Geant4 advanced example brachytherapy          last modified S.Guatelli 13/12/2002
 

Introduction


Brachytherapy is a widely used medical device for cancer treatment (What's brachytherapy).

The software is used by medical physicists to define the treatment planning in order to deliver a therapeutic dose to tumors, preserving the surrounding healty tissues (Role of softwares in brachytherapy) .

A software emploied to define the patient treatment planning must be rigourous and reliable for the cause of the delicate clinical use; the requirements for such a software are listed below.

The brachytherapic dosimetric software must:

  • be precise in the dose calculation;
  • reproduce the real geometry and tissues involved in the treatment (Computerised Thomography interface);
  • be fast in terms of computational time;
  • be simple to use (for hospitals!). 
  • The features of commercial softwares available, used commonly in the clinical practice, are showed in What kind of software is available in hospitals at present.

    Brachytherapy example development 



    The example has been  developed by:
        S. Agostinelli, S. Garelli , S. Guatelli, M.G.Pia, M. Tropeano with the medical physics consultancy of F. Foppiano.
     

    The brachytherapy advanced example follows the Unified Software Development Process; the rigorous software process adopted contributes to the quality of the product.
    The requested functionalities are listed in the User Requirements.
    The design is shown in Brachytherapy example design.
    Validation tests have been performed ( Tests ).
     

    Features of the brachytherapy example


    The result of the brachytherapy example is the dose calculation due to brachytherapic sources set inside a phantom.

    The brachytherapy example is generalised for all the brachytherapic thecniques.

    1.General  features shared by the different brachytherapic techniques.

    The application satisfies general functionalities which are shared by the different brachytherapic techniques:

  • it calculates the dose delivered in the phantom;
  • the isodose curves are obtained thanks to analysis instruments;
  • the user can choose the phantom materials interactively;
  • the user can visualize the experimental set-up.

  • 2.Particular aspects of each brachytherapic source

    The application satisfies also particular aspects of each brachytherapic device which consist in different source composition.
    The source is defined in the following terms:

  • in the geometry structure;
  • in the materials composition;
  • in the energy spectrum of the gamma delivered by the source. 
  • The feature of generalisation + specific aspect of the sources is obtained thanks to the use of the design pattern Abstract Factory.

    Thanks to the use of this design pattern, the source definition is completely trasparent: the user communicates with the abstract object BrachyVFactory, indipendently from the concrete sorce definition.
     

    The defined sources are:

  • the interstitial source Bebig Isoseed I-125;
  • the endocavitary source MicroSelectron HDR Ir-192;
  • Leipzig Applicator.
  • The user can define other brachytherapic sources without changing the example implementation.
     

    3.Physics

    The Geant4 Low Energy processes are activated for electrons and gamma.
     The Standard Processes are activated for positrons.
     

    4.Detector

    The phantom (sensitive detector) is devided in voxels (dimension=1mm);
    the energy deposit of a voxel is associated with the center of the voxel itself.
     

    5.Analysis

  • The energy deposit information is stored in a ntuple;
  • The energy deposit in the plain containg the source is stored in a 2D histogram;
  • The primary particles energy spectrum is stored in a 1D histogram;

  •   The results are stored in the file brachytherapy.hbk.

    The AIDA 3.0 toolkit is used for the analysis.
     

    How to run the application



      In the README of the application you will find the information about:
  • how to run the simulation;
  • how to switch the sources;
  • how to change the absorber material;
  • what is contained in the result of the simulation brachytherapy.hbk.
  • the environment set-up of the application is shown.

  •  

     

    Results of the simulation


    Example of results for all the brachytherapic techniques are shown in Results ;
    the information stored in the ntuple has been elaborated with analysis devices to obtain the histograms shown and the isodose curves.
     

    Future


    The next project involving the brachytherapy advanced example is the parallelisation of the system and the access to distributed calculation resources.

    As explained in What kind of software is available in hospitals at present, MonteCarlo simulations have never been used in the clinical practice because they are slow in terms of computational time, even if the dose calculation is more accurate.

    A solution to this problem is given by the parallelisation of the application and the access to distributed resources: in such a way institutes can share CPU and run the simulation in a parallelised way, even if their single CPU resources are poor.

    Collaborations


  • IST Genova
  • Servizio di Fisica Sanitaria Savona
  • Facolta' di Fisica  Genova
  • INFN Genova