Accurate quantification and delivery of thermal dose to cells in culture

Abstract

HIFU treatments involve raising the temperature of target tissue above 60°C in short (~2 s) bursts. At higher temperatures, shorter times are required to induce a given deleterious effect: the Sapareto-Dewey thermal dose equation is often used to relate the time to produce a biological effect at one temperature to the time to produce equivalent effects at another. A heating chamber was developed to deliver controlled thermal doses to cells in culture under continual observation by differential interference contrast microscopy. The system comprised of a cell culture well and cover slip coated with a transparent electrode inserted into a microscope stage with electrical contacts. Thermal doses were delivered by applying programmed current-time profiles and using a PID controller to rapidly raise and maintain the temperature of the chamber above 37°C while monitoring with fine wire thermocouples. Initially, HeLa cells in monolayer culture were imaged before, during, and after heating. Visible changes in cell shape and adhesion began shortly after raising the temperature by 8°C and progressed during a heating period of 20 min, continuing for more than 12 h after the cells were returned to 37 °C. No such changes were observed in control cells. Results will be presented exploring the validity of the S-D relationship for shorter, higher temperature exposures.