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


Introduction


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: be precise in the dose calculation; reproduce the real geometry involved in the treatment; be fast in terms of computational time; be simple to use (for hospitals!). 

Medical linac example development 


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

Features of the medical linac example


The result of the medical linac example is the dose calculation given by a medical linac in a phantom filled with water.

1. General  features 

The main features of this example are

2. Geometry

The elements simulated are:

  1. The point source of electrons (the distribution of the electron energy and the electron radial intensity was assumed Gaussian in shape) (the beam is along the z axis)

  2. The primary collimator

  3. The target

  4. The vacuum window

  5. The flattening filter

  6. The ion chamber

  7. The mirror

  8. The secondary movable collimators (jaws)

  9. The light field reticle

  10. The phantom (filled with water)

The objects (2) and (3) are in a box filled with vacuum. The world volume is filled with air.

The primary particles (e-)  leave from a point source with random direction (0˚< θ < 0.3˚) and a gaussian distribution

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 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.

5. Analysis

The analysis part of Medical_Linac is based on the AIDA interface and its implementation on Anaphe.

The actual analysis produces some histograms; the histograms are saved at the end of the run in the file "medlinac.hbk".

 It contains:

  1. 2Dhistogram with the distribution of energy in the phantom (plane xz)
  2. 1Dhistogram with the primary particle energy 
  3. 2Dhistogram with the distribution of energy )at a depth in the phantom of 15 mm (ZThickness = 1. cm )
  4. 1Dhistogram with the distribution of energy along the z axis (Y and X Thickness = 5. mm), from which the user can calculate the PDD
  5. 1Dhistogram with the distribution of energy along the x axis (Y and Z Thickness = 5. mm) at a depth in the phantom of 15 mm, from which the user can calculate the flatness
  6. 1Dhistogram with the distribution of energy along the x axis (Y and Z Thickness = 5. mm) at a depth in the phantom of 50 mm, from which the user can calculate the flatness
  7. 1Dhistogram with the distribution of energy along the x axis (Y and Z Thickness = 5. mm) at a depth in the phantom of 100 mm, from which the user can calculate the flatness
  8. 1Dhistogram with the distribution of energy along the x axis (Y and Z Thickness = 5. mm) at a depth in the phantom of 200 mm, from which the user can calculate the flatness

How to run the application



In the README of the application you will find the information about:

Future


In next future I will put in this example the multi leaf collimator

   

Collaborations



Last modified 23 June 2004  - Michela Piergentili