Measurement of patient dose in ultraviolet therapy using a phantom

A phantom was developed as a reproducible means of measuring the irradiance in an occupied ultraviolet cabin, by placing the phantom, or replica person, in the cabin, obviating the need for human exposure. The contributions to the patient irradiance measured in the cabin were investigated, looking in particular at the effect of the reflectors. Radiation undergoing single reflection was seen to contribute to a greater extent than multiple reflections. Placing an object in the cabin reduces the measured irradiance due to the blocking of multiple reflections, but variation in the exact shape and size of the object has less effect, which is useful as patients are of all shapes and sizes and a representative phantom was to be developed. The phantom was made of expanded polystyrene blocks with an embedded probe. Measurements were made to verify the equivalence of human and phantom cabin occupancy. It was found that the irradiance measured with the phantom in the cabin lies within the values measured with human occupancy.