Optical characteristics of human lung cancer for photodynamic therapy with measured absorption and reduced scattering coefficients.

Significance: The optical characteristics of a human lung, such as the light distribution in the tissue, are crucial for evaluating the light delivery of photodynamic therapy (PDT) for peripheral lung cancer.

Aim: The light distribution in the human lung is analyzed with absorption ( ${\mu }_a$ ) and reduced scattering ( ${\mu }_s^{\text{'}}$ ) coefficients measured ex vivo for normal, carbon-deposited, and tumor tissues.

Approach: The ${\mu }_a$ and ${\mu }_s^{\text{'}}$ spectra were measured using a double-integrating-sphere optical system and inverse Monte Carlo technique. The measured values were used to perform a light distribution analysis using a Monte Carlo light transport simulation.

Results: The ${\mu }_a$ values varied between tissue types owing to the influence of carbon deposition, blood volume fraction, and oxygen saturation, whereas the ${\mu }_s^{\text{'}}$ values showed almost no differences between tissue types. The simulation results showed that carbon deposition in the surrounding tissue and oxygen saturation variability had almost no effect on PDT light delivery to a tumor with a 10-mm-diameter sphere.

Conclusions: Our analysis revealed the influence of the optical characteristics of the lung tissue on PDT light delivery. Integration of these results with the photosensitizer dose and the degree of necrosis changes will allow us to provide more clinically relevant insight in determining PDT dosimetry.