An investigation of a potential multipurpose readout modality for two and three-dimensional dosimetry using optical computed tomography scanners

Abstract: Radiochromic film, polymer gel and radiochromic plastic are three different kinds of dosimeters developed for radiation therapy. Even though all three types of dosimeters are suitable for optical scanning, the proposed readout method is different for each detector system. In this study, the scanning properties of three optical CT scanners were investigated to determine if they could be developed into multi-purpose scanners, i.e. be used for readout of more than one type of dosimeter. Material and methods: The scanners used were the parallel beam CCD scanner and the fast laser scanner of the University of Surrey, UK and the Octopus IQ scanner located in Aarhus University, Denmark. Gafchromic EBT2 radiochromic films were cut into pieces and irradiated with calibration, conventional and advanced fields. Scanning was done on the parallel beam and Octopus IQ scanner and on a standard document flatbed scanner as reference. An nPAG polymer gel dosimeter was irradiated with a simple four-field box and then scanned with the Octopus scanner and MRI. To test radiochromic plastics, a Presage sample was irradiated and read out using the scanners from the University of Surrey and an identical RapidArc rotational beam field was irradiated on a polymer gel dosimeter and read out using MRI. Results and discussion: The parallel beam EBT2 film evaluation using the flat panel approach gave similar results compared with the flatbed scanner results. The films read out using the Octopus scanner showed potential, but resulted in some differences compared to the flatbed scanner results. The polymer gel readout of the Octopus scanner was almost comparable to the readout from MRI and TPS. The Presage readouts were subordinate to the gel readout with MRI for the same field. To be comparable to the MRI readout, better alignment and newer sample is needed. Conclusions: None of the scanners could be labeled a pure multi-purpose scanner today. However, all scanners show potential and with some further development it is possible that all scanners could be categorized as multi-purpose scanners. This would result in a very useful clinical QA tool.