Comparative dosimetry between iridium wires and seed ribbons.

We have undertaken a computer study that explores the conditions under which seed ribbons may replace iridium 192 wires in the Paris System. Compared with continuous iridium 192 wires, seed ribbons demonstrate greater inhomogeneity and loss of flexibility, simplicity, and other advantages. Nonetheless, we have defined the conditions where seed ribbons may be used in the Paris System to give satisfactory dose distributions and acceptable levels of heterogeneity within any given implant volume. These conditions include seed length, spacing between seeds, number of seeds per ribbon, and geometric arrangement of ribbons.