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➢
Probability distributions are in the form of a
cross section data base
.
➢
Total partial and differential photon cross sections are required including atomic form
factors F(x, Z) and incoherent scatter factors S(x, Z)
➢
These cross sections must be: complete (in terms of E, Z) self-consistent and up to
date/accurate.
➢
Self-consistency is also required with mass energy absorption data used for kerma
calculation from energy fluence
➢
Up to date cross sections are used in all current versions of benchmarked MC codes:
EPDL97 (LLNL) in the ENDL or ENDF/B-VI formats or the DLC-146 format (ORNL) or
XCOM (NIST) database. Mass energy-absorption coefficients for water by Seltzer and
Hubbell (available on line at NIST).
Data readily available online through NIST
( http://www.nist.gov/pml/data/xraycoef/ )➢
TG-138 (AAPM/ESTRO) cites ~1% cross section type B that contributes to dosimetric
uncertainty at r=5 cm about 0.76 % (low E) and 0.12% (high E)
Type B uncertainty … cross sections