A well-known disadvantage of a radiofrequency-capacitive device for deep-seated tumours is preferential heating of the subcutaneous fat tissue. The authors previously developed the hyperthermia with their own external cooling unit and achieved strong superficial cooling, and reported its usefulness for the reduction of the preferential heating. The purpose of the present study was to evaluate the effect of hyperthermia with strong superficial cooling on the treatment results for unresectable or recurrent colorectal cancers. From 1986 to 2002, 44 patients with primary unresectable or locally recurrent colorectal cancer treated with thermoradiotherapy were analysed retrospectively. The patients with obesity as a subcutaneous fat thickness more than 3 cm, a high age or other serious complications did not undergo therapy. The results were compared between 17 cases with strong superficial cooling treated after 1997 (Group A) and 27 cases without strong superficial cooling treated before 1996 (Group B). Significant differences in thermometry data of Tmax, Tave and Tmin were noted between Groups A (45.3, 44.4 and 43.6°C, respectively) and B (42.9, 42.0 and 41.1°C, respectively) (p < 0.01). Complete response plus partial response rates were better for Group A than for Group B (59 versus 26%, p = 0.05). Multivariate analysis by logistic regression to evaluate the effects of certain factors on complete response plus partial response was strongly correlated with strong superficial cooling (p < 0.05). The median survival times for overall survival were 24.3 months for Group A and 17.1 months for Group B (p < 0.05). Eight-megahertz radiofrequency-capacitive regional hyperthermia with strong superficial cooling is potentially useful for improving treatment results in unresectable or recurrent colorectal cancers.
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