The effect and analysis of terahertz electromagnetic radiation on EBT2 Gafchromic film

Full text: EBT2 Gafchromic film is used in radiotherapy in hospitals for dose readout using visible red light. Terahertz (THz) Time Domain Spectroscopy (TDS) is used to determine if these films are sensitive to frequencies of the range (0.1-2) THz. This will determine in this frequency range: whether films can be read out, if the film has any spectroscopic features, the film's optical properties, and any effect exposure to THz radiation gives. Films were irradiated at intervals of 25 cGy in solid water at 10 cm depth dose by a Varian Linac of 10 x 10 cm2 field size, SSD = 90 cm, with 6 MV photons. Films at each dose where exposed to THz frequency radiation for to min. Films with and without THz radiation exposure where scanned in the flatbed scanner. Results THz TDS displays no measureable differences between irradiated films from 0 to 350 cGy. There are no measureable specific resonances which occur between 0.1 and 2 THz for Gafchromic EBT2 film. THz TDS displayed no difference in film orientation, as expected, since THz frequency radiation has a larger wavelength than visible light. Calibration curves of films exposed to THz agree with those not within experimental error. Variation between films exposed to THz and unexposed randomly varies between -400 and 1100 pixels (Fig. I). Conclusion Radiation doses cannot be read out using THz TDS. No measureable spectroscopic resonances occurred between 0.1 and 2 THz. THz frequency radiation has no measureable effect upon film sensitivity enabling possible dual THz/X-ray systems. (author)