Development of a Capacitive Heating Applicator for the Simultaneous Radiohyperthermotherapy of Superficial and Shallow-seated Tumors

Abstract

The authors developed and evaluated the performance, using a phantom, of a new capacitive heating applicator designed for the “parallel method” of applying clinical simultaneous radiohyperthermotherapy (SRH) in which electron beam irradiation is provided from above an external capacitive heating applicator for the treatment of superficial and shallow-seated tumors. The trial applicator was made to fulfill the following conditions : (1) use of an electrode plate which does not affect the electron beam depth dose, (2) a uniform tickness to maintain flatness of the electron beam, (3) an attachment site between the electrode and lead wire at the electrode margin to avoid entering the irradiation field, and (4) cooling function to enhance therapeutic gain factor and avoid damage to normal skin tissue. This applicator consisted 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-MeV electron beam and 36 mm with a 15-MeV electron beam, which was comparable to the effect of a conventional irradiation bolus. The temperature distribution produced by the trial applicator was symmetrical on both the right and left from the center of the applicator. The 50% specific absorption rate region was a width of 6.4 cm at a depth of 1 cm from the phantom surface and a width of 2.8 cm at a depth of 3 cm. There have been no previous reports on the development of an external capacitive heating applicator designed for the SRH of superficial and shallow-seated tumors; this is the first report. SRH of these tumors can be performed simply, noninvasively and repeatedly by means of this new applicator.