Hi everyone

Hi everyone,

I have a pretty fundamental question regarding parallel runs in EGSnrc. I’m finding that the individual pieces of a parallel run do not necessarily agree with each other within their stated uncertainties, even in a very simple simulation.

More fundamentally, I’m seeing “large” discrepancies between two basically identical simulations that were both run in a parallel environment and combined. The reported cavity doses do not agree within the stated simulation uncertainties.

For a very simple example, I made a 1 cm radius Virtual Water cylinder that is 6 cm long as my dose scoring object. I enveloped that rod inside a 10 cm cube of water. The source was a collimated point source of 6 MV photons above the rod but still inside the water box. The dose to the entire rod was scored by running 5e10 histories total. No VR was implemented.

The simulation was run on a parallel cluster that contained 72 CPUs so the job was split into ~5e10/72 histories per CPU. In the plot I included, it’s straightforward to see that the results of the individual jobs (which should ostensibly be identical right?) do not always agree with each other within their stated uncertainty. Considering that each job ran almost 7 million histories, I don’t think this is just an undersampling issue.

Given that the final result of the combined jobs is the average dose/SP to the cavity, is this to be expected? Why wouldn’t the results converge more tightly towards a given answer?

When I instead brute force the same simulations in Windows without using parallel CPU computing, I get results that do ostensibly agree within their stated uncertainty but I need to run more simulations to definitively show that this is always the case.

Since I’m personally running IMRT modulated phase spaces into small geometries in egs_chamber on a cluster, these small fluctuations in the cavity dose results have me pretty alarmed since the prescribed corrections are often on the order of <1%. Any tips to help me better understand the nature of uncertainties in parallel computing would be awesome, especially why this happens even in a very simple usage scenario like the one I described. Thanks!

Hi all

Hi all,

I have finished the Beam part ( I have an egsphsp1 files with the CM configuration)

My egsphant file is also ready.

I have run the DOSXYZnrc program with

– egsinp file ( with 2 links ; one with the link of .egsphsp1 and the other for egsphant)

When I want to verify if I have photons in the 3ddose file, I get only zero or low values in the egsdat.

I have two quetions :

– Is that a normal situation ?

If not, how can I fix the problem ? (changing my beam ? ; modify my egsphant file ?)

– Am I looking in the right file ?

Best regards,

Emeric

Hi all

Hi all,

I am currently trying to get a good egsphant.

I have different issues depending on the materiel_ct lower bound : – 512 / -1024

Issues with -512 :

I have three medias instead of two : 0.1.2

The 1 and 2 seems to be the same material as we have the epid area fullfilled of 1 instead of 2.

Have you ever seen this ?

Issues with – 1024 :

We do not have th EPID area at the bottom of the phantom.

Do you know why ?

You will find enclosed the phantom for -512 : -1024 and a parameter file.

The 1024 might be the best I think.

Best regards,

Emeric

Hi everybody

Hi everybody,

I have an issue with my phantom preparation. When I run my CT_create.inp file, I get a *.egsphant which is full of 1. I should have a *.egsphant file with a water block shape. (made with 1 and 2 because I have 2 media). My CT input is a folder (dim: 512.117.117) with 117 CT slices.

I don’t know where does the problem come from, I assume it is a dimension problem…

Thanks for your help!

hi

hi

i was trying to run and geometry wth the following code

:start geometry definition:

# The base geometry, this will be the Chopping Device (CD)

# The base geometry can be any geometry, even a composite one

:start geometry:

name = my_cd_planes

library = egs_planes

type = EGS_Zplanes

positions = -3 3 5

# No media required

:stop geometry:

:start geometry:

name = my

library = egs_box

box size = 0.2 0.07 1

:start media input:

media = water

:stop media input:

:stop geometry:

:start geometry:

name = my_box

library = egs_box

box size = 0.45 0.09 1

:start media input:

media = water

:stop media input:

:stop geometry:

:start geometry:

name = g1

library = egs_box

box size = 0.36 0.065 1

:start media input:

media = iron

:stop media input:

:stop geometry:

:start geometry:

name = my_c

library = egs_envelope

base geometry = my_box

# Inscribed geometries must be strictly inside the envelope

# No touching of surfaces!

inscribed geometries = g1 my_box

:stop geometry:

:stop geometry:

# The composite geometry

:start geometry:

name = my_cd

library = egs_cdgeometry

base geometry = my

# set geometry = 1 geom means:

# “in region 1 of the basegeometry, use geometry “geom”

set geometry = 0 my_cd_cylinder

set geometry = 1 my_c

# The final region numbers are attributed by the cd geometry object;

# Use the viewer to determine region numbers

:stop geometry:

simulation geometry = my_cd

:stop geometry definition:

but this error occured

Hi all

Hi all,

I would like to calculate the energy spectrum (i.e. option 3 in BEAMDP for planes) in different volumes. If I’ve understood correctly, cavity code would have option to do this – right? Is cavity code only user code suitable for calculating the spectrum in volumes, such as:

– water cylinders (inscribed into water phantom)

– air cylinder (inscribed into water phantom)

and

– air volume in detailed detector geometry (inscribed into water phantom).

If cavity is the only code, how do I select which particles to include (i.e., photons only, photons + electrons, electrons + positrons, photons + electrons + positrons etc.).

Thank you for your help!

Br,

Mari

Dear EGSnrc expert

Dear EGSnrc expert

I have just simulated two parallel opposite lung field using BEAMnrc/DOSXYZnrc code. But i have a doubt about matching the field size of simulation with TPS ( see the attached files, left : TPS, right: Monte carlo).

can anyone help me about this problem?

please help me

any help would be much appreciated