Control of heating pattern from interstitial instrumentation [thermal patient therapy]

Interstitial instrumentation (ultrasound, radiofrequency, microwave) is used in clinics for thermal therapy of many maladies (cancer, thrombosis, hemorrhage, etc.). This presentation focuses on the usefulness of the interstitial instrumentation in thermal therapy of brain cancers. We show that appropriate placement of the applicators in the array can produce an irregular heating pattern. Using the example of a waveguide ultrasonic applicator array, we consider array geometry of vertical applicators and applicators at 20° to the horizontal. Acoustic scans for the two systems make evident that evaluation of the heating pattern from measurement of the instrumentation power deposition is reliable only for the case of simple array geometry. We demonstrate that an FEA approach, however, enables prediction of the heating patterns for any array geometry. Our FAE computations for the case of complicated array geometry gave intricate heating patterns that are impossible to predict from measurement of the instrumentation power deposition. Also, the FEA approach illustrates that the heating with more complex array reduces incidental heating, an undesired effect. We demonstrate that power measurements and FEA computations have to be integral steps in evaluation of an instrumentation efficacy for heating.