Duncan McCulloch

The effect of low-level 60-Hz electromagnetic fields on human lymphoid cells: II. Sister-chromatid exchanges in peripheral lymphocytes and lymphoblastoid cell lines

Dividing human peripheral lymphocytes from 10 normal adults (5 males and 5 females) as well as lymphoid cell lines from patients with the chromosomal instability syndromes were exposed to low-level 60-Hz sinusoidal electromagnetic fields (EMF). The current density of the electrical field was 30 microA/cm2 while the strength of the magnetic field was either 1 or 2 gauss. The cytological endpoints measured included the frequency of sister-chromatid exchanges per chromosome; the distribution of first-, second-, and third-division cells and chromosome breakage (lymphoblastoid cells only). No statistically significant differences, indicative of EMF effects were observed between the treated and control cells regarding SCE frequency, cell cycle progression or chromosome breakage.

Microwave Heating of Malignant Mouse Tumors and Tissue Equivalent Phantom Systems

Studies were conducted on the free-field heating of mammary tumors on the flank of mice and of tissue equivalent phantoms. A 200 watt, P.M., 2450 MHZ source was marginal in heating 1 cm tumors from room ambient to 38 degrees C. A technique was developed using warm air to raise the thermal baseline of the tumors to body core temperature and microwaves to produce significant hyperthermal levels. This allowed the production tumor temperatures of 45 degrees with greatly reduced microwave power and with significantly more uniform temperatures. However, the non-uniformity in temperature achieved with monodirectional microwave heating is still considered to be excessive: +/- 1 degrees C.

The Effects of Microwaves on Cell Survival at Elevated Temperatures

Since microwaves are used in human cancer therapy, information on specific biological effects of microwaves at elevated temperatures is important. To help supply this information, we exposed mammalian cells (CHO) and bacteria (Serratia marcescens) to hyperthermal temperatures (43, 44, and 45/sup o/C for CHO and 48, 49, and 50/sup o/C for the bacteria) with and without microwave irradiation. Temperature control was maintained by a refrigeration-reheat system and high-velocity water recirculation. The 2450-MHz microwave source was operated in a pulsed mode with power density up to 500 mW/cm/sup 2/. As expected, the survival curve slopes for both cell types increased rapidly with temperature, doubling for each degree Celsius. Microwave irradiation produced no significant change in extrapolation number for either cell type. However, survival curves of CHO cells which received microwaves were steeper by a factor of 1.25 than their sham-irradiated controls. No significant effect on slope was seen with the bacteria. Liquid crystal thermometry revealed a microwave-induced temperature elevation of 0.3/sup o/C in the glass microcapillary exposure tubes. This temperature elevation closely corresponded to the observed difference in survival curve slopes for the CHO cells and suggests a simple thermal origin for that difference.

Techniques for Uniform and Replicable Microwave Hyperthermia of a Model Mouse Carcinoma

Two techniques for localized 2450-MHz hyperthermia of experimental mouse cancers are described. In the far-field approach superficial tumors are encapsulated in 5-cm mold-formed spheres of semi-solid phantom material, then placed in an anechoic chamber on an equipower surface. In the applicator approach, tissues are immersed in a temperature-controlled tissue-equivalent liquid bolus, and are irradiated by time-multiplexed parallel-opposed beams. Both techniques feature microwave bolusing for improved coupling and tumor heating uniformity.

Far-field 2.45 GHz irradiation system for cellular monolayers in vitro

A 2.45-GHz microwave exposure facility was developed for long-term TEM irradiation of cellular monolayers. Culture flasks with cells attached to the inside bottom surface were filled with medium, submerged in a 60 X 60 X 12-cm water bath on the field central axis, and exposed in the far-field 2 m below the ceiling-mounted antenna. A quarter-wave transformer plate increased the power transmitted into the water bath, and treatment temperatures were maintained by closed circulation with an external temperature control reservoir. Power density mapped below the quarter-wave plate indicated uniform TEM fields in the 25 X 25-cm region where flasks were located. With 1 kW of forward power to the antenna, the SAR [W/kg] = 45 exp(-0.607d) where d [cm] is the depth in water at any point within this area.

Acoustical Imaging Techniques Applied to General Transducer Design

The increasing applications of ultrasound in medical diagnosis have been accompanied by corresponding advances in transducer development, as evidenced by the proceedings of this series of symposia. Our research group is investigating ultrasonic bioeffects, an area largely innocent of specialized transducer technology. Some studies employ typical diagnostic ultrasound exposure systems and exposure conditions to simulate clinical insonation in tissue, at the expense of exposure quantification. Other studies are aimed at establishing dose-response relationships and thresholds for ultrasonically-induced effects; in some cases, these experiments are well characterized in terms of exposure conditions, but with few exceptions, the target areas are insonated with very non-uniform beams.

Microwave Heating of Malignant Mouse Tumors Encapsulated in a Dielectric Medium

A new technique for microwave (2450 MHz) heating of C3H mammary tumors is described. 1 cm tumors were encapsulated in 5 cm spheroids of a material dielectrically similar to biological tissues. When similarly heated, encapsulated tumor exhibited far more front-to-back temperature uniformity than unencapsulated tumors. Encapsulation also improved coupling of microwave heating fields. Tissue-simulating spheres were microwave-heated to the same temperatures in an anechoic range. Central temperature distributions were similar to those in the encapsulated tumors and agreed with theoretical predictions.