AbstractID: 7702 Title: Extracranial, CT Guided Utilization of the GliaSite Radiation Therapy System The GliaSite Radiation Therapy System (RTS), is an inflatable balloon catheter that is afterloaded with a liquid I-125 solution (Iotrex) for the treatment of the margins of resected brain tumor cavities. The device is typically placed in a brain tumor resection cavity with the access port subcutaneously secured to the patient’s skull. The device is available in three sizes, 2, 3 and 4 cm diameter balloons with volumes of 5, 15 and 35 ml, respectively. Iotrex and saline are then afterloaded at the patient’s bedside. In this particular instance, application of the device was used extracranially for a patient with recurrent, previously irradiated nasopharynx cancer. A 4 cm catheter was initially placed transnasally. The distal infusion port was sutured to the one of the patient’s nostrils. The balloon was filled with saline and visually inspected for proper placement. Imaging on a CT simulator revealed that the balloon was not conforming to the cavity as desired. The 4 cm balloon was replaced with two 2 cm balloons, refilled and re-imaged. The balloons were positioned to deliver a uniform dose to the nasopharyngeal mucosa. The devices were ultimately filled with a combined activity of 194 mCi and left in place for 39 hours, delivering a dose of 20.6Gy at a depth of 0.5cm. GliaSite RTS device is feasible for treating nasopharyngeal tumors. It is recommended that CT imaging be used for verification of location and fill volume. Research supported in part by Proxima Therapeutics Corporation.