P2G-4 Optimization of the ´En Face´ Ultrasound Component in Hybrid RF/US Applicators Designed for Hyperthermia and Heat-Modulated Drug Delivery in Treatments of Locally Advanced Breast Cancer

Simulations of thermal therapy show that ultrasound (US) phased arrays noninvasively heat small regions to relatively high temperatures and that radio-frequency (RF) electromagnetic phased arrays noninvasively deliver relatively mild temperatures to larger volumes. Individually, neither modality can achieve therapeutic temperatures continuously throughout a large breast tumor without severely overheating normal tissue. However, preliminary simulations indicate that US combined with RF attains higher, more uniform temperatures than either modality alone. This result motivates the design of optimal hybrid RF/US phased arrays for hyperthermia and for thermal targeting of drug delivery in treatments of locally advanced breast cancer. In one such hybrid array structure, the ´en face´ ultrasound component is varied from 1MHz to 3 MHz. Both intervening tissue heating and bone heating beyond the tumor target are evaluated in this model, which shows that the optimal ultrasound frequency for this configuration is 1.9MHz for an ultrasound attenuation of 0.5dB/MHz/cm and 1MHz for an ultrasound attenuation of 1dB/MHz/cm. For both attenuation values, ultrasound is primarily focused in the core of the tumor and the portion of the tumor that is located closest to the ultrasound phased array, whereas the RF component delivers therapeutic heat to specific portions of the tumor periphery. This hybrid therapy approach, which fractionates heat delivered to the tumor volume with RF and US heating contributions, is expected to improve hyperthermia temperature distributions and enhance thermally-modulated drug delivery for treatments of locally advanced breast cancer