper than for electrons.
•In summary, with photons, most of the radiation energy is
deposited outside of the target, whereas with protons, most of
the radiation energy is deposited inside the target.

46. Proton DoseDistribution
➢Low entrance dose(plateau)
➢Maximum dose atdepth
(Braggpeak)
➢Rapid distal dosefall-off
Photons Protons

47. BraggPeak
➢Protons have the ability
of loosing littleenergy
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 tothe
so-called Braggpeak

48. Bragg Peak DependenceOn Energy
➢The range is (the depth ofpenetration from the front surface to
the distal point on the Bragg peak).
➢Bragg peak depends on theinitial energy of the protons so
the greater the energy,the greater therange

49. RangeStraggling
Energy variation
increases with
depth of
penetration Low
energy beams have
narrower Bragg
peaks

50. 1.TheincreaseofdE/dxastheprotonslowsdowncausesthe
overallupwardssweep.
2.Thedepthofpenetration(measuredbyd
80)increaseswithbeam
energy.
3.Thewidthofthepeakisthequadraticsumofrangestraggling
andbeamenergyspread.
4.Theoverallshapedependsonthebeam’stransversesize.Usea
broadbeam.
5.Non-elasticnuclearreactionsmovedosefromthepeakupstream.
Anatomy Of The Bragg Peak

51. 6.Ashorteffectivesourcedistancereducesthepeak/entranceratio.
Besureyouknowandrecordyoursourcedistance.
7.Lowenergybeamcontamination(asfromcollimatorscatter)may
affecttheentranceregion.Useanopenbeam.
8.Theexactshapedependssomewhatonthedosimeterused.Usethe
samedosimeteryouplantouselaterinQA.
Anatomy Of The Bragg Peak

52. Bragg Peak
❖The depth at which the peak occurs can be controlled by the
amount of energy the protons are given by their accelerator.
❖The proton's dose of radiation is released in an exact shape
and depth within the body. Tissues in front of the target
receive a very small dose, while tissues adjacent to the tumor
receive virtually none.
❖Experimentally the range of a 125 MeV proton in tissue is 12
cm, while that of a 200 MeV proton is 27 cm.
❖It is clear that protons with enough energy can penetrate to
any part of the body.

53. ❖The proton proceeds through the tissue in very nearly a straight
line (very little scatter), and the tissue is ionized at the expense of
the energy of the proton until the proton is stopped.
❖The dosage is proportional to the ionization per centimeter of
path, or specific ionization, and this varies almost inversely with
the energy of the proton.
❖Thus the specific ionization or dose is many times less where the
proton enters the tissue at high energy than it is in the last
centimeter of the path where the proton is brought to rest.
Bragg Peak

54. ❖The Bragg peak for
electrons, protons and
photons.
❖By adjusting the energy
of the protons we can
control the depth at
which they deposit their
energy.
http://www.oncoprof.net/Generale2000/g08_Radiotherapie/Images/PicBragg.gif
Bragg Peak

55. Conventional Radiotherapy And
ProtonTherapy

56. Conventional Radiotherapy And
ProtonTherapy

57. Conventional Radiotherapy And
ProtonTherapy
ROI
Beam
intensity
Profile
PatientTumor
Beam
intensity
Profile
ROI
Tumour
Beam
intensity
Profile
Beam
intensity
Profile
Beam
intensity
Profile
Beam
intensity
Profile

58. ➢TheBraggpeakofa
monoenergeticprotonbeamis
toonarrowtocovertheextent
of most targetvolumes.
➢Inordertoprovidewiderdepth
coverage,theBraggpeakcanbe
spreadoutbysuperim-position
of several beams of different
energies.
➢Called as spread-out Bragg
peak(SOBP).
Problems with Braggpeak
SOBP

59. SpreadOut Bragg Peak(SOBP)
•In a typical treatment plan
for proton therapy, the
Spread OutBragg Peak
(SOBP, dashed blue line),
is the therapeutic radiation
distribution.
•The SOBP is the sum of
several individual Bragg
peaks (thin blue lines) at
staggereddepths.

60. SpreadOut Bragg Peak(SOBP)
•Thedepth-dose plot of an
x-ray beam (red line) is
provided for comparison.
•The pink area represents
the additional dose
delivered by x-ray
radiotherapy which can be
the source of damage to
normal tissues and of
secondary cancers,
especially of theskin.

61. SpreadOut Bragg Peak(SOBP)
Extendingthedoseindepthmeans:Anextensionindepthcan
beachievedbyprotonbeamsofsuccessivelydeliveringnotjust
one,butmanyBraggpeakseachwithdifferentrange(energy).

62. SOBP
SOBP
Active
modulation
Passive
modulati

63. SOBP
Activemodulation Passivemodulation
➢A tightly focused pencilbeam is
deflected by 2 magnetic dipoles to allow
scanning of the beam over t/t field
➢Energy of the incomingbeam is varied
duringt/t
➢Dose distribution canbe tailored to any
irregulartm
➢Treatment planningis complex
➢A safety margin isadded for the
movement
➢Increased nuclear fragments (including
neutrons) areproduced by nuclear
interactions with beammodifiers
➢A beam of particles of fixed energy is
attenuated by range shifters of variable
thickness
➢Collimators &compensators areused
➢Treatment planning issimple
➢Disadv.-significant dose is delivered
along theentrance path
➢Extremely sensitive to movements of
thetarget
➢Integral doseis minimized.

64. PassiveScattering

65. Shaping the beamLaterally
The beam is spread laterally toclinically useful sizeby
double –scattererandcompensator

66. Tailoring The Beam InDepth:
The Range Modulator (FanLike
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 u
niformedose.

67. ActiveModulation (ScannedBeam)
Expand the lateral dimensions
of a proton beam by using the
electromagnetic technique to
scan thebeam laterally & in
shape.

68. Unit Of DoseDelivered
➢DosedeliveredwithparticlesareprescribedinGray
equivalents(GyE)
➢CobaltGrayequivalents(CGE)oftenusedwithprotons
➢Theseunitsareequaltomeasuredphysicaldosein Gray
timesthespecificRBEofthebeamused
➢Forprotonsabsorbeddoseismultipliedby1.1to express
thebiologiceffectiveprotondose

69. Components Of Proton BeamTherapy
➢Protonaccelerator
➢Beamtransport system
➢Gantry
➢Treatmentdelivery system

70. Generation OfProton
➢Protonsareproducedfrom hydrogengas;
➢Eitherobtainedfromelectrolysisofdeionized water
or
➢commercially available high-purityhydrogen gas.
➢Applicationofahigh-voltageelectriccurrenttothe hydrogen
gas strips the electrons off the hydrogen atoms, leaving
positively chargedprotons.

71. ProtonAccelerators
➢LinearAccelerator
➢Cyclotron
➢Synchrotron
➢High gradient EletrostaticAccelerator
➢Laser Plasma particleAccelerator

72. ➢It is a fixed energy machine
which produces continuous
beamofmonoenergetic(250
MeV Range)protons.
➢Cyclotrons can produce a large
protonbeam current of up to
300 nA and thus deliver proton
therapy at a high doserate.
Cyclotron

73. Cyclotron
➢Two short metallic cylinders, called
Dees
➢Placed between poles of direct
magneticfield
➢An alternating potential is applied
betweenDees.
➢Frequencyisadjustedofalternating
potentialtoacceleratetheparticleas
itpasses from one Dee toanother.
➢Witheachpass,theenergyofthe
particleandtheradiusoftheorbit
increases.

74. ➢EnergyDegradators
Modify Range and intensity ofbeam
➢Energy selection system(ESS)
consist of energy slits, bending magnets, and focusing
magnets, is then used to eliminate protons with excessive
energy or deviations in angulardirection.
Cyclotron

75. Disadvantage OfCyclotron
➢Inabilitytochangetheenergyofextractedparticles
directly
➢Energy degradation by material in the beam pathleads to an
increase in energy spread and beam emittance and reduces
the efficiency of thesystem
➢More shielding is required because ofsecondary
radiation

76. ➢What isSynchrotron
mission?
➢They produce the proton beam.
➢It is a modifiedCyclotrons.
➢synchrotron providesenergy
variation by extractingthe protons
when theyhave reached the
desired energy.
Syncrotron

77. Syncrotron
➢Produce proton beams of selectable energy,
therebyeliminating the need for the energy
degrader and energy selectiondevices
➢Beam currents are typically much lower than
with cyclotrons, thus limiting the maximum
doserates that canbeusedforpatient
treatment,especiallyforlargerfieldsizes
➢Themaximumdoserateavailablefroma
commercially availablesynchrotronbased
protondeliverysystemfor 25×25 cm
2
field
has been specified at 0.8Gy perminute.

78. Syncrotron
➢Protonpulseexitingapre-
accelerator,withenergytypically
up to7MeVisinjected into ring
shapedaccelerator.
➢Eachcompletecircuitoftheproton
pulsethroughtheaccelerator
increasesthe protonenergy.
➢Whenthedesiredenergyis
reached,theprotonpulseis
extracted fromthe applicator.

79. Beam TransportSystem
➢The proton beam, whether exiting the ESSor asynchrotron-
basedsystemis transported to the treatment room(s) via the
beam transportsystem.
➢Maintenance of beam focusing, centering, spot size, and
divergence throughout the beam transport system is critical to
maintaining a high-quality proton beam for treatment delivery.
➢Consistsofbendingandfocusingmagnetsandbeamprofile
monitorsto check and modify beam quality as it is transported
through the beam transportsystem.

80. Beam Line/ TransportSystem
➢Gantriesare usually large because of 2 reasons.
❖Protonswiththerapeuticenergiescan onlybebentwithlargeradii
and
❖Beam monitoring and beam shaping devices have to be
positioned inside the treatment head affecting thesize of the
nozzle
➢Nozzlehasasnoutformounting and positioning of field
specific aperture andcompensator

81. Beam TransportSystem

82. Beam TransportSystem

83. Beam DeliverySystem
➢The proton beam exiting the transport system is a pencil-
shaped beam with minimal energy and directionspread.
➢The beam has a small spot size in its lateral direction and a
narrow Bragg peak dose in its depthdirection.
➢This dose distribution is not suitable for practical size of
tumors.

84. Beam DeliverySystem
Pencil beam is modified eitherby
1.Scattering BeamTechnique
2.Scanning BeamTechnique

85. Scattering BeamTechnique
➢Itaims to produce a dose distribution witha flat lateralprofile.
➢The depth-dose curve with a plateau of adequate width is
produced by summing a number of Braggpeaks
➢Range modulation wheels consisting of variablethicknesses
ofacrylic glass or graphite steps are traditionally used for this
purpose.
➢Thewidthandthicknessofthemodulationwheelsare
calibrated to achieveSOBP.
➢ThewidthofSOBPiscontrolledbyturningthebeam off when
a prescribed width isreached.

86. Scattering BeamTechnique
➢Small fields: single scattering foil (made outof
Lead)
➢Larger field sizes: double-scattering system
(bi-material: High and low z material) to
ensure a uniform, flat lateral doseprofile
➢Modulatorwheel:variablethickness
absorbersin circular rotating tracks that
result in a temporal variation of the beam
energy

87. Scattering BeamTechnique

88. Range ModulatorWheel

89. Scanningbeam
technique
Double scattering
technique
Scattering BeamTechnique

90. Scanning BeamTechnique
➢As the pencil beam exits the transport system, it is
magnetically steered in the lateral directions to deliver dose to
a large treatment field.
➢The proton beam intensity may be modulated as the beam is
moved across the field, resulting in the modulated scanning
beam technique orIMPT
➢Current implementation of IMPT uses so called spot scanning
technique, in which the beam spot ismoved toalocationwithin
thetargetandtheprescribeddose is delivered to the spot, before
itismoved to the next spottodeliveritsprescribeddose.

91. Scanning BeamTechnique
➢Analternativetotheuseof
abroadbeamistogenerate
a narrow mono-energetic
"pencil" beam and to scan
it magnetically across the
target
➢Typicallythebeamis
scanned inazigzagpattern
inthe x-yplane
perpendiculartothebeam
direction

92. Scanning BeamTechnique

93. Scanning BeamTechnique

94. Advantage OfScanning
➢Incontrast to broad beam technique, arbitrary shapes of uniform
high dose regions can be achieved with a singlebeam
➢No first and second scatterers, less nuclear interactions and
therefore the neutroncontamination issmaller
➢Greatflexibility,whichcanbefullyutilizedin intensity-
modulated proton therapy(IMPT)
➢Disadvantage:Technicallydifficultand more sensitiveto
organmotionthanpassivescattering

95. TreatmentPlanning
❖Treatmentplanningforprotontherapyrequiresavolumetric
patientCT scandataset.
❖TheCTHUnumbersareconverted toprotonstoppingpower
values for calculating the proton range required for the treatment
field.
❖UncertaintiesintheconversionofCTnumberstoproton
stopping power in proton dose calculation translate into range
calculation uncertainties anderrors.

96. ❖Markingthe intended SOBP with a distal margin beyondthe
target and a proximal margin before the target in the range
calculation of each treatmentfield.
❖Other consideration in determining the marginsinclude target
motion, daily set up errors, beam delivery uncertainties and
uncertainties in the anatomy and physiologic changes in the
patient.
TreatmentPlanning

97. ➢The concept of PTV does not strictly apply to proton
therapy.
➢Incontrasttox-rayplanning,thePTVforproton therapy
isspecificforeachtreatmentfield.
➢Lateral margins are identical to traditionaldefinitions, but the
distal and proximal margins along the beam axis are
calculated to account for proton specific uncertainties.
TreatmentPlanning

98. Beam SpecificPTV
Accounted for three types ofuncertainties
❖GeometricalmissoftheCTVduetolateralsetup error
❖Range uncertainties accounted by giving proximalanddistal
margin
❖Rangeerrorcausedduetotissueheterogeneity

99. Steps For Beam SpecificPTV
An illustration of the four essential steps in creating the beam-specific targets
volume (bs PTV; red contour) from a clinical target volume (CTV; green
contour) with a dense object (grey sphere) along the beam path. (a) The CTV
is expanded laterally away from the beam axis using the expected motion
margin (IM) and setup margin (SM). (b) From a given beam angle, ray tracing
is performed to calculate the radiological path length of each ray from the
source to the both distal and proximal surface of the laterally expanded CTV
(blue contour). (c) The fraction of the total radiological range calculated in
previous stem is used to the distal margin per day. (d) Correction for interplay
effect of setup and range error is accounted by applying the correction kernel
and radiological path length margins are converted to physical depth margins.

100. Proton Dose Calculations
➢Pencil-beam algorithms are used for proton therapy dose
calculations.
➢They model proton interaction and scattering in various
heterogeneous media of the beam path, including the nozzle,
range compensators, and thepatient.
➢MonteCarlocalculationshasbeenusedtostudytheaccuracyof
suchdose calculation algorithms which indicates errors near
surfaces of media differing significantly in density and
composition, such as air cavity and bones

101. Application
❖Protontherapygoestoaspecificareaofthepatient'sbody,
sothistherapycanbestshrinktumorsthathavenotspreadto
otherpartsofthebody.
❖Protontherapy alone,ortheymay combinewith standard
radiation therapy, surgery, and/or chemotherapyareused
clinically.
❖Proton therapy is particularly useful for treating cancer in
children because it lessens the chance of harming healthy,
developingtissue.

102. Application
•Children may also receive proton therapy for some of the
rarest cancers affecting the spinal cord and brain (central
nervous system) and the eye, like orbital rhabdomyosarcoma
andretinoblastoma.
•It is quite useful in the treatment of tumor lying next to the
critically important tissues like optic nerves traveling
betweenthe brain and eye that required protection from the
radiation.

103. Proton Therapy May Be Used To Treat
These Cancers:
•Central nervous system cancers (includingchordoma,
chondrosarcoma, and malignantmeningioma)
•Eye cancer (including uveal melanoma orchoroidal melanoma)
•Head and neck cancers (including nasal cavityand paranasal
sinus cancer and some nasopharyngealcancers)
•Spinal and pelvic sarcomas (cancers that occur in thesoft-tissue
andbone)
•Some noncancerous tumors of the brain may also benefitfrom
protontherapy.

104. Proton Therapy May Be Used To Treat
These Cancers:
❖Pediatricmalignancies:
❖Craniospinal Axis Irradiation:Medulloblastoma
❖Craniopharyngioma
❖Lungcancer
❖Livercancer
❖Prostatecancer
❖Skull basetumors
❖Paranasal sinus tumors, Lymphomas, LungCancers
❖GI Malignancy: HCC, Pancreaticcancers

105. When Should We UseProtons?
➢Better organ sparing (Skull basetumors)
➢Better local control needed (CaProstate)
➢Late morbidity (Pediatricmalignancies)
➢Complex geometry (Ocularmelanoma)
➢Large target volume (ChildhoodMedulloblastoma)

106. PotentialApplications
➢Many publications have reported significant differences in
dose distribution
➢Reduction in the volume of non targeted receiving low-to
medium-range radiation doses.
➢In some cases, there is also a reduction inthe volume of non
targeted tissue receiving moderate-to high-doseirradiation.

107. Paranasal SinusTumors
Axial and sagittal
planes from
intensity-modulated
radiation therapy
(IMRT) plans are
shown on the left
and proton plans on
the right for a
paranasal sinus
tumor.

108. Head & Neck

109. Head & Neck
Conventional x-ray Advanced x-ray Advanced proton

110. Skull BaseSarcomas
Axial and sagittal
planes from
intensity-
modulated
radiation therapy
(IMRT) plans are
shown on the left
and proton plans
on the right for a
skull-base
sarcoma.

111. Craniopharyngioma
Axial and coronal
planes from intensity-
modulated radiation
therapy (IMRT) plans
(left), stereotactic
radiation therapy
(SRT) plans (center)
and proton therapy
plans (right) for a
small
craniopharyngioma.

112. Cranio-SpinalIrradiation
Sagittal planes from three
dimensional conformal
radiation therapy (3DCRT)
plans are shown on the left
and proton plans on the
right for craniospinal axis
irradiation necessary in a
variety of brain tumors,
most of which occur in
young patients at risk for
late effects.

113. Cranio-SpinalIrradiation

114. Lymphomas
Axial, coronal and
sagittal planes are
shown for 3DCRT
(left), IMRT (center),
and proton therapy
(right) for a female
patient with neck and
mediastinal
involvement by
Hodgkin lymphoma.

115. •Axial, coronal and
sagittal planes are
shown for 3DCRT
(left), IMRT
(center), and
proton therapy
(right) for patient
with lung cancer.

116. LungCancers

117. ProstateCancer
•Axial, coronal
and sagittal
planes of IMRT
(left) and proton
therapy (right)
plans for patient
with prostate
cancer.

118. ProstateCancer
http://www.pi.hitachi.co.jp/rd-eng/product/industrial-sys/accelerator-sys/proton-therapy-sys/proton-beam-therapy/index.html

119. Medulloblastoma
•Proto therapy plan
(Left) and standard
photon plan in a
case of
medulloblastoma

120. Breast

121. Proton Therapy of Cancer Breast
Coronal Axial

122. Proton range issues:
Reasons for range uncertainties
•Differences between treatment preparation and treatment
delivery (~ 1 cm)
•Daily setup variations
•Internal organ motion
•Anatomical/ physiological changes during treatment
•Dose calculation errors (~ 5 mm)
•Conversion of CT number to stopping power
•Inhomogeneities, metallic implants
•CT artifacts

123. Advantages: ProtonTherapy
When compared to standard x-ray radiation:
1.Improved dose distributions
2.Fewer short-and long-term side effects
3.Improved quality of life during and aftertreatment
4.Proven to be effective in adults andchildren
5.Reduces the likelihood of secondary tumors caused by
treatment
6.Can be used to treat recurrent tumors evenin patients
who have already receivedradiation

124. Advantages: ProtonTherapy
7.Targets tumors and cancer cells withprecision, reducing the
risk of damage to surroundinghealthy tissues andorgans
8.Reduction in integral dose to normaltissues
9.Reducedtoxicities
10.Dose escalation to tumors –increasedlocal control
11.Treat tumors close to critical organs; eye, spinalcord

125. Problems With ProtonTherapy
❖Patientrelated
➢Patient setup
➢Organmotion
➢Patientmovement
❖Physicsrelated
➢CT numberconversion
➢Dosimetry Machinerelated
❖Cumbersome
❖Cost

126. Drawbacks
•Limited availability-This treatment requires highly
specialized, expensive equipment. As a result, proton therapy
is available at just a few medical centers in the UnitedStates
•Higher expense-Proton therapy costs more than conventional
radiation therapy. equipment for production of protons,
neutrons and heavy ions is considerably more expensive than
standard radiotherapy equipment, both in capital costsand in
maintenance and servicingcosts.