Radiotherapy of the resected mandible following stainless steel plate fixation.

There is general concern among otolaryngologists that irradiation of a stainless steel prosthesis used in mandibular reconstruction may cause irradiation overdosage to adjacent tissues. A tissue-equivalent plastic/steel model, simulating the characteristics of a stainless steel, reconstructed mandible, was irradiated and measurements were made with a parallel plate ionization chamber. The results of our measurements show that irradiation of an implanted steel plate results in an overdosage (120%) "in front" and an underdosage (80%) "behind" the steel plate. The regions of overdosage and underdosage are 2 to 3 mm thick. The overall dose modification is greatly reduced when two opposing fields are used. We conclude that irradiation of a stainless steel, reconstructed mandible with a 6-mV photon beam through opposing fields does not significantly alter the amount of radiation delivered to surrounding tissues.