Purpose: An early indicator of radiation induced skin reactions would be a valuable tool for mitigating skin toxicity in radiation therapy patients. Based on previous mouse studies, a tomographic reconstruction of skin effusivity using a flash pulsed thermal imaging system could be used as an early detection system, but translation of the technique to human subjects requires additional development.
Methods: Due to the finite speed of heat propagation, one can calculate the thermal properties of materials at depth based on the decay of surface temperature after impulse heating. A pulsed thermal imaging system has been employed using two flash lamps and an infrared camera. Vinyl tape with measured thermal properties was used as a fiducial and effusivity values of the skin beneath the tape were calculated to a depth of 0.5 mm. Effusivity measurements of known materials were performed to evaluate the accuracy of the system as well as several skin measurements to determine precision.
Results: The thermal effusivity of vinyl tape was first calibrated using the known value of water (1588 W âˆšs/(mÂ² Â°K)). Calculated values of tape effusivity were found to be 590Â±7.5 W âˆšs/(mÂ² Â°K). The effusivity of other materials underlying the vinyl tape were measured as a function of depth by normalizing to the effusivity of the tape. Using this tape calibration value, the effusivity of borosilicate glass was found to be 1370 W âˆšs/(mÂ² Â°K), which differs <2% from published values. Nine separate measurements of untreated skin of the forearm were made over the course of a week and found to be 1406 W âˆšs/(m2 Â°K) to a precision of Ïƒ=20 W âˆšs/(mÂ² Â°K).
Conclusion: We have validated the precision and repeatability of the measurement apparatus, allowing detection of effusivity changes which may manifest as a precursor to skin toxicities grade 2 or higher.