Measurement of dose enhancement close to high atomic number media using optical fibre thermo luminescence dosimeters

Present interest concerns development of a system to measure photoelectron-enhanced dose close to a tissue interface using analogue gold-coated doped silica-fibre thermo luminescence detectors and an X-ray set operating at 250 kVp. Study is made of the dose enhancement factor for various thickness of gold; measurements at a total gold thickness of 160 nm produces a mean dose enhancement factor of 3.19. To verify results, simulations of the experimental setup have been performed. © 2013 Elsevier Ltd. All rights reserved

Measurement of dose enhancement close to high atomic number media using optical fibre thermoluminescence dosimeters

Present interest concerns development of a system to measure photoelectron-enhanced dose close to a tissue interface using analogue gold-coated doped silica-fibre thermoluminescence detectors and an X-ray set operating at 250. kVp. Study is made of the dose enhancement factor for various thicknesses of gold; measurements at a total gold thickness of 160. nm (accounting for incident and exiting photons) produces a mean measured dose enhancement factor of 1.33±0.01 To verify results, simulations of the experimental setup have been performed. © 2013 Elsevier Ltd

Preliminary investigations of two types of silica-based dosimeter for small-field radiotherapy

Two thermoluminescent dosimeters (SiO-GeO doped fibres and glass beads (GB)) were used to measure small photon field doses and compared against GAFCHROMIC film, a small ionisation chamber (RK-018) and a p-type silicon diode (SCANDITRONIX, F1356), as well as Monte Carlo simulations with FLUKA and BEAMnrc/DOSXYZnrc. Ge-doped SiO fibres have been shown by this group to offer a viable system for use as dosimeters. The fibres and GB offer good spatial resolution (~120μm and 2mm respectively), large dynamic dose range (with linearity from tens of mGy up to well in excess of many tens of Gy), are non-hygroscopic and are of low cost. Measurements of beam profiles for field sizes of 10mm×10mm, 20mm×20mm, 30mm×30mm, 40mm×40mm, and 100mm×100mm were carried out. Through the use of a customised solid water phantom, doped optical fibres and GBs were placed at defined positions along the x-and y-axes to allow accurate beam profile measurement. The maximum difference between FWHM measurements was 1.8mm. For penumbra measurements (measured between 80% and 20% isodoses), the maximum difference was<1mm. These measurements indicate good agreement, within measurement uncertainty, with Gafchromic film, data obtained from the use of two commonly used detectors and FLUKA and BEAMnrc/ DOSXYZnrc simulations. © 2014 Elsevier Ltd

Development of tailor-made silica fibres for TL dosimetry

The Ge dopant in commercially available silica optical fibres gives rise to appreciable thermoluminscence (TL), weight-for-weight offering sensitivity to MV X-rays several times that of the LiF dosimeter TLD100. The response of these fibres to UV radiation, X-rays, electrons, protons, neutrons and alpha particles, with doses from a fraction of 1Gy up to 10kGy, have stimulated further investigation of the magnitude of the TL signal for intrinsic and doped SiO fibres. We represent a consortium effort between Malaysian partners and the University of Surrey, aimed at production of silica fibres with specific TL dosimetry applications, utilizing modified chemical vapour deposition (MCVD) doped silica-glass production and fibre-pulling facilities. The work is informed by defect and dopant concentration and various production dependences including pulling parameters such as temperature, speed and tension; the fibres also provide for spatial resolutions down to <10μm, confronting many limitations faced in use of conventional (TL) dosimetry. Early results are shown for high spatial resolution (~0.1mm) single-core Ge-doped TL sensors, suited to radiotherapy applications. Preliminary results are also shown for undoped flat optical fibres of mm dimensions and Ge-B doped flat optical fibres of sub-mm dimensions, with potential for measurement of doses in medical diagnostic applications. © 2014 Elsevier Ltd

Development of tailor-made silica fibres for TL dosimetry

The Ge dopant in commercially available silica optical fibres gives rise to appreciable thermoluminscence (TL), weight-for-weight offering sensitivity to MV x-rays several times that of the LiF dosimeter TLD100. The response of these fibres to UV radiation, X-rays, electrons, protons, neutrons and alpha particles, with doses from a fraction of 1 Gy up to 10 kGy, have stimulated further investigation of the magnitude of the TL signal for intrinsic and doped SiO2 fibres. We represent a consortium effort between Malaysian partners and the University of Surrey, aimed at production of silica fibres with specific TL dosimetry applications, utilising modified chemical vapour deposition (MCVD) doped silica-glass production and fibre-pulling facilities. The work is informed by defect and dopant concentration and various production dependencies including pulling parameters such as temperature, speed and tension, the fibres also providing for spatial resolutions down to<10 µm, confronting the many limitations faced in use of conventional (TL) dosimetry. Early results are shown for high spatial resolution (∼ 0.1 mm) single-core Ge-doped TL sensors, suited to radiotherapy applications. Preliminary results are also shown for undoped flat optical fibres of mm dimensions and Ge-B doped flat optical fibres of sub-mm dimensions, with potential for measurement of doses in medical diagnostic applications