2. Outline Intro: voxel phantom + MCNPX Building geometry
Source sampling (ext, int)
Scoring (average, distribution)
Examples: Klara, Godwin
Summary

3. Voxel Phantom Anatomical Realism before now
Millions of boxes assigned to different organs and media

4. MCNPX Monte Carlo general purpose code
MCNP-4C3 + LAHET + Fluka89 + CEM2k + ...
34 particles
Mix-and-match (tables vs models)
Fast lattice initialization new
Fast scoring in lattice new
And more…

5. Voxel Phantom Specification
Voxel dimensions X-Y-Z
3D array of organ IDs ~ 10 MB in binary
Organ ID => Material
Material definitions elements, density

6. MCNPX Repetitive Geometry
Traditional cells/tallies: 10e6?
Repeated Structures
voxel
3D lattice

7. STEP 1: Constructing 3D Lattice
Define voxel surfaces
Define lattice
1 rpp
Block 2 x y z
lat=1 u=999 & fill=0:254 0:131 0:219 &
Block 1 x y z
Indices:
Followed by array of universes (organ IDs)

8. STEP 2: Defining Basic Universes
Universe = Organ
Define a list of universes u= 1 $ universe # u= 5 $ universe #5
Block 1
Mapping:
mat + rho => universe
Plane
7 pz -1000e2
Block 2

9. STEP 3 Filling Phantom Box with Lattice
Define surfaces of phantom box 2 rpp
Fill the phantom box cell with lattice
fill=999
Block 2 x y z
Block 1

10. Miscellaneous Geometry plot!
Compressor of voxel data bin 12 MB => ASCII 3 MB
READ card + NOECHO option read phantom.geom noecho read phantom.mat noecho
Suppress huge tables in production runs print saves RAM

11. Source Sampling
External Source sdef par=p erg=3 sur=2.1 x=51 y=d2 z=d3 vec= dir=1 si $ samples Y from 0 to 26.7 cm sp $ samples Y uniformly si $ samples Z from 0 to 176 cm sp $ uniformly
Internal Source (efficiency!) sdef par=p erg=0.1 cel=d5 x=d1 y=d2 z=d3 eff=1e-4 si5 L (11<999<100) $ all voxels of uni 11 in lat 999 in cell 100 sp $ uniform sampling # si1 sp1 si2 sp2 si3 sp3 $ three distr-s for coord-s sampling $ coord-s start at low voxel border

12. MCNPX Scoring in Lattice
Recent versions speedup for scoring in lattice by orders of magnitude in full mesh!
Unified syntax (source sampling and scoring) *f18:p,e (1<999<100) $ id=1 Adipose tissue, head
Newest version 2.5.0: F8 tallies in all voxels *f8:p,e (999<999[0:254 0:131 0:219]<100) talnp $ tally no print prdmp 2j 1 $ get data via MCTAL file

13. Adjusted Voxel Phantoms: Klara, Godwin
Based on CT data: woman and man
Adjusted to ICRP 89 Reference Man (V, m, h)

14. Godwin (2.085 × 2.085 × 8) mm 255 × 132 × 220 7.4e6 voxels
2e6 non-void
85 organs

15. GOdwin LLAT

16. mcplib02
Fixed XS

18. 1 source photon
No transport: NOTRN
Time = 14 min

19. 1-MeV Neutron Beam
TECplot
MCNPX plot

20. Summary Geometry objects used Fast initialization: < 1 min
Acceptable speed: 1-2 h per 10e6 src photons
RAM used: 500 MB (scoring, tables!)
Good agreement with EGSnrc
Get fresh version of MCNPX
MCNP-5