Re: Medical linear accelerators

From: Moskvin, Vadim P <vmoskvin_at_iupui.edu>
Date: Tue, 5 Mar 2013 15:17:26 +0000

Dear Kristian,

Normalization factor depends on the size of an electron beam impinging on a target, a way how it was simulated (Gaussian or flat). The reference conditions may impact too, I.e. SSD of 90 or 100 cm. Perhaps yours was 90 cm as recommended, just to double check.

Best Regards,

Vadim

Sent from my iPhone

On Mar 5, 2013, at 8:55 AM, "Kristian Ytre-Hauge" <kristian.ytre-hauge_at_ift.uib.no<mailto:kristian.ytre-hauge_at_ift.uib.no>> wrote:

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 settings):

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.

Thanks,
Kristian Ytre-Hauge
Received on Tue Mar 05 2013 - 17:51:41 CET