A REFLECTED-SCANNED ULTRASOUND SYSTEM FOR EXTERNAL SIMULTANEOUS THERMORADIOTHERAPY

The simultaneous delivery of hyperthermia and ionizing radiation has t he potential to improve clinical outcome. To this purpose, a scanning ultrasound reflector-linear array system (SURLAS) with the ability bot h to conform power to superficial volumes and to operate concomitantly with medical linear accelerators is currently under development. In t his purpose-specific design, the ultrasound waves generated by a linea r array are directed toward a scanning reflector which in turn deflect s the waves toward the target. In previous experiments, the technical feasibility of this design was demonstrated. Here, we are concerned wi th the minimization of a key design parameter, namely, the array eleme nt size, in order to minimize the amount of attenuating/scattering wat er-equivalent medium that a photon or a electron beam passes through b efore entering the target. First, the SURLAS design is described. Seco nd, an acoustic model to compute power deposition patterns is presente d. This model is coupled to a bioheat transfer model for computation o f temperature fields. Third, an analysis is performed to determine the minimum array element size for three target categories. Finally, acou stic fields and temperature distributions induced by the SURLAS for th e three target categories are presented. The analysis and simulations show that the SURLAS has the potential to induce uniform temperature d istributions in large superficial volumes with small enough elements t o allow simultaneous delivery with electron beam therapy.