Rapid heating: critical theoretical assessment of thermal gradients found in hyperthermia treatments.

There is increasing evidence that many hyperthermia failures are closely related to the large variability of temperatures found in the treatment field. These are linked to thermal gradients near the treatment boundary, vascular perfusion differences, localized cooling, and poor distribution of energy deposition in the tissues. One way of reducing the temperature gradients is to replace traditional heating treatments of 30-60 min by a rapid heating technique, in which the treatment time is a few seconds combined with higher treatment temperatures. The purpose of this paper is to model potential advantages of using various rapid heating protocols, and to compare them with traditional treatments. Theoretical models (in agreement with clinical treatments) suggest that traditional hyperthermia treatments often do not produce the necessary temperature homogeneity needed to kill the last malignant cells in the tumour due to cooler regions in the field. The simulations presented in this paper suggest that much shorter treatment times (1-10 s) should give significant improvements in the treatment field for both the temperature homogeneity and equivalent thermal doses.