Presentazione di PowerPoint

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Medical Linac
F. Foppiano, M.G. Pia, M. Piergentili
Geant4 Workshop 2004 Catania
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Radiotherapy with external beam
A cancer or a tissue near a tumour surgically
removed, have to be irradiated with gamma rays in
order to reduce the tumour dimension or to
sterilize the zone
Cancer cells are more sensitive to radiation
damage compared to healthy cells
Varian Clinac 2100 CD
The goal of radiotherapy is delivering the
required therapeutic dose to the tumor area with
high precision, while preserving the surrounding
healthy tissue
Accurate dosimetry is at the basis of
radiotherapy treatment planning
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Intensity modulated radiation therapy
new
Progress in 3D medical imaging

• Beam aperture is shaped to the irregular form of
  the target
• Photon fluencies are modulated

step and shoot

• Dose distribution more homogeneous within the
  PTV
• Much sharper fall-off of dose at PTV boundary
• Inhomogeneous dose distribution to treat concave
  surface

Head and neck breast prostate
Normal tissues exposed to high doses can be
reduced
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Problem Statement
determine the dose distributions given in a
phantom by the head of a linear accelerator
Dosimetric system
Commercial systems
speedy, but contain approximations
Analytic algoritms
Es. Eclipse, Plato
Accurate modelisation of the experimental set-up
Dose distribution in a phantom
speedy
precise
Easily to configure
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General plan
simulation
analysis

Geant4
planning and developing the dosimetric system
AIDA/Anaphe

• functionalities
• design
• Advanced software

OO tecnology
Specific software process
DIANE

• Microscopic validation of Geant4 processes
• Dosimetric validation of the sistem
• Experimental measurements

Validation of the dosimetric system
Statistical toolkit
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Dosimetric system

• Gaussian distribution for energy and momentum of
  primary particles
• Each pair of jaws can be rotated through an axis
  that is perpendicular to the beam axis
• The user can choose the position of every single
  leaf

• The actual analysis produces some histograms from
  which the user can calculate the Percent Depth
  Dose (PDD), the lateral profiles at the following
  depths in the phantom 15 mm, 50 mm, 100 mm and
  200 mm, and the isodoses curves in a plane

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Flattening filter
Dosimetric system
Primary collimators and target
MLC
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Design
Decorator

• Flexibility
• Extensibility
• Distributed responsibility

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Software tecnologies
iterative and incremental approach
Based on use cases
Software process artifacts
Mapped on ISO 15504
Dinamic and static dimension
Rational Unified Process
Specific software process for this dosimetric
system
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Experimental measurements with ion chamber
Percent Depth Dose
Squared fields 5x5 cm, 10x10 cm, 40x40 cm
PTW MP3
PTW 31002 Flexible.
IAEA 398
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Comparison with experimental data
? 1010 events ? 100 CPU days on Pentium IV 3 GHz
Kolmogorov-Smirnov test
range D p-value
-56 ? -35 mm 0.26 0.89
-34 ? -22 mm 0.43 0.42
-21 ?21 mm 0.38 0.08
22 ? 32 mm 0.26 0.98
33 ? 36 mm 0.57 0.13
range D p-value
-84 ? -60 mm 0.385 0.23
-59 ? -48 mm 0.27 0.90
-47 ? 47 mm 0.43 0.19
48 ? 59 mm 0.30 0.82
60 ? 84 mm 0.40 0.10
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Comparison with experimental data
Voxels 1mm
Voxels 5mm
range D p-value
0 ? 14 mm 0.548 0.09
15 ? 300 mm 0.144 0.123
D 0.005 p-value 1
Kolmogorov-Smirnov test
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Experimental measurements with radiographics films
Grey tone
Optical density
Dose
Field used to treat prostate cancer
Kodak X-Omat V films Scanner VXR16 Dosimetry
Pro Software Rit 113
Spatial resolution 89 ?m
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Comparison with experimental data
Dose distribution in a plane (dosimetric system)
Isodose lines (dosimetric system)
Isodose lines (RIT113)
film
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Conclusions

• Low-cost dosimetric system
• Package Low Energy
• Validation of physical processes in Geant4
• Comparison with experimental measurements

precision
Future improvements

• Phase space
• Dynamic tecnique

This is an Advanced Example of
Submission of a paper to IEEE Transaction on
Nuclear Science
Thanks to Barbara Mascialino for the statistical
analysis