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From: Kristian Ytre-Hauge <kristian.ytre-hauge_at_ift.uib.no>
Date: Fri, 5 Apr 2013 14:47:04 +0200

In-Reply-To: <60E29B00B1D83B408187D55F5E941115C22F95DC_at_CERNXCHG21.cern.ch>
Subject: RE: Medical linear accelerators
Date: Fri, 5 Apr 2013 13:22:03 +0200
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Dear Anton,

Thank you for your reply.

It is correct as you say that we have normalized to different depths.

The reason why you do not find the value I reported (2.72E15) in the paper
is that I recalculated the original value (at Dmax)to the corresponding
value at 10 cm depth to enable a more realistic comparison of the
simulations. (Based on the depth dose curve of 15 MV photons the ratio of
dose at Dmax and 10 cm depth per electron can be found.) This is of course
only an approximation, and one must be aware that there are other
differences such as the SSD (source-surface distance) which is 90 cm in my
case and usually 100 cm when using Dmax calibration.

You might be right that the differences mainly are from geometrical
differences, but it is difficult to say.

Thank you also for confirming that the physics settings are reasonable.


-----Original Message-----
From: Anton Lechner [mailto:Anton.Lechner_at_cern.ch]
Sent: 5. april 2013 11:41
To: Kristian Ytre-Hauge
Cc: fluka-discuss_at_fluka.org
Subject: RE: Medical linear accelerators

Dear Kristian,

Your physics settings for calculating the photon-induced dose (PRECISIO +
production cuts of 10 keV for electrons and photons) appear to be
appropriate for this study (i.e. Bremsstrahlung photons produced by 15 MeV

As already mentioned, without direct comparison of geometric aspects it is
hard to say where the discrepancies originate from. I had a look at one of
the papers you mentioned (Martinez-Ovalle et. al.) and I can only find a
value of 2.04E15 electrons/Gy (for the Varian Clinac with 15 MeV) and not
the 2.72E15 electrons/Gy you wrote in your initial Email. In addition, you
mentioned you calculated the dose value at 10 cm depth in water, while
Martinez-Ovalle et. al. say that their value is based on the maximum of the
depth dose profile (which is at a more shallow depth). Might it be that the
discrepancies are (partially) explained by this? Also, looking at the
different results Martinez-Ovalle et. al. got for different Linacs (apart
from differences in energy) one could imagine that geometric discrepancies
can matter lot.

Cheers, Anton

From: Kristian.Ytre-Hauge_at_ift.uib.no [Kristian.Ytre-Hauge_at_ift.uib.no]
Sent: 22 March 2013 20:36
To: Anton Lechner
Cc: fluka-discuss_at_fluka.org
Subject: RE: Medical linear accelerators

Dear Anton,

Thank you for you answer.

I apologize for the late reply, but now I have attached a simplified input
file with an example of the settings I have used for production thresholds,
scoring and more.

For the scoring at the isocenter I have typically used a sphere of radius of
1 or 2 cm.

Thank you again for the help,


Quoting Anton Lechner <Anton.Lechner_at_cern.ch>:

> Dear Kristian,
> Without knowing the different treatment head geometries and other
> geometrical factors (e.g. beam size, scoring) it is hard to judge
> where the differences arise from. My feeling is that if geometries,
> beam and scoring would exactly match, then I would expect results in
> better agreement than factor of 5 (as you get for MCNPX/FLUKA).
> What electron energy are you considering and what transport thresholds
> are you using? In any case, I would use PRECISIO for the DEFAULT
> setting. And how big is the scoring volume you look at? Even if you
> cannot send the geometry, maybe you could send me your physics and
> scoring cards such that I can have a look.
> Cheers, Anton
> ________________________________________
> From: Kristian.Ytre-Hauge_at_ift.uib.no [Kristian.Ytre-Hauge_at_ift.uib.no]
> Sent: 06 March 2013 09:52
> To: Moskvin, Vadim P
> Cc: Kristian Ytre-Hauge; fluka-discuss_at_fluka.org
> Subject: Re: Medical linear accelerators
> 2013 09:52:20 +0100 (CET)
> X-Virus-Scanned: clamav-milter 0.97.6 at smtp1.mi.infn.it
> X-Virus-Status: Clean
> Sender: owner-fluka-discuss_at_mi.infn.it
> Dear Vadim,
> Thank you for you email.
> I agree that there are many variable that may have an impact.
> The SSD of 90 or 100 cm and changes in material density (especially
> the flattening filter) seems to give changes up to about 10%. While
> the differences in the literature are up to a factor 5.
> The size of the electron beam is typically 1 mm FWHM or a bit bigger.
> I have not investigated in detail the impact of this parameter with
> respect to the number of primary electrons needed per Gy, but I
> suspect that the impact of this parameter is relatively small compared
> to the observed discrepancies?
> Thanks again,
> Kristian
> Siterer
>> 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 Fri Apr 05 2013 - 15:24:50 CEST

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