Energy absorption and exposure build-up factors in hydroxyapatite

The effective atomic number (Z(eff)) and electron density (N-el) of hydroxyapatite (HA) and cortical bone have been computed for total photon interaction in the wide energy range of 1 keV-100 GeV using WinXCom. The variations of effective atomic number and electron density with energy of HA are compared with that of cortical bone. GP. fitting method has been used to compute energy absorption and exposure build-up factor of HA for wide energy range (0.015 MeV-15 MeV) up to the penetration depth of 40mean free path. The computed absorption build-up factor is used to estimate specific absorbed fraction of energy (Phi) and relative dose of photon in HA. Build-up factor increases with increase of penetration depth. The results of the present paper will also help in estimating safe dose levels for radiotherapy patients and also will be useful in dosimetry and diagnostics. (C) 2012 Elsevier Ltd. All rights reserved.