Brain hyperthermia: I. Interstitial microwave antenna array techniques--the Dartmouth experience

Microwave antennas of various designs were inserted into arrays of nylon catheters implanted in brain tumors with the goal of raising temperatures throughout the target volume to 43.0 degrees C.

All antennas were flexible, and included dipole, choke dipole, modified dipole, and helical designs driven at 915 or 2450 MHz. Antennas were tested in brain-equivalent phantom in arrays. Phase shifting and phase rotation techniques were incorporated into the treatment system to steer power in the tumor, assisted by a treatment planning computer that predicted power deposition patterns and temperature distributions. Choke antennas were designed and tested to reduce a dependence of the central power location on depth of insertion into tissue. Temperature data analysis used only central and orthogonal axes mapping data measured at 2.0 mm intervals.

A total of 23 patients were treated, using from one to six microwave antennas. Minimum tumor temperatures, averaged over the 60 min treatment, ranged from 37.2-44.3 degrees C (mean 40.0 degrees C) and maximum average tumor temperatures ranged from 46.5-60.1 degrees C (mean 49.1 degrees C). The percentage of all measured temperatures reaching therapeutic levels (> or = 43.0 degrees C) was 70.9. T90, the temperature at which 90% of all measured temperatures equaled or exceeded, was 40.8 degrees C, and T50 was 44.2 degrees C.

Patient data analysis showed that the array of four dipole antennas spaced 2.0 cm apart were capable of heating a volume of 5.9 cm (along the central array axis) x 2.8 cm x 2.8 cm.