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.

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The computerised treatment planning algorithm used at the University of Chicago Neutron Therapy Facility is based on linear interpolation of experimental beam data. These were obtained by relative ionisation measurements with a TE chamber in TE solution contained in a large square phantom with the beam incident normally onto a flat surface. Under these conditions, the d(50%) for a beam 12 x 12 cm2 at 105 cm from the target is 10.2 g.cm-2. In the dose calculation algorithm, surface curvature is taken into account by using the ratio of TPRs for the density weighted path lengths for the oblique and central rays. The purpose of this work is to test this calculation approximation by comparing measurements and calculations in a cylindrical, water-filled phantom with variable curvature cross section. Results of measurements and calculations are presented for two beam geometries.

We have investigated the performance characteristics of PIN diodes as neutron dosemeters. Data were obtained on dose response as a function of accumulated dose and neutron beam quality. We have studied fading characteristics at room temperature and developed a technique for partially annealing the radiation damage. After two years of experience with PIN diodes we tested them for their usefulness as mail dosemeters among the six neutron therapy facilites in the United States. Our results show that intercomparison of calibrated neutron beams is achievable with a precision of ±3%.