A reflected-scanned ultrasound system for external simultaneous thermoradiotherapy

The simultaneous delivery of hyperthermia and ionizing radiation has the potential to improve clinical outcome. To this purpose, a scanning ultrasound reflector-linear array system (SURLAS) with the ability both to conform power to superficial volumes and to operate concomitantly with medical linear accelerators is currently under development. In this purpose-specific design, the ultrasound waves generated by a linear array are directed toward a scanning reflector which in turn deflects the waves toward the target. In previous experiments, the technical feasibility of this design was demonstrated. Here, the authors are concerned with the minimization of a key design parameter, namely, the array element size, in order to minimize the amount of attenuating/scattering water-equivalent medium that a photon or a electron beam passes through before entering the target. First, the SURLAS design is described. Second, an acoustic model to compute power deposition patterns is presented. This model is coupled to a bioheat transfer model for computation of temperature fields. Third, an analysis is performed to determine the minimum array element size for three target categories. Finally, acoustic fields and temperature distributions induced by the SURLAS for the three target categories are presented. The analysis and simulations show that the SURLAS has the potential to induce uniform temperature distributions in large superficial volumes with small enough elements to allow simultaneous delivery with electron beam therapy.