Anatomy-resolved digital twin framework for personalized light dosimetry in lung therapies

Light therapies, such as photobiomodulation and photodynamic therapy, have demonstrated effective therapeutical response. However, external irradiation and targeting internal organs is challenging due to high light attenuation and the interindividual anatomical variability, strongly affecting light dosimetry. When considering lung diseases, such as pneumonia and inflammatory conditions, light dosimetry using transcutaneous delivery must consider the total light path from skin coupling through thoracic tissues to the fluence rate reaching the lungs. We here present a computational model based on Monte Carlo simulation developed in house to determine the light dosimetry in the lungs for different wavelengths in normal and diseased lungs. The simulation uses the actual anatomical models derived from human CT scans to generate 3D representations of the thoracic cavity, including 12 distinct tissue types. The lungs were segmented into normal, collapsed regions, infiltrate, and blood vessels. Wavelength-dependent absorption and scattering coefficients for each tissue type were estimated by the reported data in the literature. Our analysis focused on normalized energy deposition profiles defined as µ_a*fluence rate and fluence rate distributions within each lobe from normal, focal, and diffuse pneumonia, and COVID-19 conditions, under different irradiation positions. The results reveal significant variations in energy deposition and fluence rate distribution across different lung conditions and irradiation parameters, highlighting the need for individualized light dosimetry planning.