Characterization of Ge-doped optical fibres for MV radiotherapy dosimetry

Ge-doped optical fibres offer promising thermoluminescence (TL) properties together with small physical size and modest cost. Their use as dosimeters for postal radiotherapy dose audits of megavoltage photon beams has been investigated. Key dosimetric characteristics including reproducibility, linearity, dose rate, temperature and angular dependence have been established. A methodology of measuring absorbed dose under reference conditions was developed. The Ge-doped optical fibres offer linearity between TL yield and dose, with a reproducibility of better than 5%, following repeated measurements (n=5) for doses from 5 cGy to 1000 cGy. The fibres also offer dose rate, angular and temperature independence, while an energy-dependent response of 7% was found over the energy range 6 MV to 15 MV (TPR20,10 of 0.660, 0.723 and 0.774 for 6, 10 and 15 MV respectively). The audit methodology has been developed with an expanded uncertainty of 4.22% at 95% confidence interval for the photon beams studied

The effect of TiO2 and MgO on the thermoluminescence properties of a lithium potassium borate glass system

The influence of dopant TiO2 and co-dopant MgO on the thermoluminescence (TL) properties of lithium potassium borate glass (LKB) is reported in this paper. The glow curve exhibits a prominent peak (Tm) at 230 °C. The TL intensity was enhanced by a factor of ~3 due to the incorporation of MgO, and this was attributed to the creation of extra electron traps mediated by radiative recombination energy transfer. We achieved good linearity of the TL yield with dose, low fading, excellent reproducibility and a promising effective atomic number (Zeff=8.89), all of which are highly suitable for dosimetry. The effect of heating rate, sunlight and dose rate on the TL are also examined. These attractive features demonstrate that our dosimeter is useful in medical radiation therapy

Effect of temperature on the epr response of gamma irradiated potassium tartrate hemihydrate

Electron paramagnetic resonance (EPR) can be used as radiation detection for appropriate materials exposed to ionizing radiation. In this study, potassium tartrate hemihydrate (PT) was irradiated with Co-60 gamma rays with absorbed dose range from 1 to 9 Gy. The effect of temperature to the unirradiated and irradiated samples were investigated using electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra were recorded in the temperature range from room temperature (293 K) to 413 K. The results show that the unirradiated PT sample does not exhibit any EPR signal when thermal energy is given to the sample. However, the irradiated PT samples exhibit EPR spectrum with three lines recorded at room and high temperatures. The main strong line dominates the spectrum of the irradiated PT sample appears at g = 2.0032. Heating the irradiated sample above room temperature showed increases in signal intensity. The dose response curves of the signal at variable temperature were described well by a linear function

Polymethacrylic Gel (Pmag) as a Point Dosimeter.

Polymethacrylic gel (PMAG) of different concentrations of MAA and BIS were irradiated using γ-rays produced by 60Co radionuclide with the absorbed doses ranging from 0 Gy to 19 Gy. Due to the radiation-induced polymerization processes, the formation of Polymethacrylic gel (PMAG) occurs, which causes the dose response mechanism increased in the Nuclear Magnetic Resonance (NMR) relaxation rates of protons. The relaxation rate R2 (1/T2) are fitted to the functional form y as a function of absorbed dose D was found to have a monoexponential expression in the form; y= y + A (1-e -D/D). The relaxation rate (ΔR2) dose sensitivity value (12.5 + 0.1 Gy) of MAA monomer by Lepage, et al 2001 is comparable with PMAAG experimental value gained which are 12.6 + 0.1 Gy. The dose sensitivity, D0 and half dose, D1/2 was found increasing with the concentrations of MAA monomer and BIS crosslinker. The slope parameter kBIS > kMAA indicates that consumption of crosslinker is much faster than monomer. Eventually, UV-Vis spectrophotometer was used to record PMAG degree of absorption. The PMAG has a mean value of absorption of 0.614 at 375 nm. The dose derived from PMAG is comparable to Fricke dosimeter and ionization chamber readings between 4.7 ± 0.1% and 11.6 ± 0.1%. The dose errors of less than 10 ± 0.1% are considered acceptable in radiation processing, an improvement of accuracy less than 5.0 ± 0.1% is acceptable in radiotherapy. This effort is to undertake the study of precision and accuracy associated with the use of Fricke and polymer gel in optimizing the usage of gels for dosimetry

EPR dosimeter material properties of potassium tartrate hemihydrate

The ability of potassium tartrate hemihydrate as a radiation sensitive material for electron paramagnetic resonance (EPR) dosimetry was investigated. The samples were subjected to different doses, in the range of 1-9 Gy of 60Co gamma rays at room temperature. The EPR spectra were investigated through variation of signal intensity with respect to absorbed dose, magnetic field modulation amplitude, microwave power and time stability. The results indicate that the sensitivity of potassium tartrate hemihydrate is about 30% higher than that of alanine. However, the EPR signal is timely less stable within the first two weeks after irradiation

Thermoluminescence properties of CaO-B2O3 glass system doped with GeO2

The aim of this study is to investigate the thermoluminescence properties of germanium doped calcium borate glass for thermoluminescence dosimeter used. Glasses with composition (30-x) CaO-70B2O3: xGeO2 where x=0.1, 0.2, 0.3, 0.4 and 0.5mol% were prepared using a melt-quenching method. The glasses were irradiated to 60Co gamma ray with doses ranging from 0.5Gy to 4.0Gy. The amorphous phases were identified for all glass samples. The glow curves were analyzed to determine various characterizations of a thermoluminescence dosimeter of the glass. It was found that the sample with a concentration of 0.1mol% GeO2 has the best thermoluminescence characteristics such as linearity, sensitivity, fading characteristic, minimum detectable dose and effective atomic number. The results clearly showed that germanium doped calcium borate glass has a potential to be considered as the thermoluminescence dosimeter

Dosimetric characteristics of fabricated silica fibre for postal radiotherapy dose audits

Present investigation aims to establish the dosimetric characteristics of a novel fabricated flat fibre TLD system for postal radiotherapy dose audits. Various thermoluminescence (TL) properties have been investigated for five sizes of 6 mol% Ge-doped optical fibres. Key dosimetric characteristics including reproducibility, linearity, fading and energy dependence have been established. Irradiations were carried out using a linear accelerator (linac) and a Cobalt-60 machine. For doses from 0.5 Gy up to 10 Gy, Ge-doped flat fibres exhibit linearity between TL yield and dose, reproducible to better than 8% standard deviation (SD) following repeat measurements (n = 3). For photons generated at potentials from 1.25 MeV to 10 MV an energy-dependent response is noted, with a coefficient of variation (CV) of less than 40% over the range of energies investigated. For 6.0 mm length flat fibres 100 μm thick × 350 pm wide, the TL fading loss following 30 days of storage at room temperature was < 8%. The Ge-doped flat fibre system represents a viable basis for use in postal radiotherapy dose audits, corrections being made for the various factors influencing the TL yiel