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Eurados exercise on uncertainty assessment in micro- and
nanodosimetry using Monte Carlo calculations
1. Objective of the exercise
The exercise proposed by the task 2 of the Eurados WG6 (Computational Dosimetry), is
defined with two different objectives. On one hand, different Monte Carlo codes using
different cross-sections data tables or models will be benchmarked in terms of
microdosimetric results obtained in a liquid water target that is often used as biological
material.
On the other hand, some Monte Carlo codes also provide capabilities to perform
nanodosimetric calculations that will be also benchmarked in this exercise. The exercise has
been conceived in a way that, the differences in the nanodosimetric results should be mainly
due to differences in the cross-sections used by the codes. Therefore, these differences in
the results will be quantified and analyzed to be used as an uncertainty budget applied to
the cross-sections in a future exercise in which different codes will use the same set of crosssections.
This exercise is open to any participant. Each person sending results should clearly specify
which MC code was used and which was the energy cut for the production and
transportation of the electrons.
The analysis of the received results will be made by the core members of the T6.2 and a
summary report ensuring anonymity will be written by the end of 2016. We encourage
participants to use different MC codes with different cross-sections sets to obtain a good
estimation of the uncertainty budget that can be obtained nowadays in the frame of
computational micro and nanodosimetry.
Exercise description
a. Source description:
A radioactive 125I source is placed within a liquid water sphere with 10 µm diameter (Fig. 1).
The electron spectrum which is part of the decay process is taken from Howell et al., Med.
Phys. 19 (6) 1992. In this spectrum, we will only simulate one decay as 24.9 (25) Auger and
CK electrons + 0.94 (1) IC electron as shown here after. The additionally produced lowenergy x-rays are not considered as their interaction probability within the micrometric
target is negligible.
b. Microdosimetric calculations:
Three source distributions are considered (with the initial activity A0):
1. Point source in center of the sphere: ρ(r) α A0 (r)·δ(r)
𝐴
2. Volume homogeneous distribution within sphere: 𝜌(𝑟) = 𝑉0 Θ(𝑟0 − 𝑟), with the
sphere's radius r0 and its volume V (results sensitive to energy cut of electron
transport)
𝐴
3. On the surface of the sphere: 𝜌(𝑟) = 𝐴0 δ(𝑟0 − 𝑟), with the sphere's radius r0 and its
surface A
R=5 µm
1. Point Source
R=5 µm
R=5 µm
2. Volume source
3. Surface source
- For the three configurations, calculate the specific energy distribution f(z) (Gy) per
disintegration and plot the specific energy histogram : zf(z) vs z in Gy.
- Calculate the total absorption spectrum
n
For the histograms, use logarithmic scale on the f(z) axis with min ∗ 10β and β=100
c. Nanodosimetric calculations
The same liquid water sphere of 10 µm diameter used in the microdosimetric exercise is
used here with the point source of 125I. This time the targets are placed within the 10 µm
diameter sphere. The targets are small spheres of diameters 3 nm (similar to the DNA
double helix size) and 8 nm diameter (similar to the nucleosome size). They are located at
0, 1, 2, 4 and 8 times their radius from the point source. The following quantities shall be
calculated for each decay:


Deposited energy histogram
Number of ionizations (ionization cluster size distribution normalized to 1):
125
I Source
Target 1 diameter: 3 nm
(liquid water)
Target 2 diameter : 8 nm
(liquid water)
Distances from the source: 0,
1, 2, 4 and 8 times the target
radius
D: 10 µm
2. Results
Please, send your results to Carmen Villagrasa at: [email protected]
Specify:
-
which MC code was used
the energy cut used for the creation and transportation of electrons
Dead line for sending your results is 30/6/2016
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