# Modeling of Singlet Oxygen Generation and Thermal Effects During Laser–Tissue Interaction

## TL;DR

This paper models how laser therapy affects tissues by simulating energy deposition, heat transfer, and chemical reactions during photodynamic therapy.

## Contribution

A novel modeling approach integrating laser energy, bioheat transfer, and PDT reactions with thermal-dependent parameters.

## Key findings

- Laser energy distribution was modeled using the optical diffusion equation.
- Triplet and singlet oxygen concentrations were simulated with PDT reaction equations.
- Abnormal tumor vasculature was modeled using the Krogh cylinder approach.

## Abstract

This paper presents an analysis of the phenomena that occur during photodynamic therapy (PDT). For this purpose, models of laser energy deposition, bioheat transfer, and reactions occurring during the PDT process were used. Light distribution was estimated on the base of optical diffusion equation, while for the bioheat analysis the Pennes formula has been used. The PDT reaction model includes equations related to the concentration of triplet oxygen, photosensitizer, and singlet oxygen. The tissue perfusion coefficient and the effective scattering coefficient have been assumed to be thermally damage dependent. Changes in blood velocity in capillary, which affects maximum oxygen supply in PDT model, were also considered. A way of modeling the abnormal vascular pattern in the tumor area was also proposed, and the initial distribution of triplet oxygen in the tumor region was determined on the Krogh cylinder model. At the stage of numerical calculation, the boundary element method, the finite difference method, and the shooting method were used.