The use of diode array spectroradiometers for dosimetry in phototherapy

Abstract

An evaluation of two diode array radiometers, an UV spectroradiometer, Type SC-MP-A, from 4D Controls (Redruth, UK) and an USB2000-UV-VIS spectrometer from Ocean Optics (Duiven, NL), was carried out at the Photobiology Unit, University of Dundee. Three parameters of the instruments' performance were investigated, having been identified as the most likely sources of error in phototherapy dosimetry: (1) calibration, (2) stray light rejection, (3) angular response. An assessment was then made of the reliability of this type of instrument for dosimetry in clinical practice by measurement of a selection of phototherapy sources, in direct comparison with calibrated radiometers. Both instruments were found to have significant stray light levels (SC: 13% and USB: 39%). The use of stray light compensation and a high output calibration source improves accuracy to within acceptable limits. Angular responses were satisfactory: f2 values (+/- 60 degrees) of 5.9% and 7.8% for SC and USB, respectively. The SC spectroradiometer is supplied as a calibrated instrument. Using the supplied calibration resulted in errors in measuring phototherapy sources of up to 44% in UVA. Alternative calibration reduced the error in measuring UVA and UVB sources to within 12%. The USB spectrometer was found to have insufficient responsivity in both UVB and UVA to provide reproducible measurements of most phototherapy sources.

Solar simulated radiation induced cell death depends on spectral distribution and irradiance but not output delivery

“…Each source was sampled using the USB2000 spectrometer with an integration time of 100 ms per scan to achieve maximum signal without saturation and an average of 200 scans to increase the signal to noise ratio (24) . Although the USB2000 has been reported to possess poor stray light rejection (25) , it was also shown that with adequate correction that the levels of stray light could be significantly reduced to less then 1 % at 250 nm (25) . A simple correction analogous to *Corresponding author: alanna.maguire@dit.ie background subtraction was employed in this study where the difference in signal between the blacked out pixels corresponding to 180 nm and at 250 nm, a wavelength at which no signal would be expected, was determined and subtracted at all wavelengths.…”

Study of suitability of AvaSpec array spectrometer for solar UV field measurements

“…In most cases the Brewer spectrometers and other expensive spectrum scanning instruments are used. As an alternative, the advancement of technology has made available the compact and simple single-monochromator array spectrometers (JETI Technische Instrumente GmbH, 2005;Oliver and Moseley, 2002;Ylianttila et al, 2005). However, the limited dynamic range and intrinsic stray light problems complicate their use.…”

Guidelines on the measurement of ultraviolet radiation levels in ultraviolet phototherapy: report issued by the British Association of Dermatologists and British Photodermatology Group 2015

“…Evidence of reduced variability in UV radiometer calibrations is seen in intercomparisons from around Europe published in the 1980s, which showed a spread in measured calibration factors of UVA radiometers of 23%, while a more recent study demonstrated only a 6% spread . Finally, there have also been valuable instrumental advances, with the introduction of compact solid‐state spectroradiometers making it much easier than previously to capture spectral information from clinical UVR equipment …”