Effect of wavelength and beam width on penetration in light-tissue interaction using computational methods

Abstract

Penetration depth of ultraviolet, visible light and infrared radiation in biological tissue has not previously been adequately measured. Risk assessment of typical intense pulsed light and laser intensities, spectral characteristics and the subsequent chemical, physiological and psychological effects of such outputs on vital organs as consequence of inappropriate output use are examined. This technical note focuses on wavelength, illumination geometry and skin tone and their effect on the energy density (fluence) distribution within tissue. Monte Carlo modelling is one of the most widely used stochastic methods for the modelling of light transport in turbid biological media such as human skin. Using custom Monte Carlo simulation software of a multi-layered skin model, fluence distributions are produced for various non-ionising radiation combinations. Fluence distributions were analysed using Matlab mathematical software. Penetration depth increases with increasing wavelength with a maximum penetration depth of 5378 μm calculated. The calculations show that a 10-mm beam width produces a fluence level at target depths of 1–3 mm equal to 73–88% (depending on depth) of the fluence level at the same depths produced by an infinitely wide beam of equal incident fluence. Meaning little additional penetration is achieved with larger spot sizes. Fluence distribution within tissue and thus the treatment efficacy depends upon the illumination geometry and wavelength. To optimise therapeutic techniques, light-tissue interactions must be thoroughly understood and can be greatly supported by the use of mathematical modelling techniques.

Light Sources and Dosimetry Techniques for Photodynamic Therapy

“…The absorption wavelength of the photosensitizer must be matched by the wavelength of the light source. Most commonly used photosensitizers have multiple absorption peaks (several Q‐bands in the red (600–700 nm) and the Soret band in the blue (~400 nm)); however, a longer wavelength light source is preferred due to the deeper penetration of the light in tissue which allows treatment of a greater target tissue .…”

Recent Considerations in the Application of RAPTA‐C for Cancer Treatment and Perspectives for Its Combination with Immunotherapies

“…Indeed, the tumor microenvironment including, for example, several biochemical modulating molecules, redox species, different cell types or nutrients, strongly influences treatment responses to chemotherapies and, importantly, the tumor microenvironment and tumor treatment can impact on an immune response. [61] Ru(II) polypyridyl complexes can be reorganized by adding substituents that enhance the light absorption properties [62] that improve their activity. [51,52] KP1019 was initially evaluated on eight patients with solid tumors, applied intravenously to estimate dose escalation with concentrations ranging from 25-600 mg given twice a week over a 3-week period.…”

“…It should be noted that concentrations >400 mg induce a transient green discoloration of the patients' plasma. [34,43,61,62] Notably, the biological properties of RAPTA compounds can be modulated in a systematic way by manipulating the groups attached to the arene ring. [55][56][57][58] The activity of selected Ru(II) polypyridyl complexes is superior to that of some PS in clinical use, for example, antimicrobial agents as porfimer sodium or 5-aminolevulinic acid.…”

Review of human hair optical properties in possible relation to melanoma development

“…Therefore, the refractive index and anisotropy factor of hair are usually assumed and the hair is often simply modeled as a cylinder in the MC simulation. [67][68][69][70] Hair, like skin, can also be damaged by the UV rays. For example, prolonged sun exposure can cause hair to develop split ends, brittleness, dryness, and color fading through photoaging and photodegradation processes.…”

“…The refractive-indexmismatch of hair and skin was taken into consideration in Ash et al's simulation. 69,70 Theoretically, the MC photon simulation in hair requires the knowledge of its absorption coefficient, scattering coefficient, refractive index, and anisotropy factor. However, it is difficult to experimentally determine all the properties, due to the small size of hair.…”