RE: Medical linear accelerators

From: <Kristian.Ytre-Hauge_at_ift.uib.no>
Date: Fri, 22 Mar 2013 20:36:58 +0100

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,

Kristian

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 Sat Mar 23 2013 - 17:26:50 CET

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