ANIMAL STUDIES WITH A DEVICE FOR FOCUSED DEEP HEATING

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A new hybrid radiofrequency applicator consisting of inductive, capacitive, and grounded elements whose phase and/or spatial orientation are variable has previously been shown to be capable of precisely focused heating at depths of 10cm or more in phantom models of homogeneous dielectric. This device will be utilized to study the practicality and/or the safety of precisely focused deep heating in minipig carcasses complex phantoms and living anesthetized minipigs. Focal heating will be attempted in anatomic sites in the abdomen, pelvis, thorax, and CNS selected because of current difficulties in applying hyperthermia in tumors in these locations. Initially, power deposition patterns in minipig carcasses and complex phantoms of minipig carcasses at thermal equilibrium will be monitored using invasive non-field perturbing probes during heating. Subsequently, two dimensional heating patterns at the surface and in various planes through transected phantoms will be determined using thermally sensitive liquid crystal paper and/or a thermographic camera. Data on sites of maximum power deposition in phantoms will be used to determine optimum placement for invasive temperature monitoring probes during RF heating in living anesthetized animals. Heating patterns and rates of heating in animal phantoms and living anesthetized animals will be correlated with applicator configuration, tuning, spatial orientation of the sample, and incident and reflected power. The safety of using the device in living animals will be determined by careful monitoring of vital signs during RF application and short term observation of animals for surface or deep electrical burns outside the desired treatment area. If the above tasks are successfully accomplished, in years 2-4 the safety of heating specific sites in predetermined patterns to predetermined temperatures will be studied by observation of animals over 1 month and by serial laboratory tests, x-rays, and pathologic studies specific for each anatomic site heated. If these results are satisfactory an attempt will be made to gain experience in treatment of deep seated spontaneously arising tumors in domestic animals which are not considered candidates for conventional therapies. The long term goals of this project are to further develop devices and methodologies capable of applying deep precisely focused hyperthermia alone and in combination with radiotherapy and regional chemotherapy to tumors within the abdomen, thorax, pelvis, and central nervous system. At present, no totally satisfactory systems for precisely focused deep hyperthermia are available.