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  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg

    1

    Master Thesis :

    The clinical performance of the DAVID-system for the

    in vivo verification of VMAT irradiation

    Presented by Mustafa Saibu Danpullo

    1st supervisor

    Prof. Dr.B.Poppe

    2nd supervisor

    Dr. HK. Looe,

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg2

    Layout

    I Introduction

    II Theory

    VMAT and IMRT

    MLC Design and Agility

    MWPC and DAVID system

    III Materials & Methods

    Equipment, alignment, patient data, stability of DAVID chamber

    Beam property, Error detection

    Deconvolution

    DAVID QA software

    IV Results / Discussion

    V Conclusion

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg3

    I Introduction

    IMRT (Intensity-modulated radiation therapy)

    VMAT (Volumetric Modulated Arc Therapy):

    Why In vivo verification ?

    ICRU report 24 (1976) recommended that certain types of tumors

    requires improve accuracy from 5% to 3.5%.

    To detect Equipment-related errors and deviations from the initial plan

    Complexity of planning and delivery techniques increases risk for

    treatment-related error incidents.

    In 1992 to 2007, more than 4,000 near misses without adverse

    outcome to patients case were reported, more than 50% were related

    to the planning or treatment delivery stage.

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg4

    In vivo dosimetry methods:

    in vivo intracavitary dosimetry with TLD

    Diodes

    DAVID (Device for Advanced Verification of IMRT deliveries

    In-vivo verification during treatment

    Online measurement of differences in dose to reference

    Error detection of the Multi Leaf Collimator (MLC)

    I Introduction

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg

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    II Theory

    Mostly Siemens, Elekta and Varian have introduced new LINAC

    control systems that will be able to change the MLC leaf positions

    IMRT uses many small fields to generated by beam-shaping

    devices (MLC) to deliver a single dose of radiation

    IMRT: Intensity-modulated Radiation Therapie

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg6

    II TheoryVMAT : Volumetric Modulated Arc Therapy

    VMAT is a rotational IMRT that can be delivered using

    conventional LINAC with MLC

    Elekta and Varian have introduced new LINAC control systems

    that will be able to change the MLC leaf positions and dose rate

    while the gantry is rotating.

    Precise Beam infinity and Rapid Arc

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg7

    A schematic drawing of the Siemens type A, Elekta type B and Varian type C MLC [18]

    Stepped leafs for different manufacturers [34]

    II Theory

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg8

    II Theory: Agility MLC design

    160 tungsten leafs,

    rounded arc edge,

    5 mm width,

    High speed(2x normal MLC) of up to

    3cm/sec,

    large field MLC enable clinicians to

    shape radiation,

    extremely low transmission of about

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg9

    Inventor:

    Prof. Georges Charpak,

    France,1968

    Nobel Prize in Physics (1992)

    II Theory: Multi wire proportional chamber (MWPC)

    The DAVID chamber is a multi-wire

    ionization chamber designed by PTW

    Freiburg based on Charpark's multi wire

    proportional chamber.

    http://store.aip.org/OA_HTML/ecl.jsp?mode=detail&item=6903http://store.aip.org/OA_HTML/ecl.jsp?mode=detail&item=6903

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg10

    Compton scattering Electric field causes electrons move to the

    anode(wire) and ionizied atoms/molecules to the

    cathode(plate)

    Each detection wire accumulates charge which

    loads a C.

    After the voltage at the capacitor is read out, it is set

    to zero and charged again

    The voltage achieved is read out by the associated

    amplifier at a rate of 1 Hz.

    Performed by multi-channel electrometer

    (MULTIDOS) + additional Software.

    II Theory: DAVID system functioning principle

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg

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    Signal interpretation:

    Ri: reading of a single channel (ion charge collected)

    C: cross section of the lengthy collection volume along the wire

    Ii: ionization density (x1 start of wire, x2 end of wire)

    li1-li2: aperture of the associated leave pair

    II Theory

    II Theory

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg

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    Front Plate

    Back Plate

    Air Volume

    II Theory: DAVID system signal recording

    3 groups of secondary electrons contributing to the signal:a)primary signal

    b)scattered signal

    c)leakage radiation

    (background signal)

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg13

    VMAT Planning:

    Treatment Planning System: ONCENTRA Masterplan Version 4.3

    ELEKTA Synergy accelerator with an Agility 80 leaf-pair MLC

    Desktop Pro TM 7.011 is Elekta's third generation fully integrated

    digital control system. MOSAIQ, DAVID software version 2.0

    DAVID T34065

    III Materials and Methods

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg14

    Patient data configuration chart

    III Materials & Methods

    Reference

    1st session

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg15

    DAVID Analysis

    PTW: DAVID 2.0 software

    III Materials & Methods

    Warning level: 3%

    Alarm level: 5%

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg16

    III Materials & Methods:

    VMAT: 4 (1 H&N, 3 Prostates)

    180 to -180 Clockwise and anti clockwise

    Stability of the DAVID system

    IMRT : 1 (Prostate)

    0

    90

    270

    (Prostate and Head and Neck) 14 days

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg17

    III Materials & Methods:The beam property of the DAVID chamber

    Percentage depth dose (PDD)

    Roos chamber 34001

    MP3 water phantom

    Transmission factor for 6 and 15 MV

    Semifex T31010 (Diff Field sizes)

    Setup conditions

    With and without DAVID

    SSD 100 and 80 cm

    Photon energy 6 and 15

    MV

    Different field sizes

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg18

    1. Successive opening of 1 leaf on 1

    side

    III Materials & Methods:VMAT Plan Editing for error detection

    MATLAB script to change the MLC-positions

    3. Field shift of a leaf gap (size of leave

    gap remains)

    2. Successive shift of a leaf gap (size of

    leave gap remains)

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg19

    1. Successive opening of 1 leaf on 1

    side

    VMAT Plan Editing for error detection

    MATLAB script to change the MLC-positions

    3. Field shift of a leaf gap (size of leave

    gap remains)

    2. Successive shift of a leaf gap (size of

    leave gap remains)

    III Materials & Methods:

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg20

    DeconvolutionIII Materials & Methods:

    S(x) measured signal as convolution of

    P(x) True dose profile with

    LRF f(x).

    S(x) = P(x) * f(x)

    van Cittert iterative deconvolution

    algorithm

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg21

    opened MLC at every 10th interval from 1st to 80th

    pairs.

    Nine MLC slit through the entire DAVID chamber

    IV Results and Discussion: Alignment

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg22

    IV Results and Discussion: Stability of DAVID System

    IMRT: prostate

    Deviation of 2% (+2%)

    VMAT: prostate

    Deviation of 1% (-1%)

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg23

    IV Results/Discussion: Stability of DAVID System

    IMRT: prostate

    Deviation of 2% (+2%)

    VMAT: H&N

    Deviation of

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University, Oldenburg24

    IV Results/Discussion: Transmission factor

    The average KDAVID

    0.939 0.003 for 6 MV

    and

    0.953 0.004 for 15 MV

    Reduction of dose at isocenter

    due to 8mm of PMMA

    By measuring the attenuation

    factor the output value can be

    corrected.

    Attenuation of the beam by the DAVID chamber

  • WG Medical Radiation Physics, Pius-Hospital and Carl von Ossietzky University,