Non-ionizing, laser radiation in Theranostics: The need for dosimetry and the role of Medical Physics.

The discovery of coherent laser light in 1960 shifted and expanded the biomedical applications of radiation to the non-ionizing part of the electromagnetic spectrum. As in the case of ionizing radiation, but considering the laser specific features, the effective, safe and ethically acceptable use of biomedical laser technology requires interdisciplinary collaboration between physicists, engineers and physicians. This should extend at the research, preclinical and clinical level, inspiring at this time the dynamic discipline of Medical Physics in new areas. With this work we aim to introduce the interested reader in the need of dosimetry in medical applications of laser radiation, as this field is still unexplored. After some necessary definitions, we give a brief review of the basic biophysical mechanisms of coherent light-matter interactions. The manuscript focuses on biomedical laser applications in diagnosis and therapy (i.e. in Theranostics). From the vast field of laser theranostic applications we have chosen some experimental and theoretical results - examples of quantification of the laser effect, particularly relevant to soft and hard tissue laser ablation, laser induced photodiagnosis and photodynamic therapy of cancer. These topics intend to highlight the important role of Medical Physicists in the optimization of well-established laser based clinical procedures and mainly emerge the necessity of the relevant dosimetry for each application. Finally, we hope that this effort is going to give food for thought and highlight the importance of deep knowledge of the physics behind some everyday medical applications.

Laser-induced fluorescence and reflectance spectroscopy for the discrimination of basal cell carcinoma from the surrounding normal skin tissue.

The object of this study was to investigate whether laser-induced skin autofluorescence (LIF) and/or light reflectance spectra could provide a useful contrast between basal cell carcinoma (BCC) tissues and the surrounding healthy skin. Unstained human skin samples, excised from humans undergoing biopsy examination, were irradiated with a nitrogen laser (lambda = 337 nm) for excitation of autofluorescence and a tungsten halogen lamp for the reflectance measurements. The ex vivo spectroscopic results were correlated with the histopathology images to distinguish the areas of BCC from those of the surrounding health skin. A simple spectral analysis technique was also applied for better skin diagnosis. In conclusion, it seems that LIF and reflectance spectra could be used to differentiate neoplastic from normal skin tissue using an appropriate classification model analysis.

In vitro fluorescence measurements and Monte Carlo simulation of laser irradiation propagation in porcine skin tissue.

In dermatology, the in vivo spectral fluorescence measurements of human skin can serve as a valuable supplement to standard non-invasive techniques for diagnosing various skin diseases. However, quantitative analysis of the fluorescence spectra is complicated by the fact that skin is a complex multi-layered and inhomogeneous organ, with varied optical properties and biophysical characteristics. In this work, we recorded, in vitro, the laser-induced fluorescence emission signals of healthy porcine skin, one of the animals, which is considered as one of the most common models for investigations related to medical diagnostics of human cutaneous tissues. Differences were observed in the form and intensity of the fluorescence signal of the porcine skin, which can be attributed to the different concentrations of the native fluorophores and the variable physical and biological conditions of the skin tissue. As the light transport in the tissue target is directly influencing the absorption and the fluorescence emission signals, we performed Monte Carlo simulation of the light distribution in a five-layer model of human skin tissue, with a pulsed ultraviolet laser beam.

Laser induced autofluorescence studies of animal skin used in modeling of human cutaneous tissue spectroscopic measurements.

BACKGROUND/PURPOSE: Laser-induced autofluorescence spectroscopy provides excellent possibilities for medical diagnostics of different tissue pathologies including cancer. However, to create the whole picture of pathological changes, investigators collect spectral information from patients in vivo or they study different tumor models to obtain objective information for fluorescent properties of every kind of healthy and diseased tissue. Therefore, it is very important to find the most appropriate, and close to the human skin, animal samples from the fluorescence point of view, which will allow the extrapolation of the animal data to human spectroscopic diagnostics. METHODS: In the present work, we examined the autofluorescence properties of different animal skin tissues, which are considered as the most common skin models. A nitrogen laser was used as an excitation source. Samples of healthy mouse, chicken and pig skin in vivo and/or ex vivo were studied and were compared with results obtained from investigations of healthy human skin in vivo. RESULTS AND CONCLUSION: Specific features of the recorded spectra are discussed and the possible origin of the obtained fluorescence signals is proposed. Quantitative evaluation of data extrapolation for each skin type is also depicted.