3-D reconstruction of Ir-192 implant dosimetry for irradiating gingival carcinoma on the mandibular alveolar ridge.

A recurrent cancer in the gingiva has been treated by specially fabricating a dental acrylic appliance. This replica of the floor of the mouth, gums, and teeth was constructed with the use of a vinyl polysiloxine impression material. The tumor boundaries were marked in the fabricated appliance with four metal wires to localize the surface and periphery of the tumor. The appliance was molded to hold Ir-192 wires in near contact with the target surface and to allow afterloading. A specially designed lead shield was imbedded onto the dorsal surface of the appliance so as to reduce dose to the tongue and maxillary structures of the mouth. Simulation films and 3-D treatment planning were used to generate isodose distributions and to allow preplanning. The dose calculation algorithm was modified to account for the attenuation in the lead shield represented in three dimensions. The Ir-192 mold was successfully applied for 38 hours in two sessions 1 week apart.