From: Alberto Fasso' (fasso@SLAC.Stanford.EDU)
Date: Wed Jan 30 2008 - 02:34:55 CET
There is some confusion in my head about what we call a "Bragg peak".
Please, Florian and other experts, help me clarify this concept.
Does the Bragg peak refer to the local dose along the path of the charged=
=20
particle, or to the laterally integrated dose?
If the dose is laterally integrated, a FLUKA binning is not the correct
technique to determine it (unless, of course, the bins are laterally
"infinite"). If instead the dose is local, the result can be strongly
dependent on the bin lateral size and on the delta ray cutoff.
Is there any accepted convention?
I have done some research on Internet and my confusion has increased.
For Wikipedia, the Bragg peak refers to the "energy loss" (not to the "ener=
gy
deposition"): therefore, the dose seems to be laterally integrated.
For the Encylopaedia Britannica, the Bragg peak refers to ionization. This =
is
less clear: total ionization is laterally integrated, but primary ionizatio=
n is
not. The exact text is:
"The ionization density (number of ions per unit of path length) produced b=
y a=20
fast charged particle along its track increases as the particle slows down.=
It=20
eventually reaches a maximum called the Bragg peak close to the end of its=
=20
trajectory".
It speaks about "The ionization density produced by a fast charged particle=
":
does it include ionization due to secondaries, or only by the fast charged=
=20
particle itself?=20
Because it says "ionization density", I think it refers to the primary only=
,
otherwise it would say just ionization.
The first paper by Bragg himself was also ambiguous:
W.H. Bragg and R. Kleeman, "On the ionization curves of radium", Phil. Ma=
g
1904; S.6:726=C2=AD38
Bragg said:
"...measurements of the ionization produced in air by alpha
particles, at varying distances from a very thin source of
radium salt. The recorded ionization curves brought to light
a fact, which we believe to have been hitherto unobserved. It
is, that the a particle is a more efficient ionizer towards the
extreme end of its course."=20
Was that ionization, or ionization density?
The above text is cited by A. Brown and H. Suit, "The centenary of the
discovery of the Bragg peak", Radiotherapy and Oncology 73 (2004) 265.
In their paper, they mention another parameter affecting the Bragg peak,
namely the beam size: for beams of small size "the progressive scatter with=
=20
depth reduces the Bragg peak and for beams of 1=C2=AD2 mm diameter there is=
a=20
decrease in dose with depth". Clearly, that implies a dose NOT laterally
integrated.
Most other papers I have found don't help to remove the ambiguity, with
two important exceptions:
- N.V. Mokhov and A. Van Ginneken, "Muons versus hadrons for radiotherapy"
Proc. 1999 Particle Accel. Conf., New York 1999
- K. Parodi and T. Bortfeld "A filtering approach based on Gaussian-powerla=
w
convolutions for local PET verification of proton radiotherapy"
In both these papers it is very clearly said "laterally integrated".
I tend to think that the laterally integrated Bragg peak should be the righ=
t=20
choice. But in this case the plots should show energy vs depth, and not dos=
e vs=20
depth (GeV/cm, not Gev/cm3 as in the plot sent by Jamshid Soltani).
Or, if the alternative definition is preferred, I think that the following
parameters should be clearely reported, since they are likely to affect the=
=20
shape of the peak:
- beam size
- binning size
- delta ray cutoff
Alberto
On Tue, 29 Jan 2008, Florian Sommerer wrote:
> Dear Jamshid Soltani,
>
> the problem is again just the statistical fluctuation. Increase the numbe=
r of=20
> primary particles and you will see that this fluctuations will decrease. =
As=20
> the statistics goes with the square root of the number of primaries you h=
ave=20
> to increase the primaries by a factor 4 to bring the peaks of the fluctua=
tion=20
> down by a factor of 2.
>
> Please read also carefully the answer Vasilis posted in reply to your=20
> question from Dec 10th.
>
> Regards,
> Florian Sommerer
>
>
> Jamshid Soltani wrote:
>> Hi FLUKA user,
>>=20
>> I want to draw a curve for interaction of charged particles with water a=
s
>> attach file.the Bragg peak of proton beam isn't smooth and there is "zig
>> zag" form in its Bragg peak.I changed the binning in Z direction and it
>> exist the same problem again.I tried to draw a carve for the interaction
>> of proton beam with Calcium(target) and there is the zig zag form.
>> As you see in the bragg peaks of Boron, oxygen and Iron there is sharp i=
n
>> peak too.
>> can anyone tell me, how can I solve this problem?
>>=20
>> thanks
>> jamshid soltani
--1334196822-1027288155-1201656895=3D:18230--
This archive was generated by hypermail 2.1.6 : Wed Jan 30 2008 - 13:13:37 CET