Design and characterization of a rigid interstitial implantation device using iridium-192 seeds

We describe a simple, inexpensive applicator for rigid interstitial implantation using iridium-192 seeds. Implantation of the oral tongue using ¹⁹²Ir seeds is usually accomplished using flexible plastic catheters with a combined intraoral and submental approach. The dosimetric characteristics of such a procedure can sometimes be imperfect due to the undesirable curvature of the flexible plastic tubes. We designed a device using rigid, stainless-steel needles preloaded with ¹⁹²Ir in an attempt to deliver a more homogeneous dose. Needle of 4.5-cm length, with a taper tip and of 18- gauge diameter were placed into a custom-designed nylon bar at 1-cm spacing. The bar held four needles in a rigid parallel configuration and included a fifth crossing needle of 3 cm in length. Device construction required a new weeks' notice and approximately $150. A description of the device is provided, along with the clinical results of a patient treated with the device. Dosimetric analysis is presented. This article describes a simple, practical, and inexpensive method for constructing a customized brachytherapy device that has the dosimetric and clinical advantage of rigid interstitial needles, which may be used by departments unable to stock cesium-137 needles.