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Question about step limitation in Hadrontherapy  

Forum: Medical Applications
Date: 11 Mar, 2008
From: <jfgao@mdanderson.org>

Dear G4 Developers:
I try to simulate protons irridiating a nanometer scale sphere ( diameter 
40 nm). In the visulation, I can see the protons and secondary electrons
going around the nanosphere. But when I collect the energy depositted in
my 40 spherical sensititive detectors (  ridius range from 0-80 nm),
there is always two high peaks around the surface even the materials 
incide and outside nanometer sphere are same. Then I check the tracking 
information and I found the proton info is resonable as following several
steps,
   
 *********************************************************************************************************
* G4Track Information:   Particle = proton,   Track ID = 1,   Parent ID = 0
*********************************************************************************************************

Step#    X(mm)    Y(mm)    Z(mm) KinE(MeV)  dE(MeV) StepLeng TrackLeng  NextVolume ProcName
    0   -4e-05 -2.74e-06 1.19e-05      2.53        0        0         0 PhantomNPhys initStep
    1 -2.62e-05 -2.75e-06 1.19e-05      2.53  1.2e-05 1.38e-05  1.38e-05 PhantomNPhys msc
    2 -1.59e-05 -2.75e-06 1.19e-05      2.53 2.03e-05 1.03e-05  2.41e-05     NanoPhy Transportation
    3 -6.8e-06 -2.75e-06 1.19e-05      2.53 0.000109 9.07e-06  3.32e-05     NanoPhy msc
    4 2.26e-06 -2.75e-06 1.19e-05      2.53 3.05e-05 9.07e-06  4.23e-05     NanoPhy msc
    5 1.13e-05 -2.74e-06 1.19e-05      2.53        0 9.07e-06  5.13e-05     NanoPhy msc
    6 1.59e-05 -2.74e-06 1.19e-05      2.53 5.56e-05 4.54e-06  5.59e-05 PhantomNPhys Transportation
    7 0.000339 -3.2e-06  1.2e-05      2.52  0.00474 0.000323  0.000379 PhantomNPhys hLowEIoni
    8 0.000626 -3.61e-06 1.19e-05      2.51  0.00401 0.000287  0.000666 PhantomNPhys hLowEIoni 

But the secondary electrons step is inncorrect as following,

*********************************************************************************************************
* G4Track Information:   Particle = e-,   Track ID = 172,   Parent ID = 1
*********************************************************************************************************

Step#    X(mm)    Y(mm)    Z(mm) KinE(MeV)  dE(MeV) StepLeng TrackLeng  NextVolume ProcName
    0    0.101 -0.00038  0.00363  0.000999        0        0         0 PhantomNPhys initStep
    1    0.101 -0.000368  0.00363         0 0.000999   0.0215    0.0215 PhantomNPhys msc
Track (trackID 172, parentID 1) is processed with stopping code 2
### pop requested out of 170 stacked tracks.

I noticed that the StepLeng is always 0.0215 mm. This is obviously outside nanosphere. 
Can you tell me how to setup steplimiter for secondary electrons? (I noticed others
have similar problem)
thank you!
  

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1 None: RE: about step limitation in Hadrontherapy   (Makoto Asai - 11 Mar, 2008)
2 None: Re: about step limitation in Hadrontherapy   (Maria Grazia Pia - 11 Mar, 2008)
1 None: Re: about step limitation in Hadrontherapy   (jfgao@mdanderson.org - 11 Mar, 2008)
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