Introduction

Cancer is a disease that has afflicted over 13 million Americans since 1990. 41% of the people diagnosed with cancer will die from the disease within five years. If treated properly, many patients may have life extended 5,10 years or more and, in many cases are cured. Chestwall recurrence of breast carcinoma is a particularly virulent type of cancer that if left untreated can quickly metastasize to vital organs and cause death. Chestwall recurrence, in its early stages often has the form of hard plaque-like disease on the surface of the skin, spreading rapidly to cover large amounts of the patient's torso. Hyperthermia treatment for chestwall recurrence is an adjuvant therapy used most often with chemo or radio-therapy. Successful hyperthermic treatment for chestwall recurrence requires that the cancer be treated in its entirety. Current heating techniques can not successfully heat areas larger than 13cm by 13cm and can not cover highly contoured regions such as the human torso i.e. around the rib cage. The applicator design optimized in this effort is highly flexible and light in weight and has the potential to treat much larger areas over contoured anatomy. The hyperthermia applicator design investigated in this work is shown in figures 9 and 10. The applicator consists of an array of microstrip patch antennas printed on an extremely thin and flexible printed circuit board material.

Previous generations of these CMA hyperthermia applicators have

already proven that they can produce adequate heating. Early prototypes lacked optimization of certain microwave engineering considerations however. It was felt that if microwave transmission line matching techniques were applied to the microstrip feedline network that a large gain in efficiency could be realized. Four microwave-matching techniques were applied to the original CMA applicator design:

  1. quarter wave transformers
  2. meander lines
  3. variations in microstrip width
  4. the loss-less 3dB T-junction power divider

The microwave transmission line network parameters such as, return loss, input impedance and standing wave ratio were determined with a vector network analyzer. The electric field pattern of the antenna array was characterized by mapping the field with a miniature electric field probe in a tank of liquid muscle-tissue equivalent phantom.

It was found that the microwave network parameters for the optimized antenna array were all much improved. The average return loss was essentially doubled. An important result found was that the variance in the measured parameters was dramatically less for the optimized board. The electric field patterns for the non-optimized and optimized arrays were not quantitatively different. While the radiated electric field distributions were not different, the input power required to produce them was. The optimized array required almost half as much power to produce the same output as the non-optimized array.

It has been shown that the flexible printed circuit board DCC hyperthermia applicator can heat a large area of superficial tissue. Early prototypes of this type of applicator worked but were inefficient. The newest optimized antenna array has dropped the power required down to almost half of the previous levels while reducing the variance in power required to each antenna in the array to a fraction of the non-optimized levels.

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