S. O'Keeffe

A review of recent advances in optical fibre sensors for in vivo dosimetry during radiotherapy.

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.

A review of optical fibre radiation dosimeters

Purpose – The purpose of this paper is to provide a detailed review of radiation dosimetry techniques based on optical fibre dosimeters. It presents a comprehensive bibliography of the current research activities in the area.Design/methodology/approach – A range of published work on optical fibre radiation dosimeters are presented, with the merits and limitations discussed. Each radiation dosimetry technique is discussed in turn, providing examples of dosimeters using such techniques reviewed. The main focus is on gamma radiation although other radiation dosimeters are considered.Findings – This paper provides information on the wide range of research activity into radiation dosimeters. The dose ranges of these dosimeters are presented, along with the advantages and disadvantages of different dosimetry techniques.Originality/value – A comprehensive review of published research in the area of solid radiation dosimetry is presented in this paper. It provides an individual with a review of the various techni...

Glucose monitoring using electromagnetic waves and microsensor with interdigitated electrodes

A microscale glucose sensor for biomedical applications was fabricated utilizing the enzyme glucose oxidase and the polymer poly(o-phenylenediamine). A solution containing the enzyme immobilized in the polymer was deposited on interdigitated microelectrodes to form sensor arrays. This was achieved using novel nanopatterning technology offered by BioForce NanoeNabler™. Samples containing different concentrations of glucose were applied to the sensor while the system was being monitored for variances in either current or conductance. The resulting changes in the electrical characteristics of the sensor monitored in real time were found to be proportional to the different concentrations of glucose applied. It is strongly believed that the size reduction of the sensor to a few microns described in this paper creates new opportunities in the areas of chemical and biological sensor development.

Real-time gamma dosimetry using PMMA optical fibres for applications in the sterilization industry

The use of polymethylmethacrylate (PMMA)-based plastic optical fibre as an intrinsic real-time gamma dosimeter is investigated. The radiation-induced attenuation of the fibres is monitored in situ during the course of irradiation. The PMMA fibre exhibited a linear radiation- induced attenuation response at various wavelengths for a dose range of 50 Gy to 50 kGy. The sensitivity, ranging from 0.4 dBm−1 kGy−1 to 0.03 dBm−1 kGy−1, is wavelength dependent, with high sensitivity at the lower wavelengths.

UV LED-based fiber coupled optical sensor for detection of ozone in the ppm and ppb range

A realized novel optical sensor system to measure the concentration of ozone using the emitted light from Light Emitting Diodes in the ultraviolet range is described in this paper. The wavelength selective light interaction of the gas takes place in a fiber coupled and robust reflection cell. The control electronics are separated from the optical sensor head. Therefore it can be used in harsh environment for instance close to discharge plasma in strong electromagnetic fields or at high temperature. The sensor design is potentially low cost, quite small and well suited for a large number of applications. It can be implemented in industrial process control application or in small battery powered hand held devices. This setup is also capable for a parallel and selective measurement of nitrogen dioxide NO2 and sulfur dioxide SO2 - this is already implemented and proved. Further specific LEDs are utilized for this purpose in the setup. For the ozone measurements two different sensor heads where used. A small 4 cm long reflection cell with potential for handheld devices and a 40 cm one thought for high resolution stationary application. The resolution (standard deviation measured at a zero concentration of ozone) of the sensor with the small cell is about 30 ppb at 700 msec measurement time and about 3 ppb at 1,4 sec at the longer cell.

U-bend fibre optic pH sensors using layer-by-layer electrostatic self-assembly technique

A layer-by-layer assembly technique is used to coat layers of nano-thin-films of pH indicator on a U-bend optical fibre to create an effective sensor, using neutral red as the active element. The experimental results characterizing such a pH sensor shows a wide pH sensing range (from pH5 to pH10) fast response.

Plastic optical fibre sensor for spine bending monitoring with power fluctuation compensation

This paper presents the implementation of power fluctuation compensation for an intensity-based optical fibre bending sensor aimed at monitoring human spine bending in a clinical environment. To compensate for the light intensity changes from the sensor light source, a reference signal was provided via the light reflection from an aluminum foil surface fixed at a certain distance from the source fibre end tips. From the results, it was found that the investigated sensor compensation technique was capable of achieving a 2° resolution for a bending angle working range between 0° and 20°. The study also suggested that the output voltage ratio has a 0.55% diversion due to input voltage variation between 2.9 V and 3.4 V and a 0.25% output drift for a 2 h measurement. With the achieved sensor properties, human spine monitoring in a clinical environment can potentially be implemented using this approach with power fluctuation compensation.

Optical fibre radiation dosimetry for low dose applications

An investigation in to the feasibility of using an ultra violet sensitive phosphor coated PMMA optical fibres to aid development of an phosphor coated optical fibre sensor to measure low energy ionising radiation for personal dosimetry applications is presented. The paper provides an overview of the development of a phosphor coated sensor technique and how it can be used to determine variances in light from an Ultra Violet light source. This method can then be used to develop sensors for ionising radiation monitoring. As it is not feasible to use gamma sources for demonstration, the UV detector is used as part of a sensor system prototype for emergency first responders, where ionising radiation monitoring is important in the event of an incident involving radioactive sources.

Optical fibre sensor for the measurement of ozone

The use of optical fibres for the measurement of ozone based on the optical absorption of both UV light at 254nm and visible light at 600nm is investigated and tested. Calculations based on the Beer-Lambert Law are also presented to demonstrate the high resolution of the UV based sensor in determining the concentration of ozone in the range of 0 mg/litre to 1mg/litre and the ability of the visible based sensor to measure high concentrations over a wide range.

Radiotherapy dosimetry based on plastic optical fibre sensors

The use of a PMMA based plastic optical fibre in radiotherapy dosimetry is presented. The optical fibre tip is coated with a scintillation material, terbium-doped gadolinium oxysulfide (Gd2O2S:Tb), which fluoresces under ionising radiation. The emitted signal penetrates the fibre and propagates along the fibre where it is remotely monitored using a fluorescence spectrometer. The results demonstrate good repeatability, with a maximum percentage error of 0.59% and the response is independent of dose rate.