The clinical outcome of photodynamic therapy (PDT) may be improved by the accurate knowledge about the light
distribution within the tissue. Optical properties [absorption coefficient (μa), scattering coefficient (μs), anisotropy factor
(g), refractive index, etc.] of tissues help us realizing a light propagation through the tissue. The aim of this study is
acquisition of the knowledge of light propagation within tissue with the optical property of mouse tumor tissue
performed PDT. We evaluated the optical property of mouse tumor tissue before and after PDT using the double
integrating sphere setup and algorithms based on the inverse Monte Carlo method in the wavelength range from 350 to
1000 nm. During PDT, the reduced scattering coefficient spectra were decreased entirely after 5 and 10 min irradiation.
1, 2, 7 days after PDT, the absorption coefficient was increased in the wavelength range from 400 to 660 nm. And, the
reduced scattering coefficient at the wavelength of 664 nm was increased with the passage of time. These results are used
for medical diagnostic applications for the quantitative assessment of the PDT effect. 7 days after PDT, the reduced
scattering coefficient at the wavelength of 664 nm was increased significantly from 0.64 mm-1 to 1.24 mm-1, which
results in the optical penetration depth decreased from 1.49 mm to 0.84 mm, respectively. To ensure the effective
procedure, an adjustment of the laser parameter for the decreasing penetration depth is recommended for a second PDT.