A theoretical comparison of energy sources - microwave, ultrasound and laser - for interstitial thermal therapy

A number of heating sources are available for minimally invasive thermal th erapy of tumours. The purpose of this work was to compare, theoretically, t he heating characteristics of interstitial microwave, laser and ultrasound sources in three tissue sites: breast, brain and liver. Using a numerical m ethod, the heating patterns, temperature profiles and expected volumes of t hermal damage were calculated during standard treatment times with the cond ition that tissue temperatures were not permitted to rise above 100 degrees C (to ensure tissue vaporization did not occur). Ideal spherical and cylin drical applicators (200 mu m and 800 mu m radii respectively) were modelled for each energy source to demonstrate the relative importance of geometry and energy attenuation in determining heating and thermal damage profiles. The theoretical model included the effects of the collapse of perfusion due to heating. Heating patterns were less dependent on the energy source when small spherical applicators were modelled than for larger cylindrical appl icators due to the very rapid geometrical decrease in energy with distance for the spherical applicators. For larger cylindrical applicators, the ener gy source was of greater importance. In this case, the energy source with t he lowest attenuation coefficient was predicted to produce the largest volu me of thermally coagulated tissue, in each tissue site.