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Abstract
Purpose: The temporal and spatial formation of the temperature field and its changes during/upon water-filtered infrared-A (wIRA)-irradiation in porcine skin and subcutis were investigated in vivo in order to get a detailed physical basis for thermotherapy of superficial tumors and infections caused by thermosensitive microbial pathogens (e.g., Mycobacterium ulcerans causing Buruli ulcer).Methods: Local wIRA-hyperthermia was performed in 11 anesthetized piglets using 85.0 mW cm−2, 103.2 mW cm−2 and 126.5 mW cm−2, respectively. Invasive temperature measurements were carried out simultaneously in 1-min intervals using eight fiber-optical probes at different tissue depths between 2 and 20 mm, and by an IR thermometer at the skin surface.Results: Tissue temperature distribution depended on incident irradiance, exposure time, tissue depths and individual ‘physiologies’ of the animals. Temperature maxima were found at depths between 4 and 7 mm, exceeding skin surface temperatures by about 1–2 K. Tissue temperatures above 37 °C, necessary to eradicate M. ulcerans at depths <20 mm, were reached reliably.Conclusions: wIRA-hyperthermia may be considered as a novel therapeutic option for treatment of local skin infections caused by thermosensitive pathogens (e.g., in Buruli ulcer). To ensure temperatures required for heat treatment of superficial tumors deeper than 4 mm, the incident irradiance needed can be controlled either by (a) invasive temperature measurements or (b) control of skin surface temperature and considering possible temperature increases up to 1–2 K in underlying tissue.
Highlights
Water-filtered infrared-A radiation (780–1400 nm) [1] shows a significantly deeper penetration into skin and subcutaneous tissue compared to unfiltered IR-A radiation and both, the middle (IR-B, 1400–3000 nm) and the long-wavelength (IR-C, 3000 nm–1 mm) infrared radiation [2,3]
This property causes basic differences concerning tissue heating as compared to conventional heat sources used in thermotherapy such as unfiltered IR-A, IR-B, IR-C, heating packs, hotwater baths and heated air/vapor flows reported by various authors
The complete documentation of surface and tissue temperature data sets measured as a function of time and depth before, during and after water-filtered infrared-A (wIRA)-irradiation of each piglet is presented in the Supplemental Material
Summary
Water-filtered infrared-A (wIRA) radiation (780–1400 nm) [1] shows a significantly deeper penetration into skin and subcutaneous tissue compared to unfiltered IR-A radiation and both, the middle (IR-B, 1400–3000 nm) and the long-wavelength (IR-C, 3000 nm–1 mm) infrared radiation [2,3]. This property causes basic differences concerning tissue heating as compared to conventional heat sources used in thermotherapy such as unfiltered IR-A, IR-B, IR-C, heating packs, hotwater baths and heated air/vapor flows reported by various authors. Piazena et al [6] and Vaupel et al [25] provided related physical and photobiological basics with reference to the ESHO quality assurance guidelines for superficial hyperthermia in oncology [26,27]
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