A DIELECTRIC METHOD FOR MEASURING EARLY AND LATE REACTIONS IN IRRADIATED HUMAN SKIN

Background and purpose: To measure the dielectric constant of irradiat ed human skin in order to test the feasibility of the dielectric measu rements in the quantitation of acute and late radiation reactions. Mat erials and methods: The dielectric constant of irradiated breast skin was measured at an electromagnetic frequency of 300 MHz in 21 patients during postmastectomy radiotherapy. The measurements were performed w ith an open-ended coaxial line reflection method. The irradiation tech nique consisted of an anterior photon field to the lymph nodes and a m atched electron field to the chest wall using conventional fractionati on of five fractions/week to 50 Gy. Fourteen out of the 21 patients we re remeasured 2 years later and the skin was palpated for subcutaneous fibrosis. Results: At 5 weeks the dielectric constant had decreased b y 31 and 39% for the investigated skin sites of the photon and electro n fields, respectively. There was a statistically significant inverse correlation between the mean dielectric constant and the clinical scor e of erythema. An unexpected finding was a decrease of the dielectric constant of the contralateral healthy skin during radiotherapy. Two ye ars later a statistically significant positive correlation was found b etween the dielectric constant at the irradiated skin sites and the cl inical score of subcutaneous fibrosis. Conclusions: Dielectric measure ments non-invasively yield quantitative information concerning radiati on-induced skin reactions. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.