Medical Linac advanced example The example has been developed by: M.Piergentili with the help of M.G.Pia and F.Foppiano Acknowledgments to GEANT4 people, in particular to A. Mantero and S. Guatelli |
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This Geant4 advanced example simulates a typical linear accelerator used for radiation therapy, in particular IMRT.
In medical application, distribution doses are useful because indicative of the quantity of radiations absorbed by tissues. Many algorithms were developed to estimate the dose distributions, but the more sophisticated ones resort to some approximations too. These approximations might affect the outcome of dose calculation, specially in a complex treatment planning as Intensity Modulated Radiation Therapy (IMRT). A MC method, simulating particles interactions through the matter, is more precise in computing dose distributions.
The term IMRT refers to a particular radiation therapy whose principle is to treat a patient from a number of different directions with beams of non uniform fluences, which have been optimized to deliver a high dose to the target volume and acceptably low dose to the surrounding healthy tissues.
This microscopic control allows IMRT to produce dose distribution patterns that are much closer to the desired patterns than possible previously.
A software emploied to verify 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.
This dosimetric software
must:
The medical linac advanced example
follows the Unified Software Development Process; the rigorous software process
adopted contributes to the quality of the product.
The requested functionality is listed in the User
Requirements .
The
design is shown in Medical Linac example
design
- Calculation of the dose delivered in the phantom;
- The user can visualize the experimental set-up.
- Macros for the visualization of geometry and tracks with OpenGL, VRML and DAWN drivers.
- Implementation of messengers to change the positions of the secondary collimators and to select the mean energy ad the standard deviation of the electrons delivered by the point source.
The elements simulated are:
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The objects (2) and (3) are in a box filled with vacuum.
The primary particles (e-) leave from a point source with random direction (0˚< θ < 0.3˚) and a gaussian distribution
The Geant4 Low Energy processes are
activated for electrons and gamma.
The Standard Processes are activated for
positrons.
The phantom (sensitive detector) is divided in voxels (dimension=1mm);
the energy deposit of a voxel is associated with the center of the
voxel itself.
The distance between the upper surface of the target
and the upper surface
of
the phantom (SSD) is 100 cm.
The actual analysis produces some histograms; the histograms
are saved at the end of the run in the file "medlinac.hbk".
It contains:
In next future I will put in this example the multi leaf collimator
Collaborations