Calculating the response of isotropic light dosimetry probes as a function of the tissue refractive index.

The response of an isotropic light dosimetry probe as function of the tissue refractive index (n) has been calculated using diffusion theory. The response has also been measured in a collimated light beam with the probe in air, water (n = 1.33), ethylene glycol (n = 1.43), and glycerin (n =1.46). For a 3.2-mm diam probe with little light absorption, the theoretical result depends only on n and differs from the experimental data by not more than 6%. For a 0.8-mm diam probe with some light absorption, excellent agreement between theory and experiment is obtained by adjusting the absorption and the reduced scattering coefficients of the probe material.