Measurement and Estimation of Organ Bremsstrahlung Radiation Dose

Bremsstrahlung radiation doses were measured in an anthropomorphic phantom using thermoluminescent dosimeters. A single source of 90Y (beta-ray range less than or equal to 1.0 cm) was inserted in the bladder region and dosimeters were placed at distances greater than or equal to 3 cm to preclude detection of decay betas. Doses were corrected so as to represent the case of no biologic clearance. By comparing dosimeter location with the standard MIRD human geometry, sample organ doses could be determined. Representative results were 432 +/- 76 mrad/mCi at 3 cm (bladder), 260 +/- 60 mrad/mCi (uterus), 71 +/- 4 mrad/mCi (lower large intestine), and 1.4 +/- 0.7 mrad/mCi (liver). An estimation method, based on absorbed fraction tables, gave organ doses that were within the errors of measurement for all tissues with the exception of the bladder site. We conclude that organ bremsstrahlung radiation doses are not negligible and that they can be estimated using an integration over both the brake and beta-ray spectra.