BRAIN HYPERTHERMIA .1. INTERSTITIAL MICROWAVE ANTENNA-ARRAY TECHNIQUES - THE DARTMOUTH EXPERIENCE

Purpose: Microwave antennas of various designs were inserted into arra ys of nylon catheters implanted in brain tumors with the goal of raisi ng temperatures throughout the target volume to 43.0 degrees C. Method s and Materials: All antennas were flexible, and included dipole, chok e dipole, modified dipole, and helical designs driven at 915 or 2450 M Hz. Antennas were tested in brain-equivalent phantom in arrays. Phase shifting and phase rotation techniques were incorporated into the trea tment system to steer power in the tumor, assisted by a treatment plan ning computer that predicted power deposition patterns and temperature distributions. Choke antennas were designed and tested to reduce a de pendence of the central power location on depth of insertion into tiss ue. Temperature data analysis used only central and orthogonal axes ma pping data measured at 2.0 mm intervals. Results: A total of 23 patien ts were treated, using from one to six microwave antennas. Minimum tum or temperatures, averaged over the 60 min treatment, ranged from 37.2- 44.3 degrees C (mean 40.0 degrees C) and maximum average tumor tempera tures ranged from 46.5-60.1 degrees C (mean 49.1 degrees C). The perce ntage of all measured temperatures reaching therapeutic levels (greate r than or equal to 43.0 degrees C) was 70.9. T-90, the temperature at which 90% of all measured temperatures equaled or exceeded, was 40.8 d egrees C, and T-50 was 44.2 degrees C. Conclusion: Patient data analys is showed that the array of four dipole antennas spaced 2.0 cm apart w ere capable of heating a volume of 5.9 cm (along the central array axi s) X 2.8 cm X 2.8 cm.