Medical linear accelerators

From: Kristian Ytre-Hauge <>
Date: Tue, 5 Mar 2013 14:16:50 +0100

Dear Fluka experts,

I am simulating the neutron fluence and dose from a medical linear
accelerator for radiation therapy.

The principle of these accelerators are that an electron beam produces a
wide photon field when hitting a target (typically Tungsten/copper target).

In the first step of my simulation I am trying to establish the photon dose
per primary electron under reference conditions,

where reference condition means: dose in a small volume at 10 cm depth in
water from a 10 x 10 cm2 photon field ++.

When comparing my results to studies with other MC codes in the literature
there are clearly large differences (for the same accelerator model and same

My work (FLUKA): 5.44 e14 primary
electrons per Gy [e-/Gy]

Martinez-Ovalle et. al. (MCNPX, 2011): 2.72 e15 [e-/Gy]

M.K. Saeed et. al. (Geant4, 2009): 1.25 e15 [e-/Gy]

Because the neutron doses are reported per primary particle, the factors
above are of great importance when we wish to report e.g. the neutron dose
per treatment Gray.

Does anyone have any suggestions on which parameters that may cause such
large differences, or if differences of this magnitude is expected when
using different Monte Carlo codes?

My statistical error is 0.1% and no biasing has been used.

I have used both the EM-CASCADE and PRECISION defaults (with similar
results) and photonuclear reactions have not been activated when studying
the photon dose.

Due to confidentiality agreements with the vendor I am prevented to upload
my Geometry.

Any comments are welcome.


Kristian Ytre-Hauge
Received on Tue Mar 05 2013 - 15:14:33 CET

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