Evaluation of captive bolus applicators.

Three square (L, M, MS) and one rectangular (HN) applicators with captive boluses were provided by the Clini-Therm Corporation for evaluation. Surface cooling is achieved by attaching a mineral oil captive bolus to the built in water-circulating tubes at the aperture of the applicators. These applicators were tested on a phantom with a 2-cm fat slab over 10-cm-thick muscle. Surface and sagittal heating patterns were obtained using a thermograph. All captive-bolus applicators have heating patterns similar to that of the regular Clini-Therm applicators. Due to hot spots at the edges of the applicators where the E fields terminate, these modified applicators should not be placed in direct contact with patients when boluses are not used. Tests with Clini-Therm regular water bolus instead of the captive oil bolus indicated that the orientation of water flow should be parallel to the E field to minimize perturbation of the heating patterns. Thermal conduction studies showed that the captive bolus reacts too slowly for skin temperature control. The modified captive bolus applicators did not improve the performance of the system.