This article presents an overview of the recent developments and requirements in radiotherapy dosimetry, with particular emphasis on the development of optical fibre dosemeters for radiotherapy applications, focusing particularly on in vivo applications. Optical fibres offer considerable advantages over conventional techniques for radiotherapy dosimetry, owing to their small size, immunity to electromagnetic interferences, and suitability for remote monitoring and multiplexing. The small dimensions of optical fibre-based dosemeters, together with being lightweight and flexible, mean that they are minimally invasive and thus particularly suited to in vivo dosimetry. This means that the sensor can be placed directly inside a patient, for example, for brachytherapy treatments, the optical fibres could be placed in the tumour itself or into nearby critical tissues requiring monitoring, via the same applicators or needles used for the treatment delivery thereby providing real-time dosimetric information. The article outlines the principal sensor design systems along with some of the main strengths and weaknesses associated with the development of these techniques. The successful demonstration of these sensors in a range of different clinical environments is also presented.

No abstract

The aim of this study was to investigate the dosimetric performance of a novel optical fiber sensor for use in external beam radiation therapy. Repeatability and reproducibility of the output signal, linearity, dose rate and dose per pulse dependence were evaluated. Angular dependence was investigated in the axial and azimuthal planes. The percentage depth dose and lateral dose profiles were measured using the optical fiber sensor system and compared to commercially available detectors such as Exradin W1 plastic scintillator and a PTW-microdiamond detector. The result of this study show that the optical fiber sensor system has good repeatability and reproducibility of the output signal with a maximum deviation of 0.17% and 1.00%, respectively. The system also showed an excellent linearity with dose, and its signal was independent of dose rate. However, the system showed a strong dependence on dose per pulse with 27% deviation from the W1 result at the highest dose per pulse value that was achieved at 75 cm source to surface distance. The system also showed an angular dependence when the incident beam was in the azimuthal plane due to the geometry of the scintillator at the tip of the fiber. The optical fiber sensor overresponded when measuring percentage depth dose curves and lateral dose profiles due in part to the sensitivity of the scintillating material (Gd2O2S:Tb) to low energy scattered radiation. However, further investigation is needed to quantify the overall contribution of Cerenkov radiation to the over-response of the optical fiber sensor.

No abstract

Abstract-A characterization study was carried out to determine if a novel, millimetre sized Terbium-activated Gadolinium Oxysulfide optical fibre detector has potential for future use in proton dosimetry. Preliminary studies employed a Theratronics Theratron 780C Cobalt-60 unit and were used to determine nominal dose response, field size response and Čerenkov contributions in 1.25 MeV gamma radiation. Extensive testing was done using 74 MeV protons produced in the TRIUMF 500 MeV cyclotron facility examining raw Bragg peak, spread out Bragg peak, dose response and Čerenkov signal. The detector was low-cost and easily assembled; it showed excellent sensitivity, signal to noise ratio and reproducibility. Quenching at high LET was severe though found to be slightly less than in a commercial scintillating detector. Additional investigations are needed to further explore Čerenkov-only depth-dose curves, signal detection at the extreme distal end of the Bragg peak, and possible sensitivity to neutrons.