Combining target coverage and hot-spot suppression into one cost function: the hot-to-cold spot quotient

Microwave hyperthermia treatment planning (HTP) is a multi-objective task for which several cost functions have been suggested over the years. The power distribution inside the patient, achieved by amplitude and phase steering of the applicator array, must fulfill diverse requirements. On the one hand, high and homogeneous target power deposition is required for temperature elevation. On the other, healthy tissues should not be subjected to excessive heating and hot-spots outside the target should be suppressed. To these ends, two major SAR- based indicators are currently used as cost functions in clinical HTP, albeit with slightly different meanings: the HTQ and the TC. We propose a novel cost function, termed the hot-to-cold spot quotient (HCQ), aiming at simultaneous target coverage and hot-spot suppression. We show that the HCQ yields HTP solutions that represent a good compromise between the HTQ- and TC-optimal ones for two realistic cases in both single- and multi-frequency settings.