Development of a guideline for the water bolus temperature in superficial hyperthermia.

PURPOSE: The research presented in this work investigates the influence of the water bolus temperature on temperature distributions in tissue during superficial hyperthermia treatments using Lucite cone applicators. The goal of the research was to develop a guideline for the selection of the water bolus temperature based on 3-D electromagnetic and thermal modelling.
METHODS: A 3-D model was set up to simulate an abstraction of the treatment. In the model a convection coefficient for the water bolus to skin surface was employed. In order to simulate the heat balance as realistically as possible, convection coefficients were measured for different water boluses and ranged from 70-152W (m(2) K)(-1). The model was evaluated by simulating three clinical treatments and comparing the outcome of the model to the clinical measurements.
RESULTS: The model was found to predict the temperature distribution well on a global view; root mean square errors between 0.66-1.5 degrees C were found for the three treatments. For some temperature probes a deviation of 1.5-2.0 degrees C between measured and predicted temperature was found. These large deviations can be explained by local variations in cooling by blood vessels, tissue inhomogeneity, a varying convection coefficient of the water bolus and of course the complexity of the anatomy.
CONCLUSIONS: The model was used to set up guidelines for the water bolus temperature selection in clinical practice for the target depths and applicator arrays used in the Rotterdam Erasmus Medical Center.