Brachytherapy in the treatment of thoracic tumors. Lung and esophageal.

For ease of discussion, brachytherapy for carcinoma of the lung will be categorized into interstitial (in tissue) and intraluminal (within a lumen) techniques. Most commonly, in interstitial implantation iodine-125 (I-125) is implanted at the time of surgical resection. Intraluminal treatment is divided into low (LDR), intermediate (MDR), and high dose rate (HDR) applications and refers to the temporary placement of the isotope into the tracheobronchial tree. In the past, radon-222 (Rn-222), gold-198 (Au-198), and iridium-192 (Ir-192) have been used in interstitial brachytherapy. Radon and gold in the form of seeds had been used because of their short half-life and rapid deposition of energy within the target area. Iridium-192 was most often used as individual seed sources in the form of ribbons or strands placed in hollow nylon tubes. However, it was not until the introduction of I-125 with its low-energy gamma emission, primarily in the 30 keV range (27 to 32 keV), and a long half-life of 60 days (precisely, 59.4 days) that the sources could be kept within the hospital and available in a stand-by mode. The newest entry has been the use of palladium 103 (Pd-103) seeds. Like iodine, palladium is a low-energy gamma emitter (23 keV), but with a much shorter half-life of 17 days and thus allows an increased dose rate, which is preferred for treatment of more rapidly growing tumors. Permanent seed implant with I-125 or Pd-103 is best restricted to those patients who undergo surgical resection with margins that are close or positive. In such cases the implantation of seeds provides a high dose to a small volume for local control. There are three primary methods of seed placement. Loose seeds are placed through a hollow stainless-steel needle. The needles are positioned within the target volume in an array, usually with 1-cm spacings, to accomplish a good dose distribution in two planes. The third plane is then set by deposition of seeds at either 5- or 10-mm increments along the needle length. The needles are placed at the maximum depth of deposition, then an applicator is attached to the needles so that the operator can deposit seeds at intervals of 5 mm or more. Thus, the three-dimensional array is first accomplished by placing the needles in a two-plane array and completing the third dimension by slowly withdrawing the needle, and depositing the seeds along the needle track. Obviously, placing hollow stainless-steel needles into vital structures is not possible, so this procedure is used for soft tissues, such as in the chest wall. The needles can also be placed within gelfoam, the seeds deposited, and then the gelfoam placed in a sheet-like manner over an area where implantation might not be possible. To stabilize the friable gelfoam and ensure that the gelfoam and seeds do not migrate, a nonabsorbable (Vicryl) mesh or tissue is needed to cover the implant. The most common implantation technique has been the use of iodine seeds placed within Vicryl suture. Standard Vicryl suture is modified by removing the inner core and placing the seeds, most commonly, at 1-cm spacing, within the resulting space. The Vicryl suture comes attached to a large needle to allow the operator to sew the strand within a specified area. Although the size of the needle precludes its use in most clinical situations, the operator can remove the needle and swag the suture to a needle of appropriate size. Sewing the suture through an area allows excellent spacing and fixation of the seeds. However, more often than not, the nature of the tissues in question (such as the major vascular structures and bronchial margins) prohibits this procedure. In that case, the needle can be removed and the operator can then implant the suture by attaching it to the critical structure with small, weck vascular clips. The vascular clip should always be placed on the suture in between the iodine seeds to avoid crimping a seed. The doses deemed sufficient to eradicate macroscopic disease are 160 Gy for I-125 and 125 Gy for Pd-103. It must be emphasized that this technique requires extensive individual experience and expertise to avoid an excessive complication rate. For example, in a recent intraoperative consultation, the author was asked to perform an implantation on the pulmonary artery of a patient who had undergone a left upper lobectomy with carcinoma stripped off the left pulmonary artery. The author recommended against implantation because there was an extremely high risk of pulmonary artery rupture. One week after surgery, the patient ruptured her left pulmonary artery, and carcinoma was found in the artery wall at autopsy.