Impact of Photon Spectra on the Sensitivity of Polymer Gel Dosimetry by X-Ray Computed Tomography

Introduction: The purpose of the current study was to investigate the effect of X-ray spectra on the sensitivity of a polymer gel dosimeter imaged with a conventional computed tomography (CT) scanner. Material and Methods: The whole process of CT imaging of an irradiated polymer gel was simulated by MCNPX Monte Carlo (MC) code. The imaging of polyacrylamide gel was accomplished by means of a conventional X-ray CT scan machine for different X-ray spectra, including mono-energetic beams and the spectra generated after passing through physical filters, including copper and tin. The MC-scored photon fluence inside simulated detectors was used to reconstruct the axial CT images by MATLAB software. The resultant images were used to derive the dose calibration curve of the gel for different spectra, based on which the highest sensitivity was selected. Results: Among the calculated gel sensitivities for different beam spectra, the highest increase in average sensitivity was obtained as 23% for the 140 kVp spectrum with copper filter and copper+tin filter. However, the sensitivity of mono-energetic beams showed no considerable variation with the increase of energy from 30 to 140 keV. Conclusion: As the findings indicated, the optimization of photon spectra by means of a physical filter could increase the sensitivity of polymer gels in gel dosimetry using CT imaging.