Dosimetry of indigenously developed 177Lu patch source for surface brachytherapy-Experimental and Monte Carlo methods.

This paper describes the evaluation of dosimetry characteristics of an in-house developed 177Lu skin patch source for treatment of non-melanoma skin cancer. A 177Lu skin patch source based on Nafion-115 membrane backbone containing 3.46 ± 0.01 mCi of activity was used. Activity measurement of the patch source was based on gamma ray spectrometry using a HPGe detector. The efficiencies of the HPGe detector were fitted using an orthogonal polynomial function. The absorbed dose rate to water at 5 µm depth in water was determined using an extrapolation chamber, EBT3 Gafchromic film and compared with Monte Carlo methods. The correction factors such as Bragg-Gray stopping power ratio of water-to-air and chamber wall material being different from water, needed to be applied on measurements for establishing the dose rate at 5 µm depth, were calculated using the Monte Carlo method. Absorbed dose rate at 5 µm depth in water (surface dose rate) measured using an extrapolation chamber and EBT3 Gafchromic film were 9.9 ± 0.7 and 8.2 ± 0.1 Gy h-1 mCi-1 respectively for the source activity of 3.46 ± 0.01 mCi. The surface dose rate calculated using the Monte Carlo method was 8.7 ± 0.2 Gy h-1 mCi-1, which agrees reasonably well with measurement. The measured dose rate per mCi offers scope for ascertaining treatment time required to deliver the dose for propitious therapeutic outcome. Additionally, on-axis depth dose and lateral dose profiles at 5 µm and 1 mm depth in water phantom were also calculated using the Monte Carlo method.

Distinctive transcriptome alterations of prefrontal pyramidal neurons in schizophrenia and schizoaffective disorder.

Schizophrenia is associated with alterations in working memory that reflect dysfunction of dorsolateral prefrontal cortex (DLPFC) circuitry. Working memory depends on the activity of excitatory pyramidal cells in DLPFC layer 3 and, to a lesser extent, in layer 5. Although many studies have profiled gene expression in DLPFC gray matter in schizophrenia, little is known about cell-type-specific transcript expression in these two populations of pyramidal cells. We hypothesized that interrogating gene expression, specifically in DLPFC layer 3 or 5 pyramidal cells, would reveal new and/or more robust schizophrenia-associated differences that would provide new insights into the nature of pyramidal cell dysfunction in the illness. We also sought to determine the impact of other variables, such as a diagnosis of schizoaffective disorder or medication use at the time of death, on the patterns of gene expression in pyramidal neurons. Individual pyramidal cells in DLPFC layers 3 or 5 were captured by laser microdissection from 36 subjects with schizophrenia or schizoaffective disorder and matched normal comparison subjects. The mRNA from cell collections was subjected to transcriptome profiling by microarray followed by quantitative PCR validation. Expression of genes involved in mitochondrial (MT) or ubiquitin-proteasome system (UPS) functions were markedly downregulated in the patient group (P-values for MT-related and UPS-related pathways were <10(-7) and <10(-5), respectively). MT-related gene alterations were more prominent in layer 3 pyramidal cells, whereas UPS-related gene alterations were more prominent in layer 5 pyramidal cells. Many of these alterations were not present, or found to a lesser degree, in samples of DLPFC gray matter from the same subjects, suggesting that they are pyramidal cell specific. Furthermore, these findings principally reflected alterations in the schizophrenia subjects were not present or present to a lesser degree in the schizoaffective disorder subjects (diagnosis of schizoaffective disorder was the most significant covariate, P<10(-6)) and were not attributable to factors frequently comorbid with schizophrenia. In summary, our findings reveal expression deficits in MT- and UPS-related genes specific to layer 3 and/or layer 5 pyramidal cells in the DLPFC of schizophrenia subjects. These cell type-specific transcriptome signatures are not characteristic of schizoaffective disorder, providing a potential molecular-cellular basis of differences in clinical phenotypes.

Ion induced dewetting of Au-Si on a SiO2 surface: composite nanodot evolution and wettability transition.

A nanodot array morphology gradually develops on SiO2 surface when a thin bi-layer of Au and Si undergoes ion irradiation. An increasing amount of gold silicide is detected as islands on the insulator surface evolve into nanodots as a function of increasing ion fluence. Different stages of evolution from islands to nanodots are found to be driven by the localized melting of Au along the ion-track and dewetting of the metal film. Dewetting is accompanied by sputter-erosion and mixing of Au and Si at the bi-layer interface due to ion energy deposition. Interestingly, a gradual transition in wettability of the surface from the hydrophilic to the hydrophobic one is observed with the growth of nanodots, which is correlated with the compositional variation. The experimental results indicate a route towards the controlled growth of composite nanodots on an insulator surface having hydrophobic properties using ion irradiation.

ß1-adrenoceptor expression on GABAergic interneurons in primate dorsolateral prefrontal cortex: potential role in stress-induced cognitive dysfunction.

Uncontrollable stress exposure impairs working memory and reduces the firing of dorsolateral prefrontal cortex (dlPFC) "Delay cells", involving high levels of norepinephrine and dopamine release. Previous work has focused on catecholamine actions on dlPFC pyramidal cells, but inhibitory interneurons may contribute as well. The current study combined immunohistochemistry and multi-scale microscopy with iontophoretic physiology and behavioral analyses to examine the effects of beta1-noradrenergic receptors (ß1-ARs) on inhibitory neurons in layer III dlPFC. We found ß1-AR robustly expressed on different classes of inhibitory neurons labeled by the calcium-binding proteins calbindin (CB), calretinin (CR), and parvalbumin (PV). Immunoelectron microscopy confirmed ß1-AR expression on the plasma membrane of PV-expressing dendrites. PV interneurons can be identified as fast-spiking (FS) in physiological recordings, and thus were studied in macaques performing a working memory task. Iontophoresis of a ß1-AR agonist had a mixed effect, increasing the firing of a subset and decreasing the firing of others, likely reflecting loss of firing of the entire microcircuit. This loss of overall firing likely contributes to impaired working memory during stress, as pretreatment with the selective ß1-AR antagonist, nebivolol, prevented stress-induced working memory deficits. Thus, selective ß1-AR antagonists may be helpful in treating stress-related disorders.

Computation of epistemic uncertainty due to limited data samples in small field dosimetry using Fuzzy Set Theory.

OBJECTIVE: To estimate the epistemic (or fuzzy) uncertainty, arising due to limited data samples in the measurement of the output factors (OFs) of the small fields using Fuzzy Set Theory (FST). METHODS: EBT3 film samples of size 50 × 50 mm2 were used for the measurement of the OF of stereotactic radiosurgery (SRS) cones of size 4, 6, 7.5, 10, 12.5 and 15 mm diameter, normalized with respect to the output of 100 × 100 mm2 open field size. Three measurements were done per cone/field size. Red color channel was chosen for the dosimetry purpose, net optical density (NOD) was converted to the dose using non-linear relation. To estimate the epistemic uncertainty associated with the measured OFs due to limited number of data samples, a triangular fuzzy number (TFN) was assumed as the fuzziness in the dose delivered by the individual SRS cone/field. Uncertainty in the OF was estimated by applying the Fuzzy Vertex Method (FVM). The membership functions of the OF were constructed for each cone size and the nature of the uncertainty in the OF of the cones was expressed in the terms of its fuzziness. For the sake of completeness of the study, the statistical uncertainty involved in the procedure has also been calculated. RESULTS: The statistical and fuzzy uncertainties in the measurement of OF of cones range from 3.28 to 6.25% and 2.58 to 5.44% respectively. The smallest cone of 4 mm has the largest values of statistical and fuzzy uncertainties. The membership functions of the OF for the studied cones were triangular in nature. CONCLUSION: The epistemic uncertainty arising due to limited number of data samples holds a significant fraction of the prescribed dose, and therefore, should not be ignored in the total uncertainty estimation. ADVANCES IN KNOWLEDGE: This study highlights the significance of epistemic component of measurement uncertainty arising out due to the insufficient/limited number of measurements of a quantity.

ESTIMATION OF UNCERTAINTY IN MEASUREMENT OF DOSE EQUIVALENT AT LABORATORY LEVEL USING CASO4 :Dy-BASED TLD BADGE SYSTEM IN INDIA.

The objective of this paper is to estimate the combined uncertainty in the measurement of dose equivalent at laboratory level using CaSO4:Dy-based thermoluminescent dosemeter badge system by including variations in the components of the system. The variability of performance of the system is analysed using random effects one way analysis of variance model. The model enables estimation of the overall variance of the performance of the sampled population. The population in the study comprises all possible indicated dose equivalents on irradiation of dosemeters to a specific dose equivalent and radiation quality. Coefficient of variation and combined uncertainty at 95% level of confidence in the measurement of Hp(10) due to S-Cs radiation quality are found to be 6.6 and 14.3%, respectively, at the dose level of 5.31 mSv. The above parameters in the measurement of in-use quantity, i.e. whole body dose or photon dose equivalent are found to be 7.4 and 16.4%, respectively. The performance of the monitoring system on relative response has been observed to be satisfactory. Various factors affecting the variability of performance of the system are identified for further improvement in coefficient of variation.

Numerical simulation of 222Rn profiling in an experimental chamber using CFD technique.

Measurement of indoor 222Rn concentration and interpretation of distribution patterns are important for inhalation dosimetry in occupational and residential areas. Experimental determination of 222Rn concentration distribution and estimation of inhalation doses depend on the underlying aspects such as calibration of the detectors, accuracy of the techniques etc. Therefore, 222Rn concentration distribution needs to be very well understood in a closed domain for the controlled studies. In the recent times, Computational fluid dynamics (CFD) technique has gained a lot of attention for the prediction and visualization of indoor 222Rn concentration profiles and their mixing ability in the domain. The present study aims to simulate the effect of forced mixing on the 222Rn concentration profile in a 22 m3 experimental chamber. This chamber is designed for carrying out the controlled experiments, calibration and inter-comparison studies of various types of 222Rn detectors. Effect of different parameters such as time, flow rates, fan-off and fan-on conditions have been studied on the transient response, extent of the air mixing patterns and subsequently on 222Rn concentration profile in the chamber. Further, Non uniformity index (NUI) is introduced as a measure of the uniformity of the distribution in the closed domain. NUI is estimated for different cases in order to efficiently interpret the effect of above mentioned parameters on 222Rn profile in the chamber. This study will be useful to represent the turbulent conditions in real indoor domains and occupational facilities as U-mines during calibration and inter-comparison exercises of different 222Rn detectors.

Investigation of 220Rn emanation and exhalation from soil samples of Larsemann Hills region, Antarctica.

In the present study, thoron exhalation flux density were measured in the soil samples collected around the Indian station namely Bharati (69° 24.41' S, 76° 11.72' E) and its nearby islands in the Larsemann hills region of Antarctica. Further, dependency of thoron mass emanation rate and emanation coefficient on the soil grain size was studied by segregating the soil samples into four different grain size groups: 50-100 µm, 100-200 µm, 200-500 µm and 500-1000 µm which showed that both of them follow a decreasing trend with increase in grain size. A comparison of measured mass emanation rate between different soil samples showed that it had a larger variation for the smaller grain size which eventually decreased as grain size increased while emanation coefficient was observed to be nearly constant for all the grain size groups. The variation in emanation coefficient with respect to mean grain size has been investigated and an empirical exponential model has been proposed for predicting emanation coefficient for different grain sizes.

INVESTIGATION OF APPLICABILITY OF PURE PROPANE GAS FOR MICRODOSIMETRY AT NEUTRON FIELDS: A MONTE CARLO STUDY.

Applicability of pure propane gas for microdosimetric measurements in neutron fields was investigated using the FLUKA Monte Carlo code. Monoenergetic neutrons in the energy range 1 keV-20 MeV and the ISO-neutron sources such as 241Am-Be, 241Am-B, 252Cf and 252Cf + D2O were considered in the present study. The tissue-equivalent proportional counter (TEPC) simulated in the study was LET-1/2 (by Far West Technology) with site sizes 1, 2 and 8 µm. The study demonstrates that for a given site size, the TEPC filled with tissue-equivalent propane and pure propane gases produce similar microdosimetric distributions when the density of pure propane gas is lowered appropriately. For the ISO-neutron sources, the density of propane gas requires scaling by a factor 0.85. For the monoenergetic neutrons, depending upon the neutron energy, the values of scaling factors are in the range of 0.58-0.93.

MONTE CARLO-BASED INVESTIGATION OF MICRODOSIMETRIC DISTRIBUTION OF HIGH ENERGY BRACHYTHERAPY SOURCES.

FLUKA-based Monte Carlo calculations were carried out to study microdosimetric distributions in air and in water for encapsulated high energy brachytherapy sources (60Co, 137Cs, 192Ir and 169Yb) by simulating a Tissue Equivalent Proportional Counter (Model LET1/2) having sensitive diameter of 1. 27 cm for a site size of 1 µm. The study also included microdosimetric distributions of bare sources. When the sources are in air, for a given source, the source geometry does not affect the y¯F and y¯D values significantly. When the encapsulated 192Ir, 137Cs and 60Co sources are in water, y¯F and y¯D values increase with distance in water which is due to degradation in the energy of photons. Using the calculated values of y¯D, relative biological effectiveness (RBE) was obtained for the investigated sources. When 60Co, 137Cs and 192Ir sources are in water, RBE increases from 1.03 ± 0.01 to 1.17 ± 0.01, 1.24 ± 0.01 to 1.46 ± 0.02 and 1.50 ± 0.01 to 1.75 ± 0.03, respectively, when the distance was increased from 3-15 cm, whereas for 169Yb, RBE is about 2, independent of distance in water.

Pretreatment Dose Verification in Volumetric Modulated Arc Therapy Using Liquid Ionization Chamber.

PURPOSE: The purpose of the present study was to evaluate the practicability of liquid ionization chamber (LIC) for pretreatment dose verification of the advanced radiotherapy techniques such as volumetric modulated arc therapy (VMAT). MATERIALS AND METHODS: The dosimetric characteristics of LIC such as repeatability, sensitivity, monitor unit linearity, dose rate dependence, angular dependence, voltage-current response, and output factors were investigated in 6 MV therapeutic X-ray beams. The LIC was cross-calibrated against 0.125-cc air-filled thimble ionization chamber. A dedicated dosimetry insert made up of Perspex to incorporate the LIC at proper location in the intensity-modulated radiation therapy thorax phantom was locally fabricated. The collection efficiency and ion recombination correction factor was determined using the two-dose rate method. Pretreatment dose verification measurement of VMAT treatment plans were carried out using the liquid ionization chamber as well as small volume (0.125 cc) air-filled thimble ionization chamber. The measured dose values by the two dosimeters and TPS calculated dose at a given point were compared. RESULTS: The relative percentage differences between the TPS calculated and measured doses were within ± 1.57% for LIC and ± 2.21% for 0.125 cc ionization chamber, respectively. CONCLUSIONS: The measured dose values by the two dosimeters and TPS calculated dose at a given point were found comparable suggesting that the LIC could be a good choice of dosimeter for pretreatment dose verification in VMAT.

STUDY OF EFFECT OF CONSECUTIVE HEATING ON THERMOLUMINESCENCE GLOW CURVES OF MULTI-ELEMENT TL DOSEMETER IN HOT GAS-BASED READER SYSTEM.

The objective of this paper is to study the effect of consecutive heating of TL elements of a thermoluminescence dosemeter (TLD) card in hot N2 gas-based TLD badge reader. The effect is studied by theoretical simulations of clamped heating profiles of the discs and resulting TL glow curves. The simulated temperature profile accounts for heat transfer to disc from hot gas as well as radiative and convective heat exchanges between the disc and the surrounding. The glow curves are simulated using 10 component glow peak model for CaSO4:Dy using the simulated temperature profile. The shape of the simulated glow curves and trend in total TL signal of the three discs were observed to match closely with the experimental observations when elevated surrounding temperature was considered for simulation. It is concluded that the readout (heating) of adjacent TLD disc affects the surrounding temperature leading to the changes in temperature profile of the next disc.

Ultraviolet and Infrared luminescent Au-rich nanostructure growth in SiO2 by burrowing and inverse Oswald ripening process.

We study the evolution of nanoparticle morphology through successive stages when Au-Si bilayer on SiO2 is irradiated with 500 keV Xe-ions and resulting luminescence in the UV, Visible and infrared range. An array of nanoscale island morphology is developed on the silica surface in the initial stage of evolution which undergoes gradual burrowing in the silica matrix accompanied by elongation of large ones in the direction of incident ions under cumulative ion irradiation. Burrowing is found to occur in order to minimize the surface free energy of the nanoparticles. Numerical simulation based on the unified thermal spike model shows formation of molten latent tracks due to ions energy release which drive the dewetting of the metal layer and further give mobility to nanoparticle atoms leading to burrowing in the later stage of evolution and elongation of large nanoparticles. Satellite nanoparticles are observed to grow around Au nanoparticles embedded in silica through nucleation of Au atoms dissolved in the matrix by incident ions. The varying diameters of the Au satellite nanoparticles seem to result in luminescence in the UV and infrared range. The observed structure may find application in surface enhanced Raman scattering, catalysis, and LEDs.

Phantom-Based Feasibility Studies on Phase-Contrast Mammography at Indian Synchrotron Facility Indus-2.

INTRODUCTION: Use of synchrotron radiation (SR) X-ray source in medical imaging has shown great potential for improving soft-tissue image contrast such as the breast. The present study demonstrates quantitative X-ray phase-contrast imaging (XPCI) technique derived from propagation-dependent phase change observed in the breast tissue-equivalent test materials. MATERIALS AND METHODS: Indian synchrotron facility (Indus-2, Raja Ramanna Centre of Advanced Technology [RRCAT]) was used to carry out phantom feasibility study on phase-contrast mammography. Different phantoms and samples, including locally fabricated breast tissue-equivalent phantoms were used to perform absorption and phase mode imaging using 12 and 16 keV SR X-ray beam. Edge-enhancement index (EEI) and edge enhancement to noise ratio (EE/N) were measured for all the images. Absorbed dose to air values were calculated for 12 and 16 keV SR X-ray beam using the measured SR X-ray photon flux at the object plane and by applying the standard radiation dosimetry formalism. RESULTS AND CONCLUSION: It was observed in case of all the phantoms and test samples that EEI and EE/N values are relatively higher for images taken in the phase mode. The absorbed dose to air at imaging plane was found to be 75.59 mGy and 28.9 mGy for 12 and 16 keV SR energies, respectively. However, these dose values can be optimized by reducing the image acquisition time without compromising the image quality when clinical samples are imaged. This work demonstrates the feasibility of XPCI in mammography using 12 and 16 keV SR X-ray beams.

MEASUREMENT OF OPERATIONAL QUANTITIES Hp(0.07) AND Hp(3) FOR INDIGENOUSLY DEVELOPED 106Ru/106Rh SOURCE USING AN EXTRAPOLATION CHAMBER.

In the present study, a prototype 106Ru/106Rh source was fabricated using high level liquid waste from reactor fuel, fixed in a stainless steel housing with a window and backing made of silver. The study involves measurement of the operational quantities Hp(0.07), Hp(3) and the percentage depth dose (PDD) using an extrapolation chamber. It also involves determination of necessary correction factors to arrive at Hp(0.07) and Hp(3) following International Organisation for Standardisation (ISO) and methods suggested in literature. The study facilitates incorporation of the 106Ru/106Rh source as a beta reference source for quality assurance programme in TLD personnel monitoring as per the guidelines of ISO.

Maximum likelihood estimates of mean and variance of occupation radiation doses subjected to minimum detection levels.

Data collection and its analysis in the field of nuclear safety is an important task in the sense that it powers the improvement of safety as well as reliability of the plant. Thus, occupational exposure data analysis is presented to measure the safety or reliability of radiation protection of a given facility. It also is required as a basic input in making decisions on radiation protection regulations and recommendations. A common practice in radiation protection is to record a zero for observation below minimum detection limit (MDL) doses, which leads to an underestimation of true doses and overestimation of the dose-response relationship. Exposure data (both external and internal) are collected by monitoring each individual and this kind of monitoring generally is graded as low-level monitoring. So, in such low-level monitoring, the occurrence of exposure below MDL invites statistical complications for estimating mean and variance because the data are generally censored, i.e observations below MDL are marked. In Type I censoring, the point of censoring (e.g. the detection limit) is 'fixed' a priori for all observations and the number of the censored observations varies. In Type II censoring, the number of censored observations is fixed a priori, and the point of censoring vary. The methodology generally followed in estimating mean and variance with these censored data was the replacement of missing dose by half the MDL. In this paper, authors have used the maximum likelihood estimation (MLE) approach for the estimation of mean and standard deviation. A computer code BDLCENSOR has been developed in which all these MLE-based advanced algorithms are implemented. In addition to the MLE-based method, an expectation maximisation algorithm has also been implemented. The code is written using Visual BASIC 6.0. The paper describes the details of the algorithms adopted for handling such censored data to estimate bias free mean and standard deviation.

FLUKA-BASED MONTE CARLO INVESTIGATION OF MICRODOSIMETRIC DISTRIBUTIONS OF TELECOBALT BEAM.

FLUKA-based Monte Carlo calculations of microdosimetric distributions in water phantom involving a walled spherical Tissue-Equivalent Proportional Counter filled with tissue-equivalent propane gas have been studied for an indigenously developed telecobalt machine. The simulated site size considered in the study was 2 µm. In the Monte Carlo calculations, field size was varied from 10 cm × 10 cm to 35 cm × 35 cm and the depth was varied as 5-20 cm. The study also includes calculation of microdosimetric distributions with a 30° wedge filter. The efficiency of the calculations was improved up to a factor of 26 by choosing appropriate cut off values for production and transport of electrons. The calculated microdosimetric distributions of telecobalt machine is distinctly different from that of a bare 60Co source which is attributed to the influence of scattered photons from the machine head and the water phantom.

Effect of quantum confinement on lifetime of anharmonic decay of optical phonons in semiconductor nanostructures.

The anharmonic decay of phonons underlies many important effects in semiconductors, e.g. hotspot formation, phonon bottleneck and thermal resistivity. In this article, we evaluate the effect of quantum confinement on the anharmonic decay transition probability in a cubic isotropic material. This article focuses on the anharmonic decay of longitudinal optical phonons, generated from hot electrons, are directly related to formation of hotspots in the active region of semiconductor devices. The confinement effect has been realized in double interface heterostructure quantum well (DHSQW) (e.g. AlAs/GaAs/AlAs) and free-standing quantum well (FSQW) (e.g. GaAs) structures as the confined phonon modes have different properties inside the structures. The longitudinal-optical phonon decay rate is reduced for the case of a DHSQW compared to bulk material and for a FSQW the decay rate has a strong dependence on wavevector value of the three phonons involved.

Imaging and Dosimetric Study on Direct Flat-Panel Detector-Based Digital Mammography System.

INTRODUCTION: Image quality of digital mammography system is generally defined by three primary physical parameters, namely, contrast, resolution, and noise. Quantification of these metrics can be done by measuring objective image quality parameters defined as contrast-to-noise ratio (CNR), modulation transfer function (MTF), and noise power spectra (NPS). MATERIALS AND METHODS: In the present study, various imaging metrics such as CNR, contrast detail resolution, MTF, and NPS were evaluated for a direct flat-panel detector-based digital mammography system following the European Guidelines. Furthermore, system performance relating to both image quality and doses were evaluated using figure of merit (FOM) in terms of CNR2/mean glandular dose (MGD) under automatic exposure control (AEC) and clinically used OPDOSE operating mode. RESULTS AND CONCLUSION: Under AEC mode, FOM values for the 4.5 cm thick BARC polymethyl methacrylate (PMMA) phantom were found to be 15.02, 15.88, and 19.82 at Mo/Mo, Mo/Rh, and W/Rh target/filter (T/F), respectively. Under OPDOSE mode, FOM values were found to 65.32, 11.80, and 1.14 for the BARC PMMA phantom thickness of 2, 4.5, and 8 cm, respectively. Under OPDOSE mode, the calculated MGD values for three Computerized Imaging Reference Systems slab phantoms having total thickness of 7 cm were observed to be 3.03, 2.32, and 1.75 mGy with glandular/adipose tissue compositions of 70/30, 50/50, and 30/70, respectively, whereas for the 2-8-cm thick BARC PMMA phantom, the calculated MGDs were found to be in the range of 0.57-3.32 mGy. All the calculated MGDs values were found to be lower than the acceptable level of dose limits provided in European Guidelines.