Real-time dosimetry with optical fibre can add to the range of dosimeters available for proton therapy applications. Perfluorinated fibre has demonstrated linearity in radiation-induced attenuation with doses delivered at different energies and it has shown to be highly sensitive and dependent on the wavelength of the probing light source with its highest sensitivity obtained at a wavelength of 460 nm This paper presents the potential of perfluorinated polymer fibre in proton dosimetry applications.
Optical fibres have played an important role in the advancement of real-time dosimetry in clinical applications in recent years. Significant work has been done to increase precision and accuracy in detecting radiation doses during treatment, to avoid the negative effect that can ensue from irradiating healthy tissue around the tumour. The drive to develop distributed measurement in optical fibres has been limited to the slow scanning speed systems from optical time domain reflectometry (OTDR), however for radiotherapy dosimetry, with often short radiation pulse durations, fibre Bragg grating (FBG) interrogation is a better alternative because of the fast-scanning speed. The work presented here includes the preliminary results in the characterisation of CYTOP FBGs on exposure to X-ray radiation emitted from a clinical linear accelerator (linac) machine. A blue shifted linear response of the Bragg wavelength with sensitivity of 6.655 pm/Gy, 6.519 pm/Gy and 7.153 pm/Gy at the three main peaks (1522 nm, 1542 and 1561 nm), was recorded for a 9 Gy of radiation at a dose rate of 1.758 Gy /min with an amplitude fluctuation within the duration of radiation. The response demonstrates the potential for its use in low dose radiation dosimetry, providing for quasi-distributed sensing in radiotherapy.
The complexity of treating cancerous cells in patients using radiotherapy, requires precision in terms of the total dose received by the patient. The use of scintillating materials at the tip of the fibre for real time dosimetry dominate the current development of optical fibre dosimeters, however, they are limited to single point sensing. The changes in the structural and chemical properties in optical fibres on exposure to radiation gives rise to attenuation of the optical signal i.e. Radiation Induced Attenuation (RIA). This has proven to be a useful feature in monitoring radiation from gamma sources (Cobalt60 sources) using PMMA (polymethyl methacrylate) fibres and perfluorinated graded-index polymer optical fibre (Cytop). The aim of this study is to investigate the performance of Cytop fibre in monitoring low doses of X-ray radiation (up to 10 Gy), produced by clinical linear accelerators (linac) for real time monitoring. The radiation induced attenuation (RIA) were measured across a 1 m length of Cytop fibre when the fibre was exposed to different radiation energy (6 MV, 10 MV) from the linac. The result of this study shows that the sensor has a good sensitivity of 0.0693 ± 0.004 dB/m/Gy and 0.0711 ± 0.004 dB/m/Gy at the wavelength of 695 nm and 817 nm respectively, for a radiation energy of 6 MV. Preliminary results demonstrate the potential of the Cytop fibre as a dosimeter for radiation treatment. The Cytop fibre sensor also exhibits a higher sensitivity, in the order of 3, when compared to PMMA optical fibres.
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