Treatment planning for hyperthermia with ultrasound phased arrays.

摘要

Hyperthermia cancer therapy applies the cytotoxic effects of heat to tumor cells. All cancer modalities attempt to eliminate malignant cells and minimize normal tissue damage, and for hyperthermia, this involves maximizing therapeutic efficacy and avoiding patient pain. To achieve these goals, a hyperthermia applicator must adapt to individual patients and specific sites, which suggests the application of multiple element arrays. Array systems focus energy within a specified target volume, and, in particular, ultrasound phased arrays allow flexible and precise control of the power deposition. Ultrasound phased arrays provide reasonable values of penetration depth and spot size, crucial parameters for localized hyperthermia in deep tumors.; Flexible systems such as ultrasound phased arrays require an optimization procedure prior to each patient treatment. This process, patient treatment planning, consists of thermal, acoustic, and geometric optimization procedures, computations which determine the individual array element amplitudes and phases and which orient the array system relative to the patient. These three routines utilize bioheat transfer, multiple focus synthesis, and ray tracing concepts, respectively. For ultrasound phased arrays, thermal procedures specify an acceptable temperature range both internal and external to the tumor, computing the location and intensity of the necessary focal points, and acoustic methods calculate the element phases and amplitudes corresponding to the requirements of the focal point distribution. In addition, geometric treatment planning maximizes the active aperture and deactivates array elements that irradiate air or bone obstructions.; These three steps constitute a framework for hyperthermia treatment planning, where ultrasound phased arrays conform to acoustic windows and deliver preferential heating to a tumor volume. Patient image data for cancer of the prostate, a difficult target situated in the midst of multiple pelvic bone obstructions, illustrates the geometric treatment planning algorithm and other tools for treatment analysis. In addition, the two other procedures demonstrate how ultrasound phased arrays generate acoustic fields which deliver energy to the tumor and distribute power over a wide surface area, reducing undesirable 'hot spots' and surface heating.