[Gate-users] Strange Dose Profiles

[Ashok Tiwari]

Hi Chris, 

1. You should change the geometry of world volume because it should be large enough to include the entire simulation geometry. The tracking of any particle
stops when it escapes from the world volume. In your macro, I suggest you to increase X, Y and Z lengths not less than 250 mm ( you have phantom sphere radius of 125 mm, so length should be greater than diameter of spherical phantom). Checking with visualization wouldn’t be a bad idea to understand whats going on inside the world geometry. It might be the reason of discrepancy. 

2. I encourage you to check the best physics list mechanism based on the your Gate version and Geant4 version. For example: Geant4 10.3 version has emstandard_opt3 physics list EM constructors which was designed for applications that require higher accuracy of electrons ( as in dosimetry) and add Rayleigh scattering process for low energy electrons.

3. For dose actor definition: you are supposed to put any 2 combination, for example: you can define voxel size and resolution, or voxel size and Size, or resolution and Size. Gate automatically calculates the third parameter for you. 

4. For dose accuracy of beta emitters, say P-32, you are supposed to simulate the whole beta spectra. Google nuclear database (e.g.; Nudat) and pull out beta spectrum information and use it to define the discrete spectrum. I’m attaching spectrum of P-32 in the following lines:

#### P-32 beta spectrum #####
1	0
0.0428  3.03E-02
0.1283  4.38E-02
0.2138  5.50E-02
0.2994  6.43E-02
0.3849  7.17E-02
0.4704  7.70E-02
0.5559  8.02E-02
0.6414  8.11E-02
0.7270  8.00E-02
0.8125  7.68E-02
0.8980  7.16E-02
0.9835  6.48E-02
1.0690  5.66E-02
1.1546  4.74E-02
1.2401  3.76E-02
1.3256  2.78E-02
1.4111  1.85E-02
1.4966  1.03E-02
1.5822  4.09E-03
1.6677  8.09E-04

If you do not know the meaning of 1 and 0 in the above spectrum then read the Gate manual carefully.

I hope this helps.


Regards, 
Ashok Tiwari



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