Help Needed with MCNP Simulation for Brachytherapy Treatment Room

[GeneDeitch]

TL;DR

MCNP;Brachytherapy

Hello everyone,

I am currently working on a Monte Carlo N-Particle (MCNP) simulation and have encountered several issues that I hope someone here can help me resolve. My project involves simulating a brachytherapy treatment room, and I am struggling with defining the cells, surfaces, and materials correctly. Here are the details of my setup:

1. Room Dimensions: The treatment room is designed with 75 cm thick concrete walls on all sides. Additionally, there is a 5 cm thick steel shielding within the room.
2. Door Construction: The entrance door is composed of 3 cm of wood and 2 cm of plastic.
3. Environmental Conditions: The entire room is filled with air.
4. Water Phantom: There is a water phantom simulating a person, with dimensions of 178 cm x 70 cm x 25 cm. The radioisotope source is placed at the height of the esophagus, approximately.

Despite several attempts to accurately define the geometry and materials in MCNP, I continue to receive errors such as "plot plane coincident with surface" and other surface-related errors.

Here is the current definition of my materials:

c =========================================================================
c       Materials
c =========================================================================
m1    1001  0.10
      6000  0.18
      7014  0.03
      8016  0.65
      11023 0.0015
      12000 0.0005
      15031 0.01
      16000 0.0025
      17035 0.0015
      19039 0.0035
      20000 0.015
c Water phantom (simulating a person)
m2    1001  0.011
      8016  0.519
      11023 0.001
      13027 0.019
      14000 0.328
      20000 0.101
      26000 0.021
c Concrete walls
m3    6000  0.00030
      14000 0.0020
      25055 0.0006
      26000 0.7298
      28000 0.0900
      24000 0.1800
      42000 0.00030
c Steel shielding
m4    1001  0.059
      6000  0.492
      7014  0.001
      8016  0.414
      16000 0.001
      19039 0.001
      20000 0.002
      12000 0.030
c Wood door
m5    1001  0.14
      6000  0.86
c Plastic door
m6    7014  0.7808
      8016  0.2095
      18000 0.0093
      6000  0.00012
c Air
Here are the definitions for the surfaces and cells:
c =========================================================================
c       Surfaces
c =========================================================================
1    px    0     $ Surface x = 0
2    px  300     $ Surface x = 300
3    py    0     $ Surface y = 0
4    py  400     $ Surface y = 400
5    pz    0     $ Surface z = 0
6    pz  250     $ Surface z = 250
7    px   75     $ Surface x = 75
8    py   75     $ Surface y = 75
9    py  325     $ Surface y = 325
10   px  225     $ Surface x = 225
c
c Steel shielding (5 cm)
11   px   80     $ Surface x = 80
12   py   80     $ Surface y = 80
13   py  320     $ Surface y = 320
14   px  220     $ Surface x = 220
15   pz  255     $ Surface z = 255
c
c Water phantom (178 cm x 70 cm x 25 cm)
16   px  150     $ Surface x = 150
17   px  328     $ Surface x = 328
18   py  200     $ Surface y = 200
19   py  270     $ Surface y = 270
20   pz   25     $ Surface z = 25
c
c Door construction (5 cm total: 3 cm wood + 2 cm plastic)
21   px   72     $ Surface x = 72 (wood)
22   px   75     $ Surface x = 75 (entire door)
23   px   77     $ Surface x = 77 (plastic)
24   py    5     $ Surface y = 5
25   py   80     $ Surface y = 80
c
c =========================================================================
c       Cells
c =========================================================================
2   2 -2.3  -1 2 -3 4 -5 6 imp:p=1            $ Concrete walls (75 cm)
3   3 -7.86 -11 12 -13 14 -5 6 imp:p=1        $ Steel shielding (5 cm)
4   1 -1.0  -16 17 -18 19 -20 imp:p=1         $ Water phantom (simulating a person)
5   4 -0.64 -21 22 -24 25 imp:p=1             $ Wood door (3 cm)
6   5 -1.406 -22 23 -24 25 imp:p=1            $ Plastic door (2 cm)
7   6 -0.0012 -7 2 -3 4 -5 6 #2 #3 #4 #5 imp:p=1 $ Air in the room
999 0      #2 #3 #4 #5 #6 imp:p=0                       $ Rest of the universe (vacuum)

Any guidance on how to resolve these issues would be greatly appreciated. If you need more details or specifics, please let me know.

Thank you in advance for your help!

Best regards

 

[Alex A]

Hi @GeneDeitch , welcome to Physics Forums,

If 1 is a surface in a cell defnition "1" tends to mean above or, if a shape, outside surface 1. "-1" tends to mean below or inside surface "1".

2   2 -2.3  -1 2 -3 4 -5 6 imp:p=1

1 is px 0, 2 is px 300
So the shape is a volume that is below x=0 and above x=300 and it does not exist. So you have some or all of your cell definitions backwards. Do also correct the void definition to add cell 7.

Simple mistake but a lot of checking needed Good luck!