An automated dosimetry system for testing whole-body ultraviolet phototherapy cabinets

A new technique is described for automated ultraviolet dosimetry within whole-body phototherapy cabinets. A dual-head detector system has been designed, permitting simultaneous assessment of irradiance levels and radiant intensities from individual lamps. One detector is used in combination with a diffuser/filter system for the measurement of irradiance and the other is mounted at the end of a slit collimator to provide a measurement which can be related to the radiant intensities of the individual lamps. These quantities are derived from 800 separate measurements made during rotation of the detector head around a 360 degrees circle at a fixed height and position within the cabinet under remote computer software control. The device has advantages compared with standard techniques, enabling measurements to be made without the need for a person to be present in the cabinet. A full set of measurements is made with minimal switching of the power supply to the lamps. This simplifies the assessment and reduces the uncertainty from variation in output after the lamps are switched on. Variations in irradiance with orientation for the smaller phototherapy cabinets are clearly demonstrated. Plots of data from the collimated detector show peaks corresponding to the lamps and the surrounding reflectors. The plots enable failed lamps to be detected and peak values can be related to radiant intensities of individual lamps.