## 1.1. General concept¶

The Radiotherapy and Dosimetry reference paper GATE V6: a major enhancement of the GATE simulation platform enabling modelling of CT and radiotherapy is available here. If you are interested in Gate simulations in a clinical environment for light ion beam radiotherapy, then you may want to have a look at GateRTion

A list of radionuclides is availabe at NUCLEIDE.ORG.

The concept of Actors is very important for the simulation of radiotherapy treatments and dosimetry. Tools to Interact with the Simulation : Actors and MuMapActor are tools which allow to interact with the simulation. They can collect information during the simulation, such as energy deposit, number of particles created in a given volume, etc. They can also modify the behavior of the simulation. There are different types of actors which collect different types of information, however some commands and behavior are common to all actors. To use selection criteria, it is possible to add filters.

## 1.2. Insert a CT image in the therapy simulation¶

For a realistic radiotherapy simulation, one wants to use a patient CT image as the voxelized phantom. For that, the following steps must be followed.

### 1.2.1. Step1: convert Dicom image to Analyze image file format¶

The vv, the 4D Slicer software can be used for this purpose. It opens the DICOM image and saves it as a header plus raw data. It can also resample the image.

### 1.2.2. Step2: define HU to materials conversion¶

The following macro can be used to generate Hounsfield Unit (HU) to material conversion:

/gate/HounsfieldMaterialGenerator/SetMaterialTable                       MaterialsTable.txt
/gate/HounsfieldMaterialGenerator/SetDensityTable                        DensitiesTable.txt
/gate/HounsfieldMaterialGenerator/SetDensityTolerance                    0.1 g/cm3
/gate/HounsfieldMaterialGenerator/SetOutputMaterialDatabaseFilename   myimage-HUmaterials.db
/gate/HounsfieldMaterialGenerator/SetOutputHUMaterialFilename            myimage-HUmat.txt
/gate/HounsfieldMaterialGenerator/Generate


### 1.2.3. Step3: insert image as a volume¶

Example:

/gate/world/daughters/name                    patient
/gate/world/daughters/insert                  ImageNestedParametrisedVolume
/gate/patient/geometry/SetImage               myimage.hdr
/gate/geometry/setMaterialDatabase            myimage-HUmaterials.db
/gate/patient/geometry/SetHUToMaterialFile    myimage-HUmat.txt
/gate/patient/placement/setTranslation        0 0 0 mm


## 1.3. Dose distribution (Dosimetry)¶

GATE allows to simulate the dose distribution in a phantom during radiotherapy (therapy with photons) and hadrontherapy (therapy with hadrons : proton, Carbon…). It also allows to perform other radiation simulations such as brachytherapy, dose deposited during x-ray imaging… Fig. 1.24 shows an example of a dose distribution map obtained after radiotherapy treatment on a phantom.

The Dose measurement (DoseActor) is the tool that is used to store the deposited dose in a 3D matrix which size and resolution can be specified. It can also be used for 1D and 2D dose maps. It can store dose, edep or number of hits and computes associated statistical uncertainty. The DoseActor is attached to a volume which can be voxelized or not.