Guidelines on the measurement of ultraviolet radiation levels in ultraviolet phototherapy: report issued by the British Association of Dermatologists and British Photodermatology Group 2015
Authors: H. Moseley, D. Allan, H. Amatiello, A. Coleman, H. du Peloux Menagé, C. Edwards, L.S. Exton, J. Ferguson, T. Garibaldinos, C. Martin, M.F. Mohd Mustapa, P.M. McHenry, M. Griffiths, D.A. Buckley, I. Nasr, V.J. Swale, C.E. Duarte Williamson, T.A. Leslie, E. Mallon, K. Towers, C. Saunders, A.G. Brain
Journal: British Journal of Dermatology (2015)

The overall objective of the guideline is to provide up-to-date, evidence-based recommendations for the dosimetry and calibration of ultraviolet (UV) radiation (UVR) therapy. The document aims to: (i) offer an appraisal of all relevant literature, focusing on any key developments; (ii) address important, practical clinical questions relating to the primary guideline objective, that is, accurate measurement, equipment variables, and human variables; (iii) provide guideline recommendations and, where appropriate, discuss health economic implications; and (iv) discuss potential developments and future directions The guideline is presented as a detailed review with highlighted recommendations for practical use in the clinic [see section 18·0, in addition to a patient information leaflet on phototherapy, which is available on the website of the British Association of Dermatologists (BAD): www.bad.org.uk]. The guideline development group consisted of clinical scientists, consultant dermatologists and a nurse practitioner. The draft document was circulated for comments to the BAD membership, the British Photodermatology Group (BPG) membership, the British Dermatological Nursing Group, the Primary Care Dermatological Society, the Institute of Physics and Engineering in Medicine, the Psoriasis Association, the Psoriasis and Psoriatic Arthritis Alliance, and a patient, and peer-reviewed by the Clinical Standards Unit of the BAD (consisting of the Therapy and Guidelines Subcommittee) prior to publication. This set of guidelines has been developed using the BAD's recommended methodology,1 and with reference to the Appraisal of Guidelines Research and Evaluation II instrument (www.agreetrust.org).2 Recommendations were developed for implementation in the National Health Service using a process of considered judgement based on the evidence. Clinical trials are not appropriate for this guideline. The recommendations made are those that are currently considered best practice but will be modified at intervals in the light of new evidence. The structure of the 2002 guidelines was discussed and re-evaluated,3 with headings and subheadings decided; different co-authors were allocated separate subsections. PubMed, MEDLINE and Embase were searched up to December 2014; search terms and strategies are detailed as in Appendix S1 (see Supporting Information). Additional relevant references were also isolated from citations in the reviewed literature. The results were split into two and, working in quartets, each group of co-authors screened a set of identified titles/abstracts, and those relevant for first-round inclusion were selected for further scrutiny. The authors then reviewed the abstracts for the shortlisted references with reference to their allocated subsection and the full papers of relevant material were obtained. Each co-author then performed a detailed appraisal of the selected literature, and all drafted subsections were subsequently collated and edited to produce the final guideline. This document has been prepared on behalf of the BAD and is based on the best data available when the document was prepared. It is recognized that under certain conditions it may be necessary to deviate from the guidelines and that the results of future studies may require some of the recommendations herein to be changed. Failure to adhere to these guidelines should not necessarily be considered negligent, nor should adherence to these recommendations constitute a defence against a claim of negligence. Limiting the review to English-language articles was a pragmatic decision but the authors recognize this may exclude some important information published in other languages. The proposed revision date for this set of recommendations is scheduled for 2020; where necessary, important interim changes will be updated on the BAD website. The key contribution of the medical physics community to the development of psoralen combined with UVA photochemotherapy (PUVA) and UVB phototherapy since its first use in the U.K. in the 1970s has been to ensure that the dose of UVR is administered quantitatively rather than qualitatively.4 In 2002 the BPG published dosimetry guidelines that codified the experience gained in how best to ensure the phototherapy dose is accurately measured.3 In the decade since, there have been some significant advances in technology for the delivery and measurement of phototherapy dose, as well as changes in regulatory and clinical governance environments affecting phototherapy dosimetry.5, 6 These guidelines take account of the advances and are intended to update and replace those previously published.3 The term ‘dose’ in the context of clinical phototherapy is taken to be the time integral of the irradiance of the therapeutic radiation over the time during which the skin is exposed.7 The irradiance at the skin surface is typically measured in units of power per unit area [e.g. milliwatts per cm2 (mW cm−2)] so that, for an exposure time in seconds, the dose takes on units of energy per unit area [e.g. joules per cm2 (J cm−2)]. Confining the definition of dose to that delivered at the skin surface rather than at depth in a volume of tissue, as is common in experimental photobiology, has considerable advantages, not least being its relative ease and reproducibility of measurement.7 The early protagonists of UV therapy stressed the importance of careful dosimetry, particularly where patients needed to continue treatment on different irradiation units in the same or different centres,8, 9 and the need to base starting doses on either skin type or the results of phototesting.10 Similarly, it was recognized that careful detector calibration was needed to measure the output of different irradiation units having different spectral emission characteristics.11, 12 Despite the early awareness of the need for accurate dosimetry in PUVA, intercomparisons of UVA dosimetry in the U.K. found wide variability in practices and in the accuracy of UVA measurement.13-15 Incorrect use of radiometers and poor calibration was found to result in recorded irradiance values that were between 0·5- and 1·5-fold the true value. In a survey of 115 UVB phototherapy centres in the U.K. in 1994,16 it was noted that the overwhelming majority prescribed UVB by exposure time rather than in radiometric units. This is no longer considered good practice unless there is a calibration factor available to users that allows a conversion to dose, so that the dose, rather than a time, can be recorded in the patient's notes. The erythemal sensitivity of skin changes very rapidly with wavelength in the UVB waveband; at 300 nm the skin is 100 times more sensitive than at 320 nm. Thus, the dose of UVB radiation from a particular lamp necessary to produce a given degree of erythema is markedly dependent on its spectral emission. The need for accurate UVB dosimetry became particularly apparent in the 1990s with the introduction of narrowband UVB (NB-UVB) treatment and the requirement to compare the effectiveness and safety of this new treatment with older broadband UVB (BB-UVB) treatments.17 The short wavelengths found in BB-UVB are more likely to cause burning than NB-UVB. NB-UVB treatment has now virtually replaced BB-UVB. Guidelines regarding the clinical use of phototherapy have been developed.18, 19 The calibration of UV radiometers for phototherapy has also improved markedly in the last decade with the introduction of traceability to national irradiance standards via the National Measurement System (NMS).20, 21 This makes it possible to ensure that the irradiance measured in one centre is comparable with that measured at other centres using differently calibrated radiometers. 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%,14 while a more recent study demonstrated only a 6% spread.22 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.23, 24 The role of phototherapy has recently been re-evaluated in response to the revolution in biological therapies for psoriasis.25, 26 Despite the benefits of these therapies that target specific components of the immune system, it seems clear that phototherapy will remain a cornerstone in the management of psoriasis, as well as in nonpsoriatic skin conditions, because of its acknowledged efficacy, its reasonable financial cost, its compatibility with other therapies and its historically proven utility. See Appendix 1 for a glossary of terms; see Appendix 2 for a description of the level of evidence; see Appendix 3 for a description of the strength of recommendations. Accurate and reproducible dosimetry is considered important in phototherapy, not only to ensure that patients can be treated consistently in the same centre or be transferred between centres, but also to ensure that a patient's absolute cumulative dose (in J cm−2) can be accurately recorded to aid the management of long-term skin cancer risks (Ling et al., British Association of Dermatologists and British Photodermatology Group draft 2014 guidelines for the safe and effective use of psoralen combined with ultraviolet A therapy).27 A dose measurement accuracy of 10% is generally considered adequate for clinical phototherapy.28, 29 In treatment cabins, for example, patient positioning and the nonuniformity of irradiation of the skin due to its curvature may be > 15%.11 Similarly, differences in the output of the different lamps in the array can be 15% and fluctuations in the output of lamps during treatment can be as much as 10%.30 Modern solid-state UV filter radiometers can make highly reproducible measurements with sequential readings of a stable source varying by < 1%. However, a meter may provide a reproducible reading without the reading being accurate in terms of the absolute dose (in J cm−2). Indeed, it is difficult in practice to calibrate a field UV meter with an accuracy much better than 10%.28, 29 The UV meter calibration uncertainties quoted by those U.K. laboratories operating to the standard ISO 17025 are typically of the order of 10% and are therefore adequate for most clinical UV dosimetry.31 As the calibration factors provided are specific to radiometers being used with sources having a particular spectral output, the main issue for users is to ensure that they request and use the appropriate calibration factor. Users also need to be aware that UV meter degradation can cause the meter to drift out of calibration, so regular calibration is required. Although the introduction of traceable dosimetry has been an important step in improving dosimetry accuracy in phototherapy centres, there remain areas of concern, particularly in the variability of dosimetry for NB-UVB phototherapy.28 Large discrepancies in dosimetry between centres seem likely to be owing, at least in part, to poor matching of the cosine directional response of UV radiometers and unresolved calibration issues where the spectral output of a source varies rapidly with wavelength.32, 33 UVR is carcinogenic; therefore, it is important that exposure of staff and members of the public is within acceptable limits. Any potential exposure to UVR should be covered by a suitable and sufficient prior risk assessment that is subject to regular review. Any necessary control measures to reduce the risks associated with working with UVR should be documented in this risk assessment and be put in place. Staff should be trained to an appropriate level and be made aware of any control measures that may be required such as the use of personal protective equipment (PPE) or high-factor sunscreen. Staff should be aware that there may be scattered UVR from ceilings or walls around the cabin when working in the general vicinity of cabin and partial-body irradiation equipment. Exposure to these devices and to the environmental scatter is generally low but an assessment of the level of environmental UVR should be carried out in line with the Control of Artificial Optical Radiation at Work Regulations 2010.5 Such measurements could be carried out by a local medical physics department or others with the expertise to make such measurements. Measured irradiances should be compared with the legal limits laid down in these regulations, with due consideration made to occupancy and workload factors. There may be additional control measures that are required to reduce environmental UVR, such as the use of curtains and drapes. A suitable assessment of risk should include the measurement of environmental UVR levels to which staff are exposed and the identification of appropriate control measures. Environmental UVR levels should be within the maximum permissible levels proscribed in the Control of Artificial Optical Radiation at Work Regulations 2010. Delivering safe care is a prime consideration for all healthcare workers. Legal claims can help highlight aspects of practice prone to mishap or dispute. Although dermatology as a whole is a low-risk specialty, phototherapy has been highlighted as a vulnerable area, with a significant number of claims resulting from overexposure to UVR.34-36 The potential long-term risk of skin cancer with cumulative phototherapy treatment is also an important clinical governance consideration.37 Audits of phototherapy provision have revealed great variation in the quality of service provided between centres. The BAD has recently recommended minimum service standards for phototherapy and offers supporting guidance to inform service.38 These include a phototherapy service review toolkit to provide phototherapy units with a framework for assessing their service against these minimum standards.39 Achieving a consistent standard for safe and effective phototherapy service provision across the U.K. should follow. Most UV phototherapy treatments are delivered in hospital or clinic settings. As many patients have large proportions of their skin surface needing treatment, whole-body phototherapy cabins where the patient is surrounded on all sides by banks of UV lamps are the equipment of choice for most treatments. The last few decades have seen an increase in the use of NB-UVB phototherapy, with an accompanying decline in PUVA and BB-UVB treatments.19 The use of whole-body UVA1 phototherapy has also become more common recently. For areas with more remote populations without easy access to phototherapy centres, the use of home phototherapy units has proved popular and cost-effective in enabling self-administration of treatment.40, 41 Whole-body home phototherapy units are more usually an open single bank of lamps rather than an enclosed whole-body cabin. Any one treatment session therefore consists of four separate exposures: to the front and back, and to the left and right sides. Partial-body irradiation equipment is also widely used for both self-administered and clinic-based phototherapy. A small bank of lamps in either a flat or curved array is suitable for treating hands, feet or lower limbs. Smaller, hand-held devices are often used for less accessible treatment sites such as the scalp. All such units should be operated in areas where access can be controlled to avoid unnecessary exposure to the beam. In the case of the patient, untreated skin and eyes should be protected as necessary by means of clothes, drapes, goggles or face shields. Equipment management issues associated with whole-body treatment cabins are considered in the following subsections. Whole-body cabins are typically more sophisticated in operation than partial-body irradiation units, with many having inbuilt automated dosimetry systems. They also present a greater potential hazard because of the higher UV irradiances they generate and the fact that a larger area of the patient's skin is typically irradiated. However, many of the UV dosimetry principles discussed will apply equally to the smaller partial-body units. Different models of whole-body phototherapy cabins contain differing numbers of lamps – 24, 26, 40 or 48 lamps being the more common. The UV irradiance comprises UVR emitted directly from the lamps and UVR reflected from polished surfaces to the side and rear of the lamps. The angles of these reflectors have a significant influence on the overall cabin efficiency.42, 43 The reflectivity coefficients of different materials used for the reflectors by the various cabin manufacturers can also vary significantly.42 Increasing the number of lamps within a cabin beyond a certain point does not necessarily increase the irradiance proportionately. A recent study compared the outputs from two sets of cabins, with similar dimensions, differing only in the numbers of lamps, from the same manufacturer.43, 44 Cabins with 24 lamps gave irradiances that were only 11% less than those with 40 lamps. It was concluded that the smaller reflector angle in the 40-lamp cabins reduced the useful output per lamp by a third. The uniformity of illumination, which is the most important factor for treatment delivery, was found to be similar in the cabins with 24 and 40 lamps. Cabins that only employed a simple, flat reflector behind the lamps had lower efficiencies. Irradiances in the range of 6–8 mW cm−2 are generally required for NB-UVB therapy and in the range of 10–14 mW cm−2 for UVA therapy. Therefore, cabins with > 24–30 lamps may offer little advantage in terms of treatment times. To allow treatment with either spectrum, some cabins have a combination of UVA and UVB fluorescent lamps that are operated using separate controllers. These cabins hold either 16 UVB and 32 UVA lamps or 13 UVB and 27 UVA lamps. Although these cabins save space, the overall cabin irradiance of each modality is proportionally reduced and, consequently, treatment times are increased. There is also the risk of selecting the wrong treatment mode, although internal dosimetry systems, if these are used, will typically include exposure limits that prevent the longer UVA exposure times being given by the UVB lamps. Therefore, this type of cabin is not generally recommended. If it is necessary to have a dual cabin because of space limitations, extreme care must be exercised when entering the lamp type and treatment dose. The number of lamps in a cabin may affect installation and running costs. Cabins with fewer lamps require less complex electrical supply arrangements, whereas those with 40 or more fluorescent lamps typically require a three-phase electricity supply that may not be readily available on some sites. They also produce more heat and therefore efficient air conditioning systems are required to maintain patient comfort. Exposure control in whole-body phototherapy cabins can be either time-mode or dose-mode. Some cabin designs can be operated in only one of these modes, while others offer a choice of either mode of operation. Depending on user preferences, the choice of control modes may be an important consideration when acquiring a new treatment cabin. Time-mode may be the only control method available on older cabins. The user sets an exposure time corresponding to the prescribed treatment dose, and based on prior irradiance measurements. The cabin's inbuilt electronic timer then controls the exposure; there is no automatic allowance for differences in patient size or variations in the cabin irradiance.30 To maintain accuracy, a programme of regular irradiance calibration tests is necessary, typically after 50 h of use and repeated at least every 4 months. Most currently available cabins are capable of dose-mode control. The cabin is fitted with internal detectors that measure the internal irradiance in real time during treatment. The operator sets the required dose on the controls and starts the treatment. The control system electronically integrates the continuous irradiance reading, and the exposure is automatically terminated when the set dose is reached. Dose-mode operation can also compensate automatically for fluctuations in irradiance arising both during individual treatments and over a full clinic session. More consistent doses may then result. The effectiveness and accuracy of inbuilt sensor systems is dependent on detector position and cabin geometry. Some early designs have been prone to give misleading readings (Moseley, personal communication).30, 45 Especially problematic are types reliant on monitoring a small number of lamps.46 More recent types compensate reasonably well for differences in the amount of shielding of the fluorescent tubes by patients of differing sizes.29, 47, 48 However, it should be recognized that internal dosimeters monitor the UV that is reflected from a relatively small area of skin and do not measure the average irradiance to the whole patient. Internal detectors may also be sensitive to the patient's relative position within the cabin. If a patient moves off centre, the detected cabin irradiance level will alter as the different banks of lamps within the cabin will contribute more or less to the total irradiance. This may cause some variation in the patient's actual received dose, leading to either under- or overdosing. It has been shown that cabins fitted with a pair of detectors are less susceptible to this type of dose error than cabins with single detectors.30, 48 When inbuilt, dose-mode sensors are fitted, users should not assume that the dose displayed on the cabin's control panel is correct. A programme of regular calibration checking of any inbuilt metering system should be in place to ensure accuracy and to guard against malfunctions. To avoid confusion, this should be done even if the cabin is usually operated in time mode. Should a patient fall against unprotected lamps inside a phototherapy cabin, there is a high risk of laceration. Many older phototherapy cabins either had no protection at all against this or had relatively open metal grilles. Now, full acrylic guards over the lamps are generally fitted as standard. Users of phototherapy cabins without guards in place were required to consider retrofitting them following the publication of the medical device alert (MDA/2003/006) issued by the Medical Devices Agency (now the Medicines and Healthcare products Regulatory Agency) in 2003 and the associated Scottish Safety Action Notice in 2003 [(SAN(SC)03/14].49, 50 Improved ventilation within cabins has also enhanced safety by increasing patient comfort and making it less likely that they will become faint and stumble. Through better-fitting doors and UV-opaque viewing windows, newer cabin designs generally have lower UV leakage. Moreover, most cabin doors are now interlocked so that the exposure will stop immediately if a patient pushes against the door. Interlocked patient-actuated pull cords fitted in some cabin designs have a similar safety function. It may be acceptable to continue to use older cabins without such safety features provided an assessment is made of their safety in the light of current regulatory requirements and best practice guidance. Regular cleaning of cabins is imperative for infection control. Accumulated skin flakes and dust on lamps can also degrade the cabin output and internal dosimetry systems. Thorough cleaning of cabins – screens taken out and cleaned, reflectors and lamps wiped, and accumulated dust removed – can increase the output of cabins by up to 20% (Amatiello, personal communication). Although concerns have been raised about the safety of patients with artificial implanted devices, a recent investigation in two phototherapy cubicles demonstrated that the cabinets were safe for patients fitted with electrical implanted devices, such as pacemakers.51 The absolute output declines as lamps age. For Philips type TL-01 100 W fluorescent tubes, this decline is rapid over the first 200 operating hours, dropping to 60–70% of the initial intensity, before maintaining a relatively constant output until lamp failure. There is a large variation in operating life depending upon local circumstances: in one study, mean ± SD lamp lifetime was observed to be 470 ± 170 h.30 When lamps fail, ‘cold spots’, or areas of lower localized irradiance, are formed within the overall irradiance distribution, thereby underdosing an area of the patient. New tubes have higher irradiances and so create ‘hot spots’ or areas of higher localized irradiance. For cabins of the size supplied by most manufacturers, single-lamp failures give cold spots with 7–12% lower irradiances, and replacement with a new lamp gives hot spots of 3–6%. If failed lamps are replaced promptly, localized patient erythema is unlikely. However, in cabins with fewer lamps, where each lamp contributes more to the overall irradiance, and in smaller cabins where the contribution to irradiance from individual lamps is more localized, irradiance may be some 30% lower in cold spots from single-lamp failures. This effect is particularly important in dual UVA/NB-UVB cabins as these have fewer lamps of each type, meaning the impact of a failed lamp is greater. An added complication is that failed lamps are more difficult to identify among lamps of the other type that are not illuminated.30 A robust system to identify and replace failed lamps is therefore required. Replacement of lamps should be carried out in accordance with an agreed policy that is known and understood by the end-users. One option is to replace all lamps when treatment times become unacceptably long; an alternative strategy is to replace those lamps showing a low output so that irradiance in the cabin is kept constant, for example within 10–20% of a desired figure. To avoid accidental treatment with the wrong UV spectrum, it is critical that the correct fluorescent tubes are fitted in the cabin. Some suppliers label NB-UVB tubes with blue and red stickers for easy identification but this helpful practice is not a requirement. This means that there remains a risk of an unlabelled NB-UVB tube being fitted in to a UVA cabin, or vice versa, with potentially serious clinical consequences. Recommendations concerning identification have been made in the 2012 Estates and Facilities Alert (EFA/2012/002).52 Consider uniformity of dose distribution, treatment times, control mode options and installation implications when selecting whole-body cabins. Cabins fitted with tubes providing identical spectral output are recommended over cabins that can be switched to operate two (or more) different spectral outputs. The use of cabins with dosimetry systems providing a biologically weighted dose are not recommended. Regular measurements using a calibrated UV radiometer should be made in order to assess the irradiance to which patients are exposed by phototherapy equipment and to check the accuracy of any dosimetry systems that are incorporated within the equipment. An infection control and hygiene policy should be in place to ensure adequate cleaning of equipment and other surfaces in phototherapy areas. A lamp replacement policy should be in place to ensure that failed or low-output lamps are replaced with lamps of the correct type, and that localized areas of low or high irradiance are avoided. Most UV sources for phototherapy are low-pressure, mercury vapour fluorescent lamps (Fig. 1). See elsewhere for a comprehensive description of optical radiation sources in healthcare.53 NB-UVB is provided by Philips TL-01 lamps with peak output at 311 nm, or Arimed 311 lamps with a slightly longer wavelength peak at 313 nm. Both of these are within the action spectrum for the clearance of psoriasis established by Parrish and Jaenicke,54 but the Arimed 311 has slightly more energy in the lower, more erythemogenic region below 310 nm. Philips supply the same phosphor in 9 W bi-pin and 36 W four-pin compact fluorescent tube format, and in 20 W (0·6 m), 40 W (1·2 m), 100 W (1·8 m) and the newer 120 W (2 m) straight-tube format. BB-UVB lamps emit energies from UVC through to UVA, with peak energy in UVB. Waldmann UV6 and UV21, and Philips TL-12 emit their main energy between 280 nm and 360 nm, with a maximum at 320 nm. They emit wavelengths outside the action spectrum for the clearance of psoriasis so are more erythemogenic than NB-UVB lamps. Their use has declined significantly since the introduction of NB-UVB lamps. PUVA uses BB-UVA lamps that emit over the whole of the UVA spectrum (315–400 nm, peak 350 nm). Lamps manufactured by Philips are labelled as tanning products in the Cleo range (‘Cleo Performance’ tubes are often supplied for PUVA). There are many Cleo lamps, and recently the ‘Cleo Natural’ lamp has been introduced, which has a higher UVB content. They are also supplied as ‘PUVA lamps’, and are available in similar size and wattage options as described above for NB-UVB lamps. Some UVA lamps have an inbuilt reflector to increase the irradiance; these are designated ‘R-UVA’. There is some evidence for the effectiveness of long-wave UVA1 (340–400 nm) for phototherapy. Fluorescent lamps of the Philips TL-10 phosphor are available for populating conventional phototherapy cabins. This is a NB-UVA lamp with emission between 350 nm to 400 nm, peaking at around 370 nm. Other phototherapy sources include medium-pressure metal halide lamps (iron or cobalt halides are common). These emit broadly across the UV and visible spectra, so are almost exclusively used with filters to shape the output spectrum. They are available in power ratings up to 2–3 kW, so are used in UVA1 phototherapy units with output irradiances in the range of 90–130 mW cm−2. Skin type and habits affecting routine UV exposure together determine the UV dose that the skin can endure without an adverse reaction. The choice of irr