Design of a cylindrical brachytherapy implant applicator for the irradiation of an intestinal segment in mice

Experimental determination of the RBE of new isotopes for brachytherapy implants (e.g. iodine-125 and palladium-103) remains a very difficult problem, especially in small animals, where the seeds cannot be implanted easily in the planned geometry in a reproducible way. This technical note describes an original device that makes it possible to irradiate a segment of the intestine in mice for the purpose of determining the RBE for crypt regeneration. The device is a length of tube (3.4 mm and 7 mm internal and external diameter, respectively) whose external surface has been longitudinally grooved and into which the seeds can be squeezed (each groove holds either one or two seeds). The tube is composed of two sections. This seed container can be surgically positioned around an intestinal ansa while the mice are anesthetized. The mean dose rates in the intestine (for eight seeds) were found to be 86.3 +/- 5.9 and 79.0 +/- 5.4 cGy/h for 29.2 MBq (1 U) iodine and 28.6 MBq (1 U) palladium seeds, respectively. So far, more than 100 mice have been irradiated successfully. Full dose-effect relationships can be obtained using the same seeds and applying them successively in different groups of animals (which ensured the accuracy of the relative doses). (C) 2003 by Radiation Research Society