BodyBuilder Phantom Generation Code

BodyBuilder interpolates among the Cristy and Eckerman models to construct a model of any age between 1 year and adult. Any combination of organs may be included in the phantom. The specific models generated are in the form of input files for the MCNP Monte Carlo code.

Interpolation Among Ages

The interpolation is first made on the Cristy and Eckerman coefficients. The interpolated values are then transformed into the equivalent MCNP surface representation. A 2-point linear interpolation method is used.

The continuum of ages does not include the newborn model at age 0. The form of the gall bladder geometry and the composition are slightly different for the newborn than for the other models.

We have checked the range of ages for overlapping organs and other geometry errors using the Sabrina graphics code. No errors have been seen following our debugging. The sharing of common surfaces by various organs permits the model to adjust to different sizes without introducing errors. We have also performed geometry checks with a wide variety of organ combinations.  Nevertheless, from time to time a user encounters lost particles in an MCNP run. In nearly every instance, the MCNP geometry plotter shows an extremely small overlap at the position reported for the lost particle. When such problems are found, we modify the respective cell description(s) and list the change on the errata page on the BodyBuilder web site (www.whiterockscience.com/bodybuilder/errata.html).

The (interpolated) organ volumes tabulated in the Oak Ridge reports are included in the MCNP cell description (VOL= parameter). These volumes are used by MCNP for tally normalization. Many cells are too complicated to permit analytic volume calculations.  The volumes are omitted if a BodyBuilder modification invalidates the report value (such as the leg skin volume in the legs up and sitting cases).

Known Deficiencies

Several of the Oak Ridge organ descriptions use 4th order surfaces; MCNP surfaces are restricted to 2nd order quadrics (except for the torus). An approximate model is used instead of the 4th order thyroid description. For the later models with a distinct neck, we have moved the thyroid rearwards so that it remains inside the neck. The other affected organs are the 6 and 9 month pregnant urinary bladders. These bladders are omitted at present.

Some models may contain duplicate surfaces—two surfaces that are identical. While not a problem for MCNP, these surfaces may cause spurious geometry errors to be displayed when TESTing the geometry in Sabrina. Usually there is no corresponding entry in Sabrina’s geometry error report (errfile.txt).

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Last modified: September, 2004