PD19 Phototherapy narrowband ultraviolet minimal erythema dose testing: recommendations for handheld minimal erythema dose units

Abstract

Handheld minimal erythema dose (MED) testers provide a convenient and reproducible alternative to conventional panel-based testing; however, their irradiance output is influenced by temperature, warm-up time, aperture position and device design. The BAD recommends that MED testing is performed prior to commencing a course of ultraviolet phototherapy and that this forms part of a high-quality clinical service. A national survey of MED practice across the UK and Ireland was undertaken in 2024. The findings demonstrated that 90% of centres now performing MED testing use small handheld testers. The findings from the survey also demonstrated that there was a wide variation in testing and clinical protocols across the UK and Ireland. The purpose of this work was to develop an agreed set of recommendations on how these devices are tested and used clinically. A full literature review was undertaken and measurements of four different protocols assessed for their suitability and reproducibility. The protocols were assessed independently at three different centres. The literature review identified limitations in existing guidance, particularly with respect to quality assurance and clinical use of handheld MED devices, despite well-established recommendations for spectral matching and traceable dosimetry. Experimental evaluation of the four protocols demonstrated that irradiance and integrated dose varied with operating temperature and cooldown duration. Devices exhibited continued temperature rise even after lamp switch-off, with some surface temperatures exceeding 44 °C, presenting potential risks of reduced dosimetry accuracy and patient discomfort. Protocols incorporating longer cooldown times (≥ 15 min) demonstrated improved repeatability, with maximum deviations from mean integrated dose < 5%, compared with poorer repeatability observed with shorter cooldown periods. Based on survey findings, experimental evaluation and literature review, this work proposes practical standardized recommendations for commissioning, quality assurance testing and clinical use of handheld MED testers.