Radiology, Vol 146, 791-792, Copyright © 1983 by Radiological Society of North America
Directional dependence of radiation fluence from 192Ir and 198Au sources
CC Ling, ZC Gromadzki, SN Rustgi and JH Cundiff
Radiation fluence distribution around 192Ir and 198Au seeds of the type
used for brachytherapy application was measured using a NaI crystal
connected to a multi-channel analyzer. The radiation fluence, determined as
a function of the angle between the seed axis and the direction of
detection, is anisotropic with the fluence along the seed axis amounting to
78% of that perpendicular to the seed axis for seeds of both isotopes. The
region of fluence reduction is broader for 198Au seeds, extending from 0-45
degrees; for 192Ir the decrease in fluence is evident for angles of 0-20
degrees. Integration of the angular distribution over 4 pi geometry
indicated the effective activity of the implants to be 4% and 1% less than
the nominal activity for the 198Au and 192Ir seeds, respectively, based on
calibration measurements perpendicular to the seed axis.
