Characteristics of acoustic wave propagation in dermis for the diagnosis of the superficial tissue damage in radiation therapy

Measurement of tissue radiation damage quantitatively in radiation therapy is very important to optimize the therapeutic treatment. Ionized radiation induces homogenization of the extracellular matrix which is synthesized by fibroblast and the randomization of the orientation of the collagen fibers in dermis. If the dermis is exposed by ionized radiation, a thermal acoustic shear wave which propagates in dermis becomes harmonic wave; Otherwise, an inharmonic wave is expected because of inhomogeneous and the anisotropic properties of dermis. A polarized optical heterodyne interferometer was setup in order to measure the transverse displacement of the shear wave in order to analyze the propagation mode of the shear wave in dermis. The detection sensitivity of the displacement was 1 nm and the dynamic range was 300 nm in this arrangement. The lowest dose that can be detected by the exposure of 4 MeV radiation on porcine dermis was 1 cGy.