1. F. Foppiano, M.G. Pia, M. Piergentili
Medical Linac
F. Foppiano, M.G. Pia, M. Piergentili
Geant4 Workshop 2004 Catania

2. 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

3. 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

4. Accurate modelisation of the experimental set-up
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

5. + General plan simulation analysis
Geant4
planning and developing the dosimetric system
functionalities
design
Advanced software
AIDA/Anaphe
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

6. 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

7. Flattening filter
Dosimetric system
Primary collimators and target
MLC

8. Design
Decorator
Flexibility
Extensibility
Distributed responsibility

9. Rational Unified Process
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

10. Experimental measurements with ion chamber
Percent Depth Dose
Squared fields 5x5 cm, 10x10 cm, 40x40 cm
PTW MP3
PTW Flexible.
IAEA 398

11. Comparison with experimental data
 1010 events
 100 CPU days
on Pentium IV 3 GHz
Kolmogorov-Smirnov test
Agreement more suitable
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
0.98
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

12. 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

13. 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

14. Comparison with experimental data
Dose distribution in a plane (dosimetric system)
Isodose lines (dosimetric system)
Isodose lines (RIT113)
film

15. Conclusions Future improvements
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