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Photodynamic therapy of melanoma. Monte Carlo modeling of light transport in human pigmented skin

Matuszak Z.

Bio-Algorithms and Med-Systems

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2011

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Vol. 7, no. 2

85--93

EN

Among many available methods used in clinical practice to treat cancer tissues, Photodynamic therapy (PDT) is a relatively new tool. PDT is an enhancement of chemotherapy. To destroy cancerous tissue, photosensitizer (PS), oxygen (O2) and light - three crucial elements of PDT - have to work together to produce sufficiently high concentration of cytotoxic reagents, reactive species of oxygen (ROS), mainly singlet oxygen 1O2. To effectively generate 1O2, light intensity needed for the activation PS should achieve appropriate value in the place of the location of PS within the cancerous lesion. In pigmented cancers amount of melanin is larger than in normal tissues due to proliferation of melanoma cells. Melanin strongly absorbs light and attenuates its intensity. To investigate the influence of melanin on PDT efficiency, a seven-layer computer skin model was proposed and tentatively examined in this work. Influence of melanin on light intensity distribution was simulated with Monte Carlo method. For some fluence rate values (50,100,150 and 200 mWcm-2) the computer simulations of PDT effect using parameters of porphyrin photosensitizer (tritiolyloporphyrin, λex=650 nm) and kinetic schema of PDT based on Jablonski diagram were analyzed. Simulations have shown that fluence rate values strongly modify efficiency of therapy and in the case of low fluence rate values deeper laying cancerous cell would not be killed due to too low 1O2 production. Additionally it was shown that the problem of estimation of melanin content in tissue can be solved by measurement of diffuse reflectance of skin. The possibilities of further development of the model were also briefly discussed.

2

Correction of anisotropy coefficient in original Henyey Greenstein phase function for Monte Carlo simulations of light transport in tissue

Żołek N. S., Wojtkiewicz S., Liebert A.

Biocybernetics and Biomedical Engineering

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2008

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Vol. 28, no. 4

59-73

EN

In this paper, two different methods for calculation of polar deflection angle are compared. The scattering angle is defined by numerical inversion of cumulative distribution of the original Henyey-Greenstein phase function. Results of the Monte Carlo simulations obtained in this manner are compared with results of simulations in which the analytical inversion of the probability density for the cosine of the deflection angle is applied. Investigations are carried out for media with optical properties similar to these typical for living tissues as well for very small source detector separations (50-500 [\mi]m), i.e. in conditions, in which the diffusion theory can not be applied. The distributions of visiting probability of photons penetrating into the semi-infinite medium are obtained for various methods of phase function calculation. It can be observed that the methods of calculation of polar deflection angle influence significantly spatial distributions of reflectance and visiting probability obtained by Monte Carlo simulations. The approximated transformation of the anisotropy coefficient used in simulations carried out with the use of the original Henyey-Greenstein function to effective anisotropy coefficient is presented; that makes possible comparisons of the results of Monte Carlo simulations obtained by using different methods.

3

Optymalizacja kodu Monte Carlo do symulacji czasu przelotu fotonów w strukturach tkankowych

Żółek N. S., Liebert A., Maniewski R.

Bio-Algorithms and Med-Systems

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2005

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Vol. 1, no. 1/2

277--280

PL

Symulacje Monte Carlo są często wykorzystywane w modelowaniu transportu światła w strukturach optycznie mętnych. Pozwalają uzyskać dokładny opis rozchodzenia się światła, ale wymagają dużej mocy obliczeniowej. Najbardziej czasochłonnymi operacjami podczas symulacji są: obliczanie wartości funkcji logarytmicznej i trygonometrycznej oraz generowanie liczb pseudolosowych. W tym artykule została przedstawiona weryfikacja i porównanie metody Monte Carlo wykorzystującej aproksymację funkcji logarytmicznej i trygonometrycznej z metodą klasyczną (z dokładnym obliczaniem logarytmu i funkcji cosinus) i z rozwiązaniami równania dyfuzji dla struktur jednorodnych.

EN

Monte Carlo simulations are frequently used in modeling of light transport in turbid media. They allow precise description of light transport, but require long computation time. Logarithmic and trigonometric functions evaluation, and generation of pseudorandom numbers are main-time consuming procedures in Monte Carlo calculations of light transport. In this paper, parallel Monte Carlo method with approximated logarithmic and trigonometric functions is analyzed, verified, and compared to the original one (with exact computation of logarithm and cosine functions) and with solution of diffusion equation for homogeneous media.

4

ARTHELIO - energetycznie zoptymalizowany system oświetleniowy

Rosemann A.

Przegląd Elektrotechniczny

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2004

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R. 80, nr 5

428-430

PL

Zademonstrowano i przetestowano na dwóch prototypowych instalacjach możliwość wykorzystania do celów oświetleniowych połączenia światła sztucznego z bezpośrednim światłem słonecznym. Głównym celem projektu było oświetlenie stref wewnątrz budynku pozbawionych światła naturalnego lub o jego ograniczonym dostępie. Transport światła, a także jego emisja na całej długości instalacji, odbywał się za pomocą światłowodów rurowych (ang. light pipe, niem. Hohllichtleiter).

EN

Two prototype of lighting system utilizing natural solar light have been demonstrated. This system have been used to lighting of internal (without windows) rooms in the buildings. To transport of the light pipe was used.