A NEW CAPACITIVE HEATING APPLICATOR FOR THE SIMULTANEOUS RADIOHYPERTHERMOTHERAPY OF SUPERFICIAL AND SHALLOW-SEATED TUMORS

External capacitive heating is the usual method of electromagnetic wav e heating, in which the tumor is caught and heated between two opposit e applicators. Using a phantom, the authors developed and evaluated th e performance of a new capacitive heating applicator designed for simu ltaneous radiohyperthermotherapy (SRH) in which the electron beam irra diation is provided from above an external capacitive heating applicat or for the treatment of superficial and shallow-seated tumors. The tri al applicator was constructed to fulfill the following conditions: 1. use of an electrode plate which does not affect the electron beam dept h dose, 2. a uniform thickness to maintain flatness of the electron be am, and 3. a cooling function to prevent damage to normal skin tissue and enhance the therapeutic gain factor. This applicator was comprised of a 0.1-mm-thick copper electrode and a 5-mm-thick cooling chamber. The depth of the 80 % dose of the new applicator was 21 mm with a 9-Me V electron beam and 36 mm with a 15-MeV electron beam, which was compa rable to the effect of a conventional irradiation bolus. The temperatu re distribution produced by the trial applicator was symmetrical on bo th sides from the center of the applicator. The 50 % specific absorpti on rate region was 6.4 cm wide at a depth of 1 cm from the phantom sur face and 2.8 cm wide at a depth of 3 cm. There have been no previous r eports on the development of an external capacitive heating applicator designed for the SRH of superficial and shallow-seated tumors; this i s the first such report. SRH of these tumors can be performed simply, noninvasively and repeatedly by means of this new applicator.