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

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

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

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  1. 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 isdelivering 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. ProblemStatement 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. simulation General plan 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), thelateral 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. 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 31002 Flexible. IAEA 398

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

  12. Comparison with experimental data Voxels 1mm Voxels 5mm 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 precision • Low-cost dosimetric system • Package Low Energy • Validation of physical processes in Geant4 • Comparison with experimental measurements 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

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