Patient UVA dosimetry using Gafchromic film

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There is currently no method to measure the doses received by a patient during PUVA therapy. While some Monte Carlo modelling has been carried out, there is no measured data on the skin dose actually received by the patient. Commercially available electronic detectors are expensive, often only measure instantaneous irradiance rather than exposure values and cannot provide measurement at many different sites at the same time. Measured skin dose will allow further optimisation in the delivery of UVA radiation. This study investigates the use of Gafchromic EBT3 (Ashland, USA) as a patient UVA dosimeter. EBT3 Gafchromic film has been designed by its manufacturers as a tool for radiotherapy dosimetry. However, other studies have shown the film can be used to quantify solar UV dose. The film is easy to use and is minimally inconvenient for the patient. As the film is flat, it mimics skin in a geometry that cannot be matched using electronic detectors and allow simultaneous measurements at many sites. Absorption peaks of the film are located in the visible red region meaning a visual change in film colour will be observed upon sufficient exposure to UVA radiation. Scanning of the film using an Epson V800 scanner and analysis of the images using ImageJ and Microsoft Excel then provides UVA dosimetry information. The film was calibrated against a calibrated UVA radiometer and used in the field to provide an acceptable level of accuracy. The Epson V800 scanner was purchased using the YIG grant received from the IAPM