SIMULATION OF BIDIRECTIONAL ULTRASOUND HYPERTHERMIA TREATMENTS OF NECK TUMORS

The temperature distributions produced in neck tumours by using either a single, scanned transducer (a unidirectional scan) or two separate transducers whose axis are perpendicular (a bidirectional scan) were s imulated. The three-dimensional neck model included separate anatomica l regions for the normal neck muscle tissue, the tumour, the spinal co lumn and the trachea (no large blood vessels). The effets of variation s in the transducer frequency and f number, the tumour size and locati on, and the normal and tumour blood perfusion rates were studies. The best simulated temperature distributions were produced by bidirectiona lly scanned, 2 MHz, f number 2.0 ultrasound transducers whose powers w ere modulated as a function of position. The simulated temperature dis tributions from such modulated bidirectional scans were significantly better than those of both unidirectional and unmodulated bidirectional scans. The 1-MHz transducers generally produced hot spots at the tiss ue-spine and/or tissue-trachea interface. The 3-MHz transducers elimin ated those deep hot spots but created other hot spots close to the ski n surface, and did not adequately heat the deeper regions of the tumou r. These results from the simplified computer simulations may be used to guide the construction of improved ultrasound hyperthermia systems for the treatment of neck tumours.