Re: Delta-ray production threshold

From: Alfredo Ferrari <alfredo.ferrari_at_cern.ch>
Date: Tue, 25 Sep 2012 10:10:00 +0200

Dear all

the reason is not lack os statistics. The reason is that Jean-Emmanuel
broke artificially electronic equilibrium by using a different (lower)
threshold in the cell culture part wrt the materials before and after,
which is a major conceptual mistake. Obviously the lower the delta
threshold in the culture region wrt the surrounding the larger the amount
of low energy electrons produced there close to the interface which escape
into the surrodundings without being "compensated" by those produced in
the surrounding because of the (wrongly) higher threshold -> a fake
reduction in dose. The correct way is to set delta thresholds (and
electron transport threshold) equal and correspodning to a range of say
1/4-1/10 of the cell culture thickness, if this is too cpu expensive for
the surrounding region, they can be split into two pieces keeping the
threshold the same only in the layer directly in contact with the cell
culture.

                 Alfredo

+----------------------------------------------------------------------+
| Alfredo Ferrari || Tel.: +41.22.76.76119 |
| CERN-EN/STI || Fax.: +41.22.76.69474 |
| 1211 Geneva 23 || e-mail: Alfredo.Ferrari_at_cern.ch |
| Switzerland || |
+----------------------------------------------------------------------+

On Sun, 23 Sep 2012, tkatsh65_at_mail.ru wrote:

>
> Jean-Emmanuel,
>
> Â
>
> I think the reason is lack of counting statistic in cell culture region
>
> because its volume less about 10 times than cover slip and water volumes.
>
> So ranging from 0.18 cGy to 0.2 cGy is statistic fluctuation.
>
> Â
>
> Best regards,
>
> Â
>
> Oleg
>
>
>
>
> Thu, 13 Sep 2012 17:40:31 +0200 от Jean-Emmanuel Groetz
> <jegroetz_at_univ-fcomte.fr>:
> Users and experts,
>
> With FLUKA, I have calculated the dose deposited by iron ions at
> 1 GeV
> and secondaries (electrons, photons, protons...) in a cell
> culture with
> 1 micron thick (between a cover slip and water).
> I used the HADROTHErapy option, with a transport cutoff at 1 keV
> for all
> particles and 150 eV for electrons (as Alfredo Ferrari suggested
> in a
> paper PMB 56 - 2011).
> When I modified the delta-ray production threshold (only in the
> cell
> culture) from 1 keV to 10 and 100 keV, the dose deposited by
> heavy ions
> increased and the dose from electrons decreased, as expected.
> But if I
> consider the total dose in the cell culture, it is not constant,
> ranging
> from 0.18 cGy to 0.2 cGy (the experimental dose was about 0.2
> cGy).
> Total doses in cover slip (1 mm thick) and in water (1.9 cm)
> remain
> constant.
>
> I am wondering what could be the reason of such results in the
> cell
> culture.
>
> Thank you in advance for your help and suggestions.
>
> Jean-Emmanuel
> --
Received on Wed Sep 26 2012 - 10:21:26 CEST

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