Limits on focused ultrasound for deep hyperthermia

It becomes increasingly difficult for ultrasound to noninvasively heat larger tumor volumes at depth without overheating intervening normal tissues. For a given acoustic window, there exists a maximum tumor volume at a given depth which can be treated effectively without causing “hot spots” in the normal tissues, even if “ideal” applicators and power deposition techniques are applied. In this paper, the upper bound on the radii of treatable spherical volumes under given physical, anatomic, and physiological constraints is determined. Parametric studies are performed to determine relationships between the upper bound radius and constraints such as acoustic window size, tumor depth, attenuation rate, the tolerable temperature in normal tissues, and blood perfusion rate