Topics Covered PROTON Physics and Technology ?· Topics Covered • Rationale for ... electronic collisions…

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  • 1

    PROTON Physics and

    Technology

    Alfred Smith, Ph.D.M. D. Anderson Cancer Center

    Houston, TX

    Topics Covered

    Rationale for Proton Therapy

    Physics of Proton Beams

    Treatment Delivery Techniques

    Proton Therapy Technology

    Rationale for Proton Therapy

    Need for Improved Local Control in Cancer Treatment (selected sites)

    (all numbers are estimates)

    Head/Neck 22,000 13,200 (60%)Gastrointestinal 135,000 54,000 (40%)Gynecologic 28,000 14,000 (50%)Genitourinary 55,000 27,500 (50%)Lung 160,000 40,000 (25%)Breast 41,000 4,920 (12%)Lymphoma 20,000 2,400 (12%)Skin, Bone, Soft Tissue 15,000 5,000 (33%)Brain 12,000 10,800 (90%)

    Total 488,000 171,820 (35%)

    Over 1,350,000 new cancer patients per year in the US

    Tumor Site Deaths/ Deaths due toyear Local Failure

  • 2

    Dosimetric advantages of proton beams

    Protons Stop! Photons dont stop. Proton dose at depth

    (target) is greater than dose at surface.

    Photon dose at depth (target) is less than dose at dmax.

    Protons

    Ideal dose distribution

    Photons

    Photons

    Protons

    PHOTONS

    PROTONS

    MEDULLOBLASTOMA

    100

    60

    10

    PHOTONS

    PROTONS

    Advantages of Proton Therapy

    Highly localized dose distributions Increased local control of tumors Decreased treatment-related side effects Improved Quality of Life

    Proton Physics

    Protons lose energy by:

    ionizations

    multiple Coulomb scattering

    non-elastic nuclear reactions.

  • 3

    Electromagnetic energy loss of protons

    e

    pp

    Mass Electronic Stopping Power is the mean energy lost by protons in electronic collisions in traversing the distance dx in a material of density .

    S/ = 1/[dE/dx] 1/v2Where v = proton velocity

    This is the main interaction that causes formation of Bragg peak.

    0%

    20%

    40%

    60%

    80%

    100%

    120%

    0 5 10 15 20 25 30

    Depth in Water[cm]

    Rel

    ativ

    e D

    ose

    [%]

    1. The incident beam has a narrow energy spread (E/E 0.2%)

    2. Bragg peak is broadened by range straggling (statistical differences in energy losses in individual proton paths).

    A certain fraction of protons undergo nuclear interactions, mainly on 16O ( 1%/cm)

    Nuclear interactions lead to secondary particles and thus to local and non-local dose deposition, including neutrons.

    Nuclear interactions of protons

    n

    p

    pp

    p

    Primary fluence

    Effect on the lateral dose distribution

    Secondaries from nuclear interactions

    Pedroni et al PMB, 50, 541-561, 2005

    Depth in Water [cm]

    0 5 10 15 20 25 30 35

    Rel

    ativ

    e D

    ose

    [%]

    0102030405060708090

    100110

    Total Absorbed Dose

    'Primary' Dose 'Secondary' Dose

    230 MeV protons

    Effect on Depth Dose

    Normalized (at peak) Bragg Curves for Various Proton Incident EnergiesRange Straggling will cause the Bragg peak to widen with depth of penetration

    0

    0.2

    0.4

    0.6

    0.8

    1

    1.2

    0 5 10 15 20 25 30 35 40

    Depth in Water (cm)

    Rel

    ativ

    e D

    ose

    100 MeV130 MeV160 MeV180 MeV200 MeV225 MeV250 MeV

    -10

    0

    10

    20

    30

    40

    50

    0 10 20 30 40 50

    Depth in Water (cm)

    100 MeV

    130 MeV

    160 MeV

    180 MeV

    200 MeV

    225 MeV

    250 MeV

    Normalized (at entrance) Bragg Curves for Various Proton Incident Energies

    Rel

    ativ

    e D

    ose

  • 4

    Dose depositions in water from 160 MeV protons. Beam slit delimiters with width W cm.

    Uniform particle distributions.

    0

    5

    10

    15

    20

    25

    30

    0 5 10 15

    Depth (cm)

    Dos

    e (M

    eV/c

    m)

    W = 0.1 cmW = 0.16 cmW = 0.24 cmW = 0.5 cmW = 1 cmW = 2 cm

    Depth dose for 160 MeV Protons for various field sizes

    For small fields, loss of in-scattering (charged particle equilibrium) results in deterioration of Bragg peak and non uniformity of SOBP.

    Protons undergo multiple deflections through elastic coulomb interactions with atomic nuclei

    Beam broadening can be approximated by a Gaussian distribution

    pp

    Multiple Coulomb Scattering (MCS) leads to broadening of lateral penumbra as beam penetrates in depth.

    0.0

    0.2

    0.4

    0.6

    0.8

    1.0

    1.2

    -150 -100 -50 0 50 100 150Off-axis Distance (mm)

    Rel

    ativ

    e D

    ose

    Depth=8 cmDepth=15.9 cmDepth = 12 cm

    Lateral penumbra: Dominated by Multiple Coulomb Scattering d80-20 1.68 3.3% of range 5 mm at 15 cm depth Wide angle scattering and nuclear interaction products add Total penumbra 6-7 mm at 15 cm depth

    8 cm depth

    16 cm Depth

    12 cm Depth

    80/20 Penumbra Comparison

    0.00

    0.25

    0.50

    0.75

    1.00

    15 cm 20 cm 25 cm

    Norm alization Depth

    80 -

    20 %

    Dis

    tanc

    e (c

    m)

    Lateral dose fall-off: Protons vs. Photons

    15 MV Photons

    Protons

    17 cm

    Paganetti

  • 5

    Urie

    Large air gaps will degrade the lateral penumbra

    Proton Therapy Beam Delivery Technology

    Physics of the Passive Scattering Mode of Proton Beam Delivery

    Goitein, Lomax, Pedroni - Med. Phys.

    Passive Scattering Nozzle with Range Modulation Wheel

    Hitachi Passive Scattering Nozzle

  • 6

    How a Spread Out Bragg Peak (SOBP) is formed. Modulation wheel rotates in the

    beam. Pull-back (energy shift)

    determined by height of step. Weight determined by width of

    step. Multiple SOBPs can be obtained

    by gating beam.

    Deficiencies of Proton Passive Scattering Techniques

    Excess normal tissue dose.

    Increases effective source size

    which increases lateral

    penumbra.

    Requires custom aperture and

    compensator

    Inefficient - high proton loss

    produces activation and

    neutron production.

    Chu, Ludewigt, Renner - Rev. Sci. Instrum.

    PTCOG 46 Educational Workshop

    Prostate Patient Treatment Plan

    CTVRectumBladderFemoral heads

    Al Smith PTCOG 46 Educational Workshop

    QA of Prostate Treatment using patient treatment parameters/appliances and EBT film in water

    phantom.Treatment plan on CT anatomy converted to dose distribution in water phantom.

    PTCOG 46 Educational Workshop

    Measurements in water phantom using EBT film, patient aperture, and range compensator

    Cross Field Profile A to P through Isocenter

    0

    0.2

    0.4

    0.6

    0.8

    1

    -65 -45 -25 -5 15 35 55

    Lateral Distance (mm)

    Dose

    (arb

    uni

    ts)

    EBT film measurement

    Eclipse

    Cross Field Profile F to H through isocenter

    0

    0.2

    0.4

    0.6

    0.8

    1

    -70 -50 -30 -10 10 30 50 70

    Lateral Distance (mm)

    Dos

    e (a

    rb u

    nits

    )

    EBT film measurementEclipse

    Al Smith PTCOG 46 Educational Workshop

    Patient Treatment QA Measurements compared with treatment planning calculations converted to water phantom.

    Eclipse vs. Measured - Crossplane

    0

    20

    40

    60

    80

    100

    0 2 4 6 8 10 12

    Eclipse Measured

    Data measured in water phantom using Pin-Point ion chamber. Treatment aperture and range compensator were both inserted.

    Al Smith

    The Pencil Beam Scanning Mode of Proton Beam Delivery

    Goitein, Lomax, Pedroni - Med. Phys.

  • 7

    Beam3.2m

    ScanningMagnets

    Profile Monitor

    CeramicChamber

    Spot Position Monitor

    Dose Monitor 1, 2

    Energy AbsorberIsoCenter

    Energy Filter

    PerformanceRange 4 36 g/cm2

    Adjustability 0.1 g/cm2

    Max. field size 30 x 30 cm

    Beam size in air 5 10 mm

    SAD > 2.5 m

    Dose compliance +/- 3% (2 )

    Irradiation time < 1.5 min to deliver 2 Gy to 1 liter at any depth.

    Pencil Beam Scanning Nozzle

    HeliumChamber

    Hitachi Spot Scanning Nozzle

    A major problem with spot scanning:The target can move during treatment leading to dose errors!

    Remedies:Rescanning (spot, layer, volume)

    D/D 1/n, where n = number of scansBeam GatingReal time tracking with markers

    Orthogonal IC array measurements performed at different water depths using a computer controlled water column and

    compared with calculations.

    Beams-eye-view of dosein water

    U axis profile

    T axis profile

    Pedroni, PSI, Switzerland

    PTCOG 46 Educational Workshop

    Ionization Chamber ArrayWater column with 26 small ionization chambers of 0.1 cm3

    Dose box

    Pedroni, PSI, Switzerland

    Beam

    Mirror

    CCD Camera

    Scintillating Plate

    Scintillating Plate, Mirror and CCD Camera used for pencil beam scanning QA.

    Spot Pattern Test Uniform Field Scanning Test

    M D Anderson Cancer Center

    PTCOG 46 Educational Workshop

    Scintillating screen viewed with a CCD through a 45 mirror

    ideal for non homogeneous dose distributions

    WER6.65CM

    WER7.82CM

    W= 6.65 cm

    W= 7.82 cm

    Calculation Measurement vs.

    Pedroni, PSI, Switzerland

    Martin Bues

    1. Proton Accelerators2. Isocentric Gantries

    3. Typical Facility

  • 8

    Accelerators used in proton therapy facilitiesIBA 230 MeV CyclotronHitachi 250 MeV synchrotron

    Varian/ACCEL Superconducting Cyclotron

    250 MeV; 90 tons; 3.2 m dia.

    Still River Superconducting Synchrocyclotron

    250 MeV; 20 tons; 1.7 m dia.

    220 tons

    63 tons8 m dia.

    ProTom International Inc.A Scanning-Optimized Synchrotron

    Total weight = 15 tons; 4.9 m diameter 330 MeV Proton tomography 0.1 to 10 sec extraction Variable intensity

    Hitachi

    M. D. Anderson Gantry

    Siemens

    Heidelberg

    600 tons

    190 tons

    120 tons

    Proton

    Carbon

    Gantries

  • 9

    Accelerator mounted on Gantry

    Entire system contained in one room

    Multiple independent rooms can be installed

    Still River

    Proton Therapy System

    Typical Proton Therapy Facility

    12

    5

    43

    6

    1. Accelerator 4. Gantry room

    2. Beam transport line 5. Fixed beam room

    3. Gantry room 6. Patient support area

    PHASE llAdd Light ions

    Phase I Protons only

    A Proton + Light Ion Facility built in two phases

    Robotic Applications

  • 10

    New Technologies

    Laser Accelerated Proton BeamsProton acceleration is achieved by focusing a high-power laser on a thin target. The short (10-16 sec) laser pulse width produces a high peak power intensity that causes massive ionization in the target, expelling a large number of relativistic electrons. The sudden loss of electrons gives the target a high positive charge and this transient positive field accelerates protons to high energies.

    5 m laser system

    Proton beam source

    Laser accelerated proton therapy has a time frame of 5 10 years.

  • 11

    Dielectric Wall Proton Accelerator (DWA)

    Conventional accelerator cavities have an accelerating field only in the gaps which occupy only a small fraction of their length. In a DWA, the beam pipe is replaced by an insulating wall so that protons can be accelerated uniformly over the entire length of the accelerator yielding a much higher accelerating gradient.

    Artist Concepts for DWA clinical installation

    The goal is to have a full scale prototype in ~ 4-5 years, which will be installed at UC Davis CC.

    Thomotherapy is the private sector partner

    Thank You!

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