Instrument for scanning the angular variation of irradiance in ultraviolet phototherapy cabinets

Iron-based radiochromic systems for UV dosimetry applications

Phototherapy treatment using ultraviolet (UV) A and B light sources has long existed as a treatment option for various skin conditions. Quality control for phototherapy treatment recommended by the British Association of Dermatologists and British Photodermatology Group generally focused on instrumentation-based dosimetry measurements. The purpose of this study was to present an alternative, easily prepared dosimeter system for the measurement of UV dose and as a simple quality assurance technique for phototherapy treatments. Five different UVA-sensitive radiochromic dosimeter formulations were investigated and responded with a measurable and visible optical change both in solution and in gel form. Iron(III) reduction reaction formulations were found to be more sensitive to UVA compared to iron(II) oxidation formulations. One iron(III) reduction formulation was found to be especially promising due to its sensitivity to UVA dose, ease of production, and linear response up to a saturation point.

Ultraviolet phototherapy: review of options for cabin dosimetry and operation

Ultraviolet (UV) treatment dose is determined by the length of time that a patient spends in a phototherapy cabin. The output from UV fluorescent lamps declines with use and a method is needed to compensate for the change in irradiance and to identify and replace any lamps that fail. The decline in lamp output with age and the magnitudes of localized areas of low irradiance resulting from failed lamps have been measured and results used to assess different approaches to lamp replacement. In current cabin models, single failed lamps give cold spots with 7%-12% lower irradiances and replacements with new lamps give 3%-6% higher localized irradiances. However, cold spots with 30% lower irradiances may result from lamp failures in some older dual UVA/TL01 lamp cabins. The use of internal cabin detectors that can be employed to compensate for changes in irradiance level is beneficial. Cabins having pairs of internal detectors provide a reasonable reflection of the changes in irradiance that occur and the position of the patient in the cabin should not affect the treatment dose by more than +/-6%. There should be a robust system to identify and replace failed lamps to minimize the risk of erythema.

A study of the correction factor for ultraviolet phototherapy dose measurements made by the indirect method

BACKGROUND

Optimization of ultraviolet (UV) phototherapy for treatment of psoriasis and other skin conditions requires accurate dosimetry. One factor involved in whole body treatments is the correction that needs to be applied to radiometer measurements of irradiance made remotely without a person in the phototherapy cabin.

OBJECTIVES

To evaluate the correction factor for cabins of different design and to consider whether different factors should be used for different phototherapy cabins and radiometers.

METHODS

An automated UV dosimetry system capable of recording irradiances at positions around the circumference of a circle equating to a human trunk has been developed. The system has been combined with a phantom to derive values for the ratio between irradiance measurements made by the direct method with a person in a cabin, and indirect measurements recorded remotely. In addition, values for the ratio in UVA cabins have been derived from comparisons between measurements made directly by persons in a cabin and indirect measurements.

RESULTS

Variations in direct to indirect ratio (DIR) with cabin type were less than between individual sets of measurements. The mean DIR obtained for cabins with TL01 lamps was 0.85 +/- 0.02, while that for UVA cabins was 0.80 +/- 0.05. The DIR for dual lamp (TL01/UVA) cabins, when TL01 lamps were illuminated, was higher (0.92).

CONCLUSIONS

The DIR should be applied to any measurements made using radiometers without a person or equivalent phantom in a cabin. It is proposed that standard values are appropriate for groups of cabins with a single type of lamp and similar reflectors.