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Brachytherapy at IST Results from an atypical Comparison Project

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Title: Brachytherapy at IST Results from an atypical Comparison Project


1
Brachytherapy at ISTResults from an atypical
Comparison Project
  • Stefano Agostinelli1,2, Franca Foppiano1,
    Stefania Garelli1, Matteo Tropeano1
  • 1National Institute for Cancer Research and
    2Physics Dept. Univ. of Genova
  • Petteri Nieminen Maria Grazia Pia

2
History
3
What is brachytherapy?
  • Brachytherapy is a medical therapy used for
    cancer treatments
  • Radioactive sources are used to deposit
    therapeutic doses near tumors while preserving
    surrounding healthy tissues

After-loading unit
  • In HDR endocavitary brachytherapy
  • a radioactive source, for example 192Ir, is used
  • the source moves along catheters inserted in
    natural cavities of the body, e.g. vagina or
    bronchi this allows the deposition of the
    therapeutic tumor dose right where it is needed
  • the source track is programmed by an
    after-loading unit

Catheter along which source moves
4
Brachytherapy treatment planning
  • A typical vaginal treatment plan source moves
    along a single catheter

A typical intra-uterine treatment plan the
source moves along 3 catheters
5
Monte Carlo for brachytherapy
  • Monte Carlo simulation topics for brachytherapy
  • Dose calculation
  • Computation of dose deposition kernels for
    treatment planning dose calculation algorithms
    based on convolution/superposition methods
  • Separation of primary, first scatter and multiple
    scatter components for complex dose deposition
    models
  • Computation of other model-dependent parameters,
    e.g. anisotropy function
  • Accurate computation of dose deposition in high
    gradient regions (i. e. near sources)
  • Verification of experimental calibration
    procedures

6
Comparisons with data
Full simulation of the radioactive source
Simulation of a simple set-up
  • Simulated water ???
  • (photon attentuation coefficient)
  • Comparison of NIST data with Geant4
  • Standard electromagnetic package
  • and Low Energy extensions results

Comparison with in-house experimental data and
certifications of the supplying company
Low Energy/Standard e.m. Physics packages ESA
Radioactive Decay Module
Tests of
7
Comparisons with full source simulation
Anisotropy Comparisons with published reference
treatment planning data
Air kerma rate at various distances Comparisons
with measurements of the air kerma rate at IST,
following the Protocol for the Basic Dosimetry in
Radiotherapy with Brachytherapy Sources of the
Italian Association of Biomedical Physics
Isodoses Comparisons with tabulated isodoses for
superficial brachytherapy applicators
8
Photon attenuation coefficient, Water
Comparison of Geant4 LowE/standard e.m. processes
and NIST data
(Statistical errors are smaller than dot size)
9
Photon attenuation coefficient, Fe
Comparison of Geant4 LowE/standard e.m. processes
and NIST data
(Statistical errors are smaller than dot size)
10
Photon attenuation coefficient, Pb
Comparison of Geant4 LowE/standard e.m. processes
and NIST data
Photons are all absorbed with Standard below 100
keV
(Statistical errors are smaller than dot size)
11
Description of ?-Selectron 192Ir source
  • Geant4 allows complete flexible description of
    the real geometry
  • 192Ir energy spectrum
  • currently described as monochromatic at 356 keV
  • will soon be described by the ESA Geant4
    RadioactiveDecay class

12
Simulation of dose deposition in water
  • The simulated source is placed in a 30 cm water
    box
  • The dose deposition is investigated in the
    longitudinal plane
  • The plane is partitioned in 1 million 1mm3 voxels
  • A minimum of 10 millions photons are generated on
    the 4? solid angle

?-Selectron 192Ir source
Longitudinal plane partitioned in cells
13
Investigated quantities anisotropy
  • The dose deposition is not isotropic due to
    source geometry and auto-absorption,
    encapsulation and shielding effects
  • Anisotropy can be described by a simple angular
    function which can be computed by re-sampling our
    simulated voxels grid calculations

14
Investigated quantities isodoses
  • The simulated dose deposition data can also be
    used to derive isodoses

15
Products of this Comparison Project
  • Tests of Geant4 LowE/standard e.m. processes
  • Tests of the Geant4 Radioactive Decay Module
  • A physics test (m/r) to become part of regular
    LowE testing
  • An Advanced Example to be released to the user
    communities
  • The porting of Geant4 2.0 to Windows/Cygnus
  • 4 common presentations at conferences so far
  • 2 common publications in preparation ( IST
    groups ones)
  • A wide promotion of Geant4 in the medical
    environment
  • A contribution to technology transfer

16
Conclusions and future goals
  • This Comparison Project has already generated
    valuable products
  • The activity of the experimental group and of the
    Geant4 collaborators are fully integrated, with
    mutual benefit
  • Further developments and comparisons are planned
    in the next weeks
  • More realistic description of 192Ir source energy
    spectrum with the new Geant4 RadioactiveDecay
    class
  • Comparison with in-house data
  • Simulation of shielded brachytherapy applicators

Many thanks to Gabriele Cosmo and Alessandro
Brunengo for their invaluable help!
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