F. Foppiano, M.G. Pia, M. Piergentili

Medical Linac

Geant4 Workshop 2004 Catania

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

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

Varian Clinac 2100 CD

Intensity modulated radiation therapy

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

Progress in 3D medical imaging

Normal tissues exposed to high doses

can be reduced

Beam aperture is shaped to the irregular form of the target

Photon fluencies are modulated

Head and neckbreast

prostate

Dosimetric system

Commercial systems

Analytic algoritmsAnalytic algoritmsEs.: Eclipse, Plato

speedy, but contain approximations

precise

Accurate modelisation of the experimental

set-up

Dose distribution

in a phantom

Easily to configure

speedy

Problem Statement

determine the dose distributions given in a phantom by the head of a linear accelerator

General plan

Geant4

AIDA/Anaphe

OO tecnology

Specific software process

functionalities design Advanced

software

Microscopic validation of Geant4 processes

Dosimetric validation of the sistem

Experimental measurements

Validation of the

dosimetric system

planning and developing the

dosimetric system

simulation analysis+

DIANE

Statistical toolkit

Dosimetric system

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

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

Dosimetric system Flattening filter

MLC

Primary collimators and target

Design

FlexibilityExtensibilityDistributed responsibility

DecoratorDecorator

Software tecnologies

Mapped on ISO 15504

Dinamic and static dimension

Based on use cases

Rational Unified Process

Specific software process for this dosimetric system

Software process artifacts

Experimental measurements with ion chamber

IAEA 398

Percent Depth Dose

Squared fields 5x5 cm, 10x10 cm, 40x40 cm

PTW 31002 Flexible.

PTW MP3

Comparison with experimental data

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

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

Kolmogorov-Smirnov testKolmogorov-Smirnov test

1010 events

100 CPU dayson Pentium IV 3 GHz

Comparison with experimental data

D = 0.005; p-value = 1

range D p-value

0 14 mm 0.548 0.09

15 300 mm

0.144 0.123

Kolmogorov-Smirnov test

Voxels 5mmVoxels 1mm

Experimental measurements with radiographics films

Kodak X-Omat V filmsScanner VXR16 Dosimetry ProSoftware Rit 113

Grey tone Optical density Dose

Spatial resolution = 89 m

Field used to treat prostate cancer

Comparison with experimental data

filmDose distribution

in a plane (dosimetric

system)

Isodose lines (RIT113)

Isodose lines (dosimetric system)

Conclusions

• Low-cost dosimetric system

• Package Low Energy • Validation of physical processes

in Geant4• Comparison with experimental

measurements

Future improvements

• Phase space• Dynamic tecnique

Thanks to Barbara Mascialino for the statistical analysis

This is an Advanced Example of

precision

Submission of a paper to IEEE Transaction on Nuclear Science