Peter Woulfe

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.

Radiation Dosimeter Using an Extrinsic Fiber Optic Sensor

A novel extrinsic optical fiber X-ray dosimeter for biomedical applications is presented in this paper. The primary focus of the sensor is to measure low doses of ionizing X-ray radiation. The material in the sensor tip scintillates upon exposure to radiation and the resultant low level scintillating light is coupled to a polymethylmethacrylate plastic optical fiber, which guides it toward a distant fluorescent optical spectrometer. The optical spectrometer measures the low level scintillating light from the sensor and converts the ionizing radiation energy to measurable arbitrary optical intensity units. Initial testing showed the scintillating optical fiber X-ray dosimeter exhibits an acceptable sensitivity upon excitation from a calibrated X-ray source. Further examinations of the sensor revealed good response and repeatability of measurement for various levels of low energy ionizing X-ray energy. The sensor was found to exhibit a maximum of 3.23% variance from the average value over ten repetitions. The sensor is sensitive from 50 kVp X-ray energy which continued exponentially up to 140 kVp where the response began to taper off. The sensor demonstrated excellent spectral response upon exposure to 6 MV and 15 MV ionizing X-ray radiation energy from a Siemens Avant Garde linear accelerator. It showed excellent repeatability of measurement upon repeated actuation of the radiation over short bursts of time. The sensor demonstrates very good stability of response during on radiation periods, showing a maximum of 2% variation of the full scale value in each case. This type of optical fiber X-ray dosimeter was tested in the University of Limerick (Ireland), the National Institute for Lasers, Plasma and Radiation Physics (Romania), and the Galway Clinic in Ireland. Further investigations were performed by all three facilities to better characterize additional features of the sensor for different X-ray radiation energies.

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.

Plastic optical fibre sensor for in-vivo radiation monitoring during brachytherapy

An optical fibre sensor is presented for applications in real-time in-vivo monitoring of the radiation dose a cancer patient receives during seed implantation in Brachytherapy. The sensor is based on radioluminescence whereby radiation sensitive scintillation material is embedded in the core of a 1mm plastic optical fibre. Three scintillation materials are investigated: thallium-doped caesium iodide (CsI:Tl), terbium-doped gadolinium oxysulphide (Gd2O2S:Tb) and europium-doped lanthanum oxysulphide (La2O2S:Eu). Terbium-doped gadolinium oxysulphide was identified as being the most suitable scintillator and further testing demonstrates its measureable response to different activities of Iodine-125, the radio-active source commonly used in Brachytherapy for treating prostate cancer.

Terbium-doped gadolinium oxysulfide (Gd2O2S:Tb) scintillation-based polymer optical fibre sensor for real time monitoring of radiation dose in oncology

A PMMA based plastic optical fibre sensor for use in real time radiotherapy dosimetry is presented. The optical fibre tip is coated with a scintillation material, terbium-doped gadolinium oxysulfide (Gd2O2S:Tb), which fluoresces when exposed to ionising radiation (X-Ray). The emitted visible light signal penetrates the sensor optical fibre and propagates along the transmitting fibre at the end of which it is remotely monitored using a fluorescence spectrometer. The results demonstrate good repeatability, with a maximum percentage error of 0.5% and the response is independent of dose rate.

Scintillating optical fibre sensor for radiotherapy dosimetry

An optical fibre sensor for monitoring low dose radiation is presented. The sensor is based on a scintillation material coated optical fibre, which emits visible light when exposed to low level ionising radiation. The incident level of ionising radiation can be determined by analysing the observed emission spectra. The work presented reports on the design of the sensor and the stability of the sensor during measurement of incident x-ray energy. Initial testing of the sensor at the radiotherapy facility at the Galway Private Clinic is presented, demonstrating the suitability of such a sensor for a range of radiotherapy dosimetry applications.

Optical fibre sensors: their role in in vivo dosimetry for prostate cancer radiotherapy

Review is made of dosimetric studies of current optical fibre technology in radiotherapy for therapeutic applications, focusing particularly on in vivo dosimetry for prostate radiotherapy. We present the various sensor designs along with the main advantages and disadvantages associated with this technology. Optical fibres are ideally placed for applications in radiotherapy dosimetry; due to their small size they are lightweight and immune to electromagnetic interferences. The small dimensions of optical fibres allows it to be easily guided within existing brachytherapy equipment; for example, within the seed implantation needle for direct tumour dose analysis, in the urinary catheter to monitor urethral dose, or within the biopsy needle holder of the transrectal ultrasound probe to monitor rectal wall dose. The article presents the range of optical fibre dosimeter designs along with the main dosimetric properties required for a modern in vivo dosimetry system to be utilised in a clinical environment.

Radioluminescence based optical fibre sensor for radiation monitoring during brachytherapy

An optical fibre sensor is presented, based on radioluminescence whereby radiation sensitive scintillation material, terbium doped gadolinium oxysulphide (Gd2O2S:Tb), is embedded in the core of a plastic optical fibre. The sensor is designed for in-vivo monitoring of the radiation dose during radio-active seed implantation for brachytherapy, in prostate cancer treatment, providing oncologists with real-time information of the radiation dose to the target area and/or nearby critical structures. The radiation from the brachytherapy seeds causes emission of visible light from the scintillation material through the process of radioluminescence, which penetrates the fibre, propagating along the optical fibre for remote detection using a multi-pixel photon counter. The sensor demonstrates a high sensitivity to Iodine-125, the radioactive source most commonly used in brachytherapy for treating prostate cancer. Further results show a discernible increase in photon counts for increasing activities of Iodine-125.

Characterisation of radioluminesence based optical fibre dosimeter in radiotherapy beam applications

A PMMA (polymethyl methacrylate) based plastic optical fibre is coated with radiation sensitive inorganic scintillators that fluoresce when exposed to ionising radiation. The emitted signal penetrates the fibre and propagates along the fibre where it is remotely monitored using a fluorescence spectrometer. The dosimeter is characterised for a range of parameters associated with radiotherapy treatment plans, including field size and dose rate. The results demonstrate good repeatability, with a maximum percentage error of 0.59% and the response is independent of dose rate.

Optical Fibre Based Scintillation Probe for Radiotherapy Dosimetry

A PMMA based plastic optical fibre coated with radiation sensitive inorganic scintillators, which fluoresce when exposed to ionising radiation, is presented for use in applications for monitoring radiation doses a patient receives during radiotherapy.