Afterloading Technic with Rigid Needles Interstitial Radiation Therapy

Abstract

Interstitial radiation therapy is a frequently employed modality for cancer of the head and neck and the breast and chest-wall areas. Standard technics call for preloaded rigid needles containing radium or cobalt 60. Several difficulties, however, are inherent in the use of these preloaded source holders. To overcome these difficulties, at least partially, a technic for loading radiation sources into hollow stainless steel needles after their implantation (afterloading) is now under development. The aim has been fourfold: a. To increase the facility and accuracy of the needle implantation technic. If radiation exposure is eliminated during placement of the needles, unhurried attention may be given to obtaining an excellent source distribution, with repositioning of needles as required. b. To reduce radiation exposure to all persons concerned with patients receiving interstitial therapy, i.e., the radiation therapists, the radium custodian, the operating room, recovery room, and ward nursing staffs, the diagnostic x-ray technical staff, the radiation physicist who calibrates and maintains the inventory of sources. c. To design needles for ease of source insertion, reduction of tissue trauma, and convenience of handling during implantation in the tissue. d. To develop new implant designs, permitted first by an increase in selection of needle lengths and shapes; second by a choice of positioning of the radiation sources along the needle length. Technic Needles: The two needle designs in current use are shown in Figure 1. For intra-oral implants, where loading of posterior needles is difficult, a special needle head is constructed so that there is a funnel leading to the shaft. The needles for chest-wall and neck areas are lengths of stainless steel tubing with a point cut on one end and crimping just above the point. The opposite end is slightly flared to facilitate insertion of the wire. For these simple needles, sutures are not threaded through an eyelet; a ligature is placed just below the head or flared end and is fixed to the steel tubing by a drop of Eastman 910 bonding agent. Radiation Source: Except for the use of cobalt-60 wires in 3 cases, iridium-192 wires have served as the radiation sources. These were generously provided by Dr. Ulrich . Henschke. The iridium is in the form of an iridium-platinum alloy in a filament 0.005 inch in diameter. This filament is fixed in a stainless steel tube with an outside diameter of 0.012 inch. The inside diameter of the steel tubing in the needle is 0.023 inch, thus permitting easy insertion and removal of the sources. Iridium 192 is an artificial radioactive isotope with a half-life of 74.5 days, a mean effective gamma energy of 0.4 Mev (Wilson), and a maximum beta energy of 0.66 Mev (Strominger, et al.). beta particles are effectively shielded by the steel cases.