Glass beads and Ge-doped optical fibres as thermoluminescence dosimeters for small field photon dosimetry.

An investigation has been made of glass beads and optical fibres as novel dosimeters for small-field photon radiation therapy dosimetry. Commercially available glass beads of largest dimension 1.5 mm and GeO2-doped SiO2 optical fibres of 5 mm length and 120 µm diameter were characterized as thermoluminescence dosimeters. Results were compared against Monte-Carlo simulations with BEAMnrc/DOSXYZnrc, EBT3 Gafchromic film, and a high-resolution 2D-array of liquid-filled ionization chambers. Measurements included relative output factors and dose profiles for square-field sizes of 1, 2, 3, 4, and 10 cm. A customized Solid-Water® phantom was employed, and the beads and fibres were placed at defined positions along the longitudinal axis to allow accurate beam profile measurement. Output factors and the beam profile parameters were compared against those calculated by BEAMnrc/DOSXYZnrc. The output factors and field width measurements were found to be in agreement with reference measurements to within better than 3.5% for all field sizes down to 2 cm2 for both dosimetric systems, with the beads showing a discrepancy of no more than 2.8% for all field sizes. The results confirm the potential of the beads and fibres as thermoluminescent dosimeters for use in small photon radiation field sizes.

Radiation protection in fixed PET/CT facilities--design and operation.

We describe the design of a fixed positron emission tomography (PET)/CT facility and the use of a simulated instantaneous dose-rate plot to visually highlight areas of potentially high radiation exposure. We also illustrate the practical implementation of basic radiation protection principles based on the use of distance and shielding and the minimisation of time spent in hot areas. Staff whole body doses for 4 years are presented with results of an optimisation study analysing the dose arising from the different phases within each study using direct reading dosemeters. The total whole body dose for all staff for each patient fell from 9.5 µSv in the first full year of operation to 4.8 µSv in 2008. The maximum dose to an individual member of staff per patient decreased over the same period from 3.2 to 0.9 µSv. The optimisation study showed that the highest dose was recorded during the injection phase.

Standardisation of positron-emitters in gas with the NPL primary gas counting system.

A primary standard for positron-emitters in gas has been developed. The method involves internal gas proportional counting and the use of the PENELOPE Monte Carlo code to determine corrections for counting losses. The development work was carried out using (11)C, although the method can be applied to other positron emitters. The results were compared with measurements of (11)C (in solution) carried out using a secondary standard re-entrant ionisation chamber previously calibrated with reference to absolute counting techniques.

A detailed Monte Carlo accounting of radiation transport in the brain during BNCT.

The collision type central to BNCT is (10)B(n, alpha)(7)Li, however, other types of nuclear reactions also take place in the patient. In addition to the major elements (H, C, N, O), minor elements such as Na, Mg, P, S, Cl, K, Ca and Fe present in body tissues also interact in neutron collisions. Detailed accounting of the above not only provides a better understanding of radiation transport in the human body during BNCT, but such knowledge affects the design of the facility, as well as treatment planning, imaging and verification for a given BNCT agent. Of the methods of investigation currently available, only Monte Carlo simulation could provide the detailed accounting and breakdown of the quantities required. We report Monte Carlo simulation of an anthropomorphic voxel phantom, the VIP-Man and show how these quantities change with different (10)B concentrations in the tumour, the blood and the remaining tissues. The (10)B biodistribution has been chosen to be the variable of interest, since it is not accurately known, is frequently approximated and is a crucial quantity upon which dose calculations are based.

Non-convergence of Geant4 hadronic models for 10 and 30 MeV protons in 18O and 14N.

We investigated Geant4 Monte Carlo simulation of protons interactions in (18)O and (14)N. With proton incident energies of 10 and 30 MeV, we compared the different Geant4 models available for proton inelastic collisions: the low-energy parameterisation, Bertini cascade and precompound models. The models produced different (1) combinations of secondary particles and (2) final states of secondary particles. The non-convergence suggests that the hadronic models, yet to be benchmarked for this energy range, are not ready for production-mode problem-solving.

Epigastric electrical impedance for the quantitative determination of the gastric acidity.

Electrical impedance measurements have been used by scientists since the 1980s to investigate the gastric function. In this work, these measurements were carried out using the epigastrograph, a device generating alternating current of 32 kHz and injecting it in the gastric area of the human body with surface electrodes, located around the abdominal area. Although the method has been used for about three decades the physiological interpretation of these measurements is still under research. This work states that the electrical impedance measurements from the gastric area depend on the conductivity of the gastric lumen, due mainly to gastric acid secretions and to the conductivity and chemical form of the ingested meal. By choosing the proper test meal the gastric acidity in the empty, healthy stomach was also estimated. The estimated value is in accordance with the literature. The method is non-invasive, relatively inexpensive, simple to medical technologists and subjects, and involves no radiation risk. The method may form the basis for the development of a non-invasive gastric pH meter.

Lithium-gadolinium-borate as a neutron dosemeter.

Lithium-gadolinium-borate (LGB) dispersed as microcrystals within the plastic scintillator BC-490 is a promising material for accurate neutron dosimetry in mixed n/gamma fields. Spectral information > 1 MeV is obtained by capture gating proton recoil events in the plastic scintillator to subsequent capture in (6)Li. Below 1 MeV, isolated capture events in either gadolinium or (6)Li give energy information in this region. Discrimination based on capture gating is used to reject false coincidences due to gamma rays or incorrectly gated neutron events. A detailed Monte Carlo model has been created in MCNPX that predicts the energy response of the LGB spectrometer in the capture-gated mode of operation. X-ray microtomography has been performed on the detector in order to obtain the LGB microcrystal distribution within the plastic scintillator, and this is incorporated into the model. The way in which the calculated response functions can be included in an unfolding procedure is outlined.

A high-resolution anthropomorphic voxel-based tomographic phantom for proton therapy of the eye.

Proton therapy is increasingly used in medical treatments for cancer patients due to the sharp dose conformity offered by the characteristic Bragg peak. Proton beam interactions with the eye will be simulated using the MCNPX Monte Carlo code and available nuclear cross-section data to calculate the dose distribution in the eye gel and surrounding organs. A high-resolution eye model will be employed using a 3D geometrical voxel-based anthropomorphic head phantom obtained from the Visible Human Project (female data). Manual segmentation of the eye, carried out by the Medical Physics group at the University of Surrey resulted in 15 identified structures. This work emphasizes the use of a realistic phantom for accurately predicting dose deposition by protons.

Radioactivity levels of staple foodstuffs and dose estimates for most of the Tanzanian population.

Levels of natural radioactivity in staple food products (maize and rice) from various localities of Tanzania have been studied. The average activity concentrations of 40K, 232Th and 238U in maize were 48.79 +/- 0.11, 4.08 +/- 0.01 and 13.23 +/- 0.10 Bq kg(-1), respectively. In rice the concentrations of 40K, 232Th and 238U were 24.67 +/- 0.03, 3.82 +/- 0.02 and 5.02 +/- 0.02 Bq kg(-1), respectively. 137Cs was detected in only one sample collected in Zanzibar. The sample, with activity concentration of 5.57 +/- 0.01 Bq kg(-1), had been imported from Thailand. The relatively high average concentrations of the radionuclides in maize compared to rice may be attributed to the extensive use of phosphate fertilizers in maize production in Tanzania. Total annual committed effective doses due to total 232Th and 238U intakes as a result of consumption of staple foodstuffs for infants, children and adults were 0.16, 0.29 and 0.36 mSv y(-1), respectively, which are lower than the annual dose guideline for the general public.

Neutron-fluence-to-dose conversion coefficients in an anthropomorphic phantom.

A set of fluence-to-effective-dose conversion coefficients has been calculated for neutrons with energies <20 MeV using a high-resolution anthropomorphic phantom (Zubal model) and the MCNPX code. The calculation used 13 monodirectional monoenergetic neutron beams in the energy range 10(-9) to 20 MeV, under three different source irradiation configurations: anterior-posterior, posterior-anterior and left lateral. Dose calculations were performed for 18 selected organs of the body, for which the International Commission on Radiological Protection and the International Commission on Radiological Units and Measurements have set tissue weighting factors for the determination of the effective dose. Another set of neutron-fluence-to-effective-dose conversion coefficients was also calculated with the proposed modification wR from ICRP Publication 92. From comparison between the dose results calculated and the data reported for the MIRD and VIPMAN models, it can be concluded that, although some discrepancies exist between the Zubal model and the two other models, there is good agreement in the left lateral irradiation geometry.

Development and testing of an active area neutron dosemeter.

This paper describes the design, development and testing of an active area neutron dosemeter (AAND). The classic moderator and central detector is retained but in AAND this arrangement is augmented by small thermal neutron detectors positioned within the moderating body. The outputs from these detectors are combined using an appropriately weighted linear superposition to fit both the ambient dose equivalent and the radiation weighting factor. Experimental verifications of both the modelled detector energy reponses and the overall AAND response are given. In the relatively soft D2O moderated 252Cf spectra, the AAND determined both the H*(10) and mean radiation weighting factor to better than +10%.

Introduction of a thermal response to the DSTL PADC personal neutron dosemeter.

The response of the Defence Science and Technology Laboratory (DSTL) PADC personal neutron dosemeter is strongly dependent upon neutron energy, with a range of 300-500 tracks per cm2 per mSv for energies between 1 and 5 MeV. Below 1 MeV the response drops off sharply. This lack of sensitivity is undesirable when the dosemeter is employed with the softened fission spectra encountered in the workplace. In order to incorporate a thermal response, a polypropylene converter doped with LiF has been placed directly in front of the PADC elements. Tritons produced in the thermal neutron reaction 6Li (n,t)alpha at 2.7 MeV will then penetrate the PADC, leaving a trail of damage. The reaction rate within the converter has been calculated using MCNP for thermal neutrons and a range of higher energies, while transport of the tritons is modelled using the SRIM/TRIM package to determine the resultant track density and depth distribution. The modelling and experimental work have demonstrated that a concentration of 0.2% natural lithium by weight results in a track density in a thermal field comparable with that produced per unit personal dose equivalent by neutrons greater than 1 MeV in the standard dosemeter. Additional MCNP modelling has demonstrated that the dosemeters' albedo response to intermediate energy neutrons can be enhanced considerably by placing a boron-doped shield in front of the converter and increasing its lithium concentration.

Response of a lithium gadolinium borate scintillator in monoenergetic neutron fields.

Accurate estimation of neutron dose requires knowledge of the neutron energy distribution in the working environment. Existing neutron spectrometry systems, Bonner spheres for example, are large and bulky, and require long data acquisition times. A portable system that could indicate the approximate neutron energy spectrum in a short time would be extremely useful in radiation protection. A composite scintillator, consisting of lithium gadolinium borate crystals in a plastic scintillator matrix, produced by Photogenics is being tested for this purpose. A prototype device based on this scintillator and digital pulse processing electronics has been calibrated using quasi-monoenergetic neutron fields at the low-scatter facility of the UK National Physical Laboratory (NPL). Energies selected were 144, 250, 565, 1400, 2500 and 5000 keV, with correction for scattered neutrons being made using the shadow cone technique. Measurements were also made in the NPL thermal neutron field. Pulse distributions collected with the digitiser in capture-gated mode are presented, and detection efficiency and energy resolution derived. For comparison, neutron spectra were also collected using the commercially available Microspec N-Probe from Bubble Technology Industries, which consists of an NE213 scintillator and a 3He proportional counter.

Whole body [O-15]water pharmacokinetics measured in blood.

A simple pharmacokinetic model to explain the time course of [O-15] water in human whole blood after bolus injection is described. The model has been derived from measurements in twelve healthy volunteers who were measured repeatedly, resulting in 67 datasets, made in the context of PET blood flow studies. In contrast to traditional volume of distribution estimates of total body water (TBW) which rely on measurements after many hours, the model and data provide insights into the fast uptake components in the distribution of water in the body. Data fitting shows that the volume of distribution of fast exchanging tissues is 21 l. TBW was calculated to be 37 l. Monte Carlo simulation showed that the expected inaccuracy of determination of parameters due to unsystematic sources in the measurement data was around 5% for most parameters. Our data show that water extraction to tissue is somewhat higher than would be predicted from the tabulated values, probably because skeletal blood flow is sensitive to physiological status and environmental conditions. The study provides valuable reference data on the distribution and kinetics of water in man. Using the parameters and model from this study, reference input time-activity curves can be calculated, e.g. for the Monte Carlo study of error propagation in PET studies.

Physiological interpretation of electrical impedance epigastrography measurements.

Measurement of the electrical impedance of the gastric region is carried out with the epigastrograph. This generates and applies alternating current around the abdominal area and measures the potential difference in order to determine the impedance externally, via electrodes. The change of epigastric impedance for a subject, given a meal after fasting, depends on the conductivity of the meal compared to the stomach and surrounding tissues. Typically a conductive meal has conductivity >7 mS cm(-1), non-conductive <2 mS cm(-1) and neutral about 4.5 mS cm(-1). Half-emptying times (T50s) from gastric emptying studies in volunteers using three test meals of 450 ml volume were obtained and found to be shorter than expected from the literature. The meals were a 10% glucose solution and two milk shakes of energy 1,300 kJ and 2,850 kJ, respectively. These electrical impedance epigastrography (EIE) measurements were carried out with scintigraphy. The T50 values of the latter were significantly longer. The direct comparison of the normalized experimental data obtained by both methods led to the concept that EIE measurements are mainly influenced by gastric secretion. Thus the EIE trace of a 'neutral' meal suggests the hypothesis that the volume of the meal is not the significant factor but is influenced by gastric acid secretions. Physiology of the gastric mucosa during the digestion of a meal and intragastric pH values also suggests this. Gastric function studies using EIE measurements may therefore reflect gastric ionic concentration rather than the volume of the contents of the stomach. In turn this could lead to the development of a non-invasive method for the continuous recording of gastric acid secretions.

Determination of cadmium and zinc in Alzheimer's brain tissue using inductively coupled plasma mass spectrometry.

In this work, brain tissue was taken from Alzheimer's Disease (AD) subjects (n=11), 'normal' subjects (n=10) and from subjects with senile involutive cortical changes (SICC) (n=6). Concentrations of Cd and Zn were determined in all samples, using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The brain tissue was selected and obtained from the Netherlands Brain Bank. Samples were taken in each case, from both hemispheres of the superior frontal gyrus, the superior parietal gyrus, the medial temporal gyrus, the hippocampus and the thalamus of the same brain.Cd which is known to have no essential role in the brain was found to follow, as expected, a lognormal distribution of concentrations in 'normal' subjects (Shapiro-Wilk's test (0.98) (p<0.18)). For the Alzheimer's Disease subjects and SICC subjects, the data tends to follow a lognormal distribution, rather than a normal distribution, but is still significantly different from it (Shapiro-Wilk's test (0.97) (p<0.03); (0.93) (p<0.0067), respectively)). In the case of Zn concentrations, the data tends to follow a normal distribution for the 'normal' subject group, even though the data is significantly different from it (Shapiro-Wilk's test (0.95) (p<0.001)). Whereas in the Alzheimer's Disease and SICC subject groups, the data follows a normal distribution (Shapiro-Wilk's test (0.98) (p<0.21); (0.97) (p<0.2002), respectively)). When comparing age-matched groups, for all regions and both hemispheres, no significant differences (p>0.1) for Cd were found between 'normals' and Alzheimer's Disease subjects and Alzheimer's Disease subjects and SICC but at a low level of significance, lower concentrations of Cd were found in the SICC group compared to the 'normals'. For all regions and both hemispheres, Zn was found to be significantly decreased in the Alzheimer's Disease group, compared to the 'normal' and SICC groups. Zn concentrations were also found to be significantly decreased in the 'normals' compared to the SICC group. It is also of interest that Cd negatively correlates with the scale of tangles in both 'normals' (p<0.001) and Alzheimer's Disease subjects (p<0.01). In the SICC subjects Cd correlates negatively with the tangles but not significantly so (p>0.1).

Diagnostic features of Alzheimer's disease extracted from PET sinograms.

Texture analysis of positron emission tomography (PET) images of the brain is a very difficult task, due to the poor signal to noise ratio. As a consequence, very few techniques can be implemented successfully. We use a new global analysis technique known as the Trace transform triple features. This technique can be applied directly to the raw sinograms to distinguish patients with Alzheimer's disease (AD) from normal volunteers. FDG-PET images of 18 AD and 10 normal controls obtained from the same CTI ECAT-953 scanner were used in this study. The Trace transform triple feature technique was used to extract features that were invariant to scaling, translation and rotation, referred to as invariant features, as well as features that were sensitive to rotation but invariant to scaling and translation, referred to as sensitive features in this study. The features were used to classify the groups using discriminant function analysis. Cross-validation tests using stepwise discriminant function analysis showed that combining both sensitive and invariant features produced the best results, when compared with the clinical diagnosis. Selecting the five best features produces an overall accuracy of 93% with sensitivity of 94% and specificity of 90%. This is comparable with the classification accuracy achieved by Kippenhan et al (1992), using regional metabolic activity.

Molecular and phylogenetic analysis of haemagglutinin and neuraminidase sequences from recent human influenza type A (H3N2) viral isolates in Southern Greece.

Eighteen haemagglutinin (HA1) gene segments and eleven neuraminidase (NA) genes of human influenza type A (H3N2) viruses isolated from non-vaccinated individuals presenting severe influenza-like illness at peak influenza activity in Southern Greece during the surveillance period 1996-1999, were subjected to sequence and phylogenetic analyses following propagation in embryonated hen's eggs. The HA1 gene segment of the clinical isolates differed from the recent reference influenza type A (H3N2) vaccine strains in an Ile at residue 186, a Val at residue 194 and a Val at residue 226 for one, two and thirteen isolates of the 1996-1997 and 1996-1999 periods, respectively. The analogous differences in the NA gene were confined in an Asp to Asn substitution at residue 198 in one A/Wuhan/359/95 (H3N2)-like isolate of the 1996-1997 period, primarily. In addition, phylogenetic analysis revealed that an isolate of the 1997-1998 period was a recombinant with its HA1 gene segment being closely related to that of A/Wuhan/359/95-like viruses and its NA to viruses of the A/Sydney/5/97 (H3N2) lineage. These findings confirmed the profound genetic instability of influenza type A (H3N2) viruses and underscored the importance for periodic molecular surveys of HA and NA in the effective prevention and management of viral outbreaks. Most importantly, however, they contributed the first complete epidemiological material for influenza in Southern Greece, the archival nature of which constitutes valuable reference for future surveys.

Molecular detection and identification of an enterovirus during an outbreak of aseptic meningitis.

Stool samples from sixteen cases of children with meningitis originating from four different and geographically isolated parts of Greece were investigated for enteroviruses. The conventional method of cell culture in four different cell lines was initially used for the isolation of enteroviruses. The results showed a cytopathic effect (CPE) in all cases after two, or even more successive passages in only one cell line (RD), although a less-than-satisfactory CPE was obtained in many cases. Seroneutralization with RIVM mixed hyperimmune antisera followed and the isolates were typed as Coxsackie B viruses. The method of RT-PCR with enterovirus-specific primers targeted to the highly conserved 5'-UTR of the genome was initially used for the detection of enteroviruses from the inoculated cell cultures. A positive RT-PCR result was obtained for all of the clinical samples rapidly and accurately and the isolates were further characterized with the aid of Restriction Fragment Length Polymorphism (RFLP) analysis and Single Strand Conformation Polymorphism analysis (SSCP) of the amplicons. The RFLP analysis showed first of all that the isolates had an identical restriction pattern with Coxsackie B5 Faulkner reference strain with 4 out of 5 restriction enzymes and secondly, both RFLP and SSCP analysis indicated the epidemiological association of the isolates. The speed of the molecular methodology that was used in comparison with the conventional methods and its possible significance for the description of virus evolution and circulation in the populations is discussed.