On the validity of using spectrophotometry of cuvettes to provide a dose-response calibration for radiochromic optical computed tomography-based three-dimensional dosimetry

The dose response of materials used in radiochromic three-dimensional (3D) dosimeters is often characterised via spectrophotometry of small cuvette samples as it is less time-consuming and cheaper. However, spatially-resolved dose measurements for clinical purposes are obtained using 3D optical computed tomography (CT). Hence, the link between the method of characterisation and the method for extracting 3D dose information must be established. The aim of this study was to investigate if spectrophotometry-based dose-response characterisation using cuvette-sized samples is valid for calibration of 3D optical CT readout systems using a silicone-based radiochromic dosimeter. Additionally, the uniformity of 3D optical CT dose-response readout of larger samples was investigated. We found the dose response of cuvette-sized samples read out by spectrophotometry to agree with the averaged dose response across cuvette-sized samples read out by optical CT and with the response near the edges of larger samples scanned using the same apparatus. Thus, cuvette-based dose-response spectrophotometry can be used to calibrate 3D optical CT readout using silicone-based radiochromic dosimeters. However, caution should be taken when considering larger samples as they exhibit a gradual radial increase in dose response from the centre and outwards.