Numerical light dosimetry in murine tissue: analysis of tumor curvature and angle of incidence effects upon fluence in the tissue

Abstract

In order to better understand light dosimetry issues for photodynamic therapy (PDT), we have used various tumor and normal tissue geometries to develop a diffusion model of light transport in tissues. We hypothesize that tumor tissues with curved surfaces will have significantly different internal fluence distributions, as compared to tissues with flat surfaces. Using a mouse subcutaneous tumor and rear limb muscle model we compared the internal fluence values within the tissue. In addition, numerical simulations for these corresponding tissue geometries and laser light incidence angles were made. Assuming that the relative photon fluence in the tissue can be accurately modeled by the diffusion equation, we used a finite element approach to approximate the distribution inside the tissue. Meshes with different geometries (flat and curved with different curvatures) were used in this study to mimic the tumor and leg geometries of the murine tumors treated in the lab. Results suggest that tissues surface geometries and incidence angle of light can significantly alter the photon fluence inside the tissue. The photon fluence difference for an 8 mm diameter, curved surface mouse tumor vs. flat muscle tissue can be as high as 20%. In general, the greater the tissues curvature, the greater the potential loss in light fluence is. In summary, our data demonstrates the importance of tissue surface geometry and the incidence angle of light in determining optimal PDT light dosimetry, and indicates that comparisons between tissue geometries must be carried out with attention to differences in the internal optical distribution.

Performance evaluation of cylindrical fiber optic light diffusers for biomedical applications

“…Mechanical stress due to repeat use may result in exaggerated forward scattering thus the emission characteristics of cylindrical diffusers have to be validated prior to repeat use. Treatment planning programs, currently under development by various groups [15][16][17] should consider anisotropic emission by cylindrical diffusers in tissues with low albedo or in hollow organs. We propose that manufacturers of cylindrical light diffusing devices provide longitudinal, polar, and azimuth emission data for each product with the longitudinal emission being sampled at least at half the mean free path given by m eff of the tissue at the intended treatment wavelength, or equal to 1.2 mm for human prostate at 633nm [18] and 0.21 mm for adult human white matter [19] as two examples.…”

Estrategias aplicativas de la terapia fotodinámica del cáncer empleando LEDs en lugar de láseres basadas en estudios sobre cultivos de células tumorales, modelos animales y rutas de traslación a pacientes

“…Hay una creciente evidencia que muestra que la hipoxia (y la posterior reoxigenación) puede tener un profundo impacto en la progresión maligna y en la recuperación del tejido luego de aplicada la terapia [249] [250]. Cualquiera que sea el caso, queda en evidencia la importancia de la geometría del tejido y el ángulo de incidencia de la luz para determinar la dosimetría óptima para una TFD efectiva, en consonancia con lo indicado en la bibliografía [251]. En este trabajo, debe considerarse la distribución de la luz dentro del tumor, para evitar sacar conclusiones y predicciones erróneas, respecto al posible éxito del tratamiento.…”

“…En este trabajo, debe considerarse la distribución de la luz dentro del tumor, para evitar sacar conclusiones y predicciones erróneas, respecto al posible éxito del tratamiento. Además, es importante colocar la fuente de luz perpendicular al tumor, para minimizar errores que alteran la fluencia de fotones dentro del tumor, pues si el ángulo de incidencia es menor de 15 • en el tratamiento con TFD, no es necesario ajustar el ángulo de incidencia [251]. Una correlación plausible entre fluorescencia y la concentración de m-THPC debe depender de las propiedades ópticas del tejido.…”