Techniques for intraoperative hyperthermia with ultrasound: the Dartmouth experience with 19 patients

Over the course of 3 years, tumours of 19 patients were heated with ultrasound in the operating room during surgical resection. Immediately following intraoperative radiation therapy, thermocouples were inserted into tumour and adjacent normal structures. Patients were then given a 60-min heat treatment with ultrasound after a 10-15-min heatup period. Temperatures were measured at a total of 133 fixed locations for the 19 patient series. Temperature mapping was done in the tumour volume when logistically feasible. Treatment sites included colorectal (n = 3), portahepatus (n = 1), pancreas (n = 7), liver (n = 1), pelvis (n = 3), sacrum (n = 2), and abdomen (n = 2). A sterile, constant-volume water circulating system was utilized to control surface temperatures. Three generations of completely immersible transducers were designed over the course of this study with a 4-cm height specification. Since the ultrasound transducer was assembled on the sterile field during surgery, a 1, 2 or 3 MHz ceramic element was placed in either a 6, 8 or 10 cm diameter aluminium housing to conform the acoustic field to the tumour size. Average of the maximum temperatures attained was 46.6 degrees C. Temperature with which 90% of all measured points equalled or exceeded (T90) was 39.2 degrees C. The T50 was 42.9 degrees C. This compared favourably with T90 and T50 of 38.8 and 41.9 degrees C, respectively, in our outpatient clinic series, in which superficial tumours were treated with a similar external applicator, and patient tolerance was often a treatment limitation.