Computational study of necrotic areas in rat liver tissue treated with photodynamic therapy.

BACKGROUND: Photodynamic therapy (PDT) is an alternative treatment method for liver metastatic cancer worth exploring.

METHODS: This study implements a computational model of metastatic rat liver tissue subjected to superficial irradiation, after administration of 5,10,15,20-Tetrakis(3-hydroxyphenyl)chlorine (mTHPC). Spatial and temporal distributions of fundamental PDT dosimetric parameters are presented, along with calculation of necrotic distance and necrotic area percentage. Moreover, an algorithm able to calculate the minimum irradiation time needed in order to achieve various values of necrotic depth is coded.

RESULTS: The intratissue distributions show that light penetration depth is approximately 1.5 mm for all fluence rate (φ) values in direction of z axis. Moreover, necrosis at r axis (horizontal axis) extends outside beam's geometrical edges at distance equal up to 55.3% of its radius. It is also noticed that both φ and concentration of ground-state photosensitizer ([S0 ]) can increase the necrotic distance, in a steeper manner at lower [S0 ] values. The irradiation time needed in order to achieve various values of necrotic depth is independent of φ for the upper tumor layers but is greater in orders of magnitude for deeper lying layers and low φ values.

CONCLUSIONS: Increasing light fluence rate appears to be a more productive method than increasing photosensitizer concentration for inducing necrosis, especially in larger tumors. Finally, our results show that high φ values are necessary in order to maintain clinically applicable irradiation times.