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26 November 1996 Optical fibers and radiochromic films for dosimetry in radiotherapy
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A feasibility study of performing radiation dosimetry using a radiochromic film fitted in an optical fiber link is presented. The radio-transducer is the transparent GafchromicTM film, exhibiting a non-reversible blue coloration when exposed to ionizing radiation. Samples of a GafchromicTM sheet have been firstly exposed to different 6 MV X-radiation doses in the 0 - 100 Gy range, and then optically characterized by means of absorption, transmittance and reflectance measurement in the 400 - 900 nm spectral range, in order to choose the best fiber/sensor link assembly. The films showed a usual radiation-modulation absorption spectrum with two main peaks at 614 and 670 nm and null response above approximately 750 nm allowing for two-wavelength differential-attenuation measurements in order to compensate cable and connector losses. As a first approach an optical fiber link has been realized, made of multimode fibers and GRIN-rods, allowing the film insertion in a sleeve between the GRINs. The optical link is connected to an electro-optical unit providing illumination by two LEDs emitting at 655 nm (sensing signal) and 840 nm (reference signal), and detection by a single PIN. The interrogation scheme is based on LED time-domain modulation and subsequent Fourier analysis of the detected signal. Measurements have been performed sequentially inserting the previously radio-exposed films between the GRINs and measuring the ratio between the sensing and reference signals. System output exhibits a dynamics of 14 dB for exposures to doses in the 0 - 100 Gy range, with a dynamics of 2.5 dB and a fairly linear behavior in the 0 - 10 Gy range. The feasibility of using GafchromicTM film for radiation dosimetry in combination with optical fibers has been well documented.
© (1996) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Salvatore Romano, Franco Fusi, E. Bolla, Andrea A. Mencaglia, and Anna Grazia Mignani "Optical fibers and radiochromic films for dosimetry in radiotherapy", Proc. SPIE 2928, Biomedical Systems and Technologies, (26 November 1996);

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