Treatment verification and in vivo dosimetry for total body irradiation using thermoluminescent and semiconductor detectors

The objective of this work is the characterization of thermoluminescent and semiconductor detectors and their applications in treatment verification and in vivo dosimetry for total body irradiation (TBI) technique. Dose measurements of TBI treatment simulation performed with thermoluminescent detectors inserted in the holes of a “Rando anthropomorphic phantom” showed agreement with the prescribed dose. For regions of the upper and lower chest where thermoluminescent detectors received higher doses it was recommended the use of compensating dose in clinic. The results of in vivo entrance dose measurements for three patients are presented. The maximum percentual deviation between the measurements and the prescribed dose was 3.6%, which is consistent with the action level recommended by the International Commission on Radiation Units and Measurements (ICRU), i.e., ±5%. The present work to test the applicability of a thermoluminescent dosimetric system and of a semiconductor dosimetric system for performing treatment verification and in vivo dose measurements in TBI techniques demonstrated the value of these methods and the applicability as a part of a quality assurance program in TBI treatments.     

In-phantom dose verification of prostate IMRT and VMAT deliveries using plastic scintillation detectors

The goal of this work was to demonstrate the feasibility of using a plastic scintillation detector (PSD) incorporated into a prostate immobilization device to verify doses in vivo delivered during intensity-modulated radiation therapy (IMRT) and volumetric modulated-arc therapy (VMAT) for prostate cancer. The treatment plans for both modalities had been developed for a patient undergoing prostate radiation therapy. First, a study was performed to test the dependence, if any, of PSD accuracy on the number and type of calibration conditions. This study included PSD measurements of each treatment plan being delivered under quality assurance (QA) conditions using a rigid QA phantom. PSD results obtained under these conditions were compared to ionization chamber measurements. After an optimal set of calibration factors had been found, the PSD was combined with a commercial endorectal balloon used for rectal distension and prostate immobilization during external beam radiotherapy. This PSD-enhanced endorectal balloon was placed inside of a deformable anthropomorphic phantom designed to simulate male pelvic anatomy. PSD results obtained under these so-called “simulated treatment conditions” were compared to doses calculated by the treatment planning system (TPS). With the PSD still inserted in the pelvic phantom, each plan was delivered once again after applying a shift of 1 cm anterior to the original isocenter to simulate a treatment setup error.The mean total accumulated dose measured using the PSD differed the TPS-calculated doses by less than 1% for both treatment modalities simulated treatment conditions using the pelvic phantom. When the isocenter was shifted, the PSD results differed from the TPS calculations of mean dose by 1.2% (for IMRT) and 10.1% (for VMAT); in both cases, the doses were within the dose range calculated over the detector volume for these regions of steep dose gradient. Our results suggest that the system could benefit prostate cancer patient treatment by providing accurate in vivo dose reports during treatment and verify in real-time whether treatments are being delivered according to the prescribed plan.     

Characterization of a Ce3+ doped SiO2 optical dosimeter for dose measurements in HDR brachytherapy

Aim of this work was to study the application of a new miniaturized Ce³⁺ doped SiO₂ scintillation detector to in vivo dosimetry in high dose rate brachytherapy. Energy, dose-rate, temperature and angular dependences of the detector response to ¹⁹²Ir HDR brachytherapy fields were investigated, as well as sensitivity reproducibility and linearity. To this aim, two ad hoc phantoms were designed and developed to perform measurements in water. Intra-session reproducibility resulted to be very high, however inter-session reproducibility showed too high statistical variation. Detector response resulted to increase linearly with dose (R² = 0.997), with no evidence of energy and dose-rate dependence. Sensitivity resulted to increase linearly with temperature (R² = 0.995), with a 0.2% increase each °C. Finally, no significant angular dependence for the source moving around a circle in the azimuthal plane centered at the scintillator was observed. The obtained results show that the proposed detector is suitable for in vivo real-time dosimetry in high dose rate brachytherapy.     

A preliminary study of the performance of a novel design of multi-element tissue equivalent proportional counter for neutron monitoring

In this study we investigate the dependence of the sensitivity of a TEPC upon its surface area and demonstrate that a compact multi-element tissue equivalent proportional counter (METEPC) has a counting sensitivity comparable to a commercially available 12.7 cm (5 inch) diameter spherical TEPC. The METEPC incorporates 61 cylindrical counting volumes of internal diameter of 0.5 cm and height 5 cm, machined in a single block of tissue equivalent plastic. It is the simplest design available in the multi-element geometrical configuration and is approximately nine times smaller in volume than that of a conventional 12.7 cm spherical TEPC. The neutron sensitivity of commercially available TEPCs and the METEPC simulating a 2 μm tissue site size was examined experimentally using the McMaster University 1.25 MV double stage Tandetron accelerator, which produces low energy neutrons via the ⁷Li(p, n)⁷Be reaction. The mean energy of the neutron beams produced ranged from 34 keV to 354 keV. The results presented in this study suggests that the compact METEPC is able to produce measurements in low dose rate radiation environments with the same precision in a given length of time as could be obtained with a 12.7 cm diameter spherical TEPC.     

Evaluation of internal occupational exposure by 123I in a radiopharmaceutical production facility

¹²³I is a photon emitter radionuclide (159 keV) used for diagnostic procedures of endocrinal diseases in nuclear medicine. Since 1998 it is produced at the industrial radiopharmaceutical plant operated by the Institute for Nuclear Energy (IEN-CNEN) and supplied to clinics located in the State of Rio de Janeiro, in Brazil. The production of this radionuclide represents a risk of internal occupational exposure. According to international recommendations, workers involved in this activity should be routinely monitored in order to comply with dose limits and keep individual exposures as low and reasonably achievable. The Radiation Protection Plan implemented at the IEN includes annual in vivo measurements of ¹²³I in the thyroid performed at the In Vivo Monitoring Laboratory of the Institute for Radiation Protection and Dosimetry (IRD-CNEN). This work describes a series of improvements on the measurement techniques used for the monitoring of the workers from the facility, including (i) optimization of in vivo measurement of the thyroid using an array of high-purity germanium detectors, (ii) development of a new in vitro bioassay method for the determination of ¹²³I in urine samples using a HPGe germanium detector and (iii) the establishment of a methodology for internal dose assessment, based on bioassay data. The sensitivity of the methods allow detection of ¹²³I activities below derived registry level of 1 mSv for the incorporation scenarios of exposure assumed in this work. Thus, it can be concluded that the methods are suitable for application in routine monitoring of workers occupationally exposed to ¹²³I in this facility.     

The spatial distribution of thermal and epithermal neutrons in a graphite moderated spallation neutron field

The Gamma-3 assembly is located at the Joint Institute for Nuclear Research, Dubna, Russia. It consists of a cylindrical lead target (ø = 8 cm, L = 58.8 cm) surrounded by reactor grade graphite (110 × 110 × 60 cm). The target was irradiated with a beam of 1.6 GeV deuterons from the Nuclotron accelerator and CR-39 track detectors coupled to LR-115 2B film were used to measure the slow neutron distribution on the surface of the graphite. The detection efficiency of the CR-39 in the CR-39/LR-115 2B system was measured using a custom made calibration setup and found to be (1.12 ± 0.05) × 10⁻³ and (6.1 ± 1.2) × 10⁻⁴ tracks per neutron, for thermal and epithermal neutrons respectively, under the etching and counting procedures described in this work. The irradiation of the Gamma-3 was also simulated using MCNPX 2.7 Monte Carlo code and good agreement between the experimental and calculated track densities was found. This serves as a good validation for the computational models used to simulate spallation neutron production, transport and moderation.     

Application of liquid scintillation inclusion techniques for the simultaneous determination of alpha and beta activities in composite samples – A preliminary study

Present work highlights liquid scintillation inclusion techniques as a tool for simultaneous determination of gross α and β activities in composite samples. This preliminary study comprises a preamble exercise to check whether Automatic Efficiency Control (AEC) and knee point inclusion techniques which are conventionally used for analysis of two β-emitting radio-nuclides in a mixture, can be implemented for quantification of gross α and β activities in composite samples. In inclusion techniques, two counting regions are set such that there are spill-up and spill-down of pulse events in each region from both types of radio-nuclides. AEC which is built-in feature in Packard Tri-Carb 2900 TR Liquid Scintillation Counter (LSC) provides automatic counting region adjustments for single and dual label samples according to the degree of quench present in sample. While knee point inclusion technique requires manual Lower Level (LL) and Upper Level (UL) discriminator setting to define two counting regions. In the present study, α/β spiked composite samples were treated as dual label samples with α and β radio-nuclides as two distinct entities contributing to the gross activities and analyzed employing AEC and knee point inclusion techniques. Instrument discriminator settings and regions of interest (ROI) were evaluated to determine optimum counting conditions for both the techniques. Three sets of pure alpha and pure beta standards simulating the activity concentrations of real samples in terms of α/β activity ratios were used to calibrate LSC. Calibration methodology for Packard Tri-Carb 2900 TR LSC with respect to the above measurements using ²⁴¹Am, ³⁶Cl and ⁹⁰Sr/⁹⁰Y calibration standards is explained in detail. The practicability and working performance of these techniques was checked by the validation trials with spiked synthetic samples covering range of α/β activity ratios from 1:1 to 1:50 and 50:1. Procedures have been tested by comparison with, established PSA technique and repeatability has been evaluated.     

Transverse relaxation of cerebrospinal fluid depends on glucose concentration

PurposeTo evaluate the biophysical processes that generate specific T₂ values and their relationship to specific cerebrospinal fluid (CSF) content.Materials and methodsCSF T_2s were measured ex vivo (14.1 T) from isolated CSF collected from human, rat and non-human primate. CSF T_2s were also measured in vivo at different field strength in human (3 and 7 T) and rodent (1, 4.7, 9,4 and 11.7 T) using different pulse sequences. Then, relaxivities of CSF constituents were measured, in vitro, to determine the major molecule responsible for shortening CSF T₂ (2 s) compared to saline T₂ (3 s). The impact of this major molecule on CSF T₂ was then validated in rodent, in vivo, by the simultaneous measurement of the major molecule concentration and CSF T₂.ResultsEx vivo CSF T₂ was about 2.0 s at 14.1 T for all species. In vivo human CSF T₂ approached ex vivo values at 3 T (2.0 s) but was significantly shorter at 7 T (0.9 s). In vivo rodent CSF T₂ decreased with increasing magnetic field and T₂ values similar to the in vitro ones were reached at 1 T (1.6 s). Glucose had the largest contribution of shortening CSF T₂ in vitro. This result was validated in rodent in vivo, showing that an acute change in CSF glucose by infusion of glucose into the blood, can be monitored via changes in CSF T₂ values.ConclusionThis study opens the possibility of monitoring glucose regulation of CSF at the resolution of MRI by quantitating T₂.     

Temperature dependence of a Ce3+ doped SiO2 radioluminescent dosimeter for in vivo dose measurements in HDR brachytherapy

Fiber-optic-coupled scintillation dosimeters are characterized by their small active volume if compared to other existing systems, and are therefore particularly suited for internal in vivo dosimetry. Due to possible differences between calibration conditions (i.e., room temperature) and conditions of clinical application (i.e., body temperature), their temperature dependence should be accurately studied. In this work, the temperature dependence of a Ce³⁺ doped SiO₂ scintillation detector coupled to a SiO₂ optical fibre was investigated for high dose rate brachytherapy applications. To this aim, two sets of irradiations with two different Ir-192 sources were performed in a water bath phantom at water temperatures ranging between 17 °C and 40.4 °C (Experiment 1). The relative response of the dosimeter was collected and analyzed. The same experiment was repeated with a second optical fibre which was designed without the active Ce³⁺ doped part at its end (Experiment 2) as well as by changing the length of the passive fibre inserted in water (Experiment 3). The two sets of measurements of experiment 1 were in accordance, indicating a linear increase with temperature of the scintillator sensitivity, with an average increase of 0.27 ± 0.2%/°C. In experiment 2, a 0.5%/°C increase of the collected signal resulted for the passive fibre. No significant difference of the temperature coefficient was found by changing the length of the fibre inserted in water (experiment 3). The obtained results show that a temperature-specific correction factor should be adopted at temperatures different than room temperature (e.g. for in vivo internal dosimetry). Further studies are required to understand the observations.     

<Emphasis FontCategory="NonProportional">TauSpinner</Emphasis> program for studies on spin effect in tau production at the LHC

Final states involving tau leptons are important components of searches for new particles at the Large Hadron Collider (LHC). A proper treatment of tau spin effects in the Monte Carlo (MC) simulations is important for understanding the detector acceptance as well as for the measurements of tau polarization and tau spin correlations. In this note we present a TauSpinner package designed to simulate the spin effects. It relies on the four-momenta of the taus and their decay products, which are available both in simulated and experimental data. The flavor and the four-momentum of the boson decaying to the τ ⁻ τ ⁺ or τ ^± ν pair need to be known. In the Z/γ ^∗ case the initial state quark configuration is attributed from the intermediate boson kinematics, and the parton distribution functions (PDF’s). TauSpinner is the first algorithm suitable for emulation of tau spin effects in tau-embedded samples. It is also the first tool that offers the user the flexibility to simulate a desired spin effect at the analysis level. An algorithm to attribute tau helicity states to a previously generated sample is also provided.     

Mapping phosphorylation rate of fluoro-deoxy-glucose in rat brain by F chemical shift imaging

¹⁹F magnetic resonance spectroscopy (MRS) studies of 2-fluoro-2-deoxy-d-glucose (FDG) and 2-fluoro-2-deoxy-d-glucose-6-phosphate (FDG-6P) can be used for directly assessing total glucose metabolism in vivo. To date, ¹⁹F MRS measurements of FDG phosphorylation in the brain have either been achieved ex vivo from extracted tissue or in vivo by unusually long acquisition times. Electrophysiological and functional magnetic resonance imaging (fMRI) measurements indicate that FDG doses up to 500 mg/kg can be tolerated with minimal side effects on cerebral physiology and evoked fMRI-BOLD responses to forepaw stimulation. In halothane-anesthetized rats, we report localized in vivo detection and separation of FDG and FDG-6P MRS signals with ¹⁹F 2D chemical shift imaging (CSI) at 11.7 T. A metabolic model based on reversible transport between plasma and brain tissue, which included a non-saturable plasma to tissue component, was used to calculate spatial distribution of FDG and FDG-6P concentrations in rat brain. In addition, spatial distribution of rate constants and metabolic fluxes of FDG to FDG-6P conversion were estimated. Mapping the rate of FDG to FDG-6P conversion by ¹⁹F CSI provides an MR methodology that could impact other in vivo applications such as characterization of tumor pathophysiology.     

Monte Carlo investigation of the effect of small cutouts on beam profile parameters of 12 and 14 MeV electron beams

Cutouts, which are used as field-shaping shield, affect several electron beam parameters. These effects are more observable for small field sizes and high energy electron beams. Owing to the fact that small fields prevent the lateral scatter equilibrium, at higher energies larger field radius is required for the establishment of lateral equilibrium.The profile curves are derived from circular, triangular, and square cutout shapes and size placed in a 10 × 10 cm² electron applicator. These profile curves are obtained using parallel plane type ion chamber at the R₁₀₀, R₉₀, R₈₀ and R₅₀ depths. Correspondingly, the source surface distance is 100 cm.In this study MCNP Monte Carlo (MC) simulation was used to compare Percentage Depth Dose (PDD) and Profile of electron beams.Monte Carlo and measured results showed a good compliance for PDD and beam profile. The measurements and calculations showed that as the field width decreases, the Flatness and Penumbra Ratio also decreases. In other words, flatter plateau was available for larger fields. Also the Coverage Ratio for each of the profiles is presented. The flatness and symmetry values for triangle shapes were greater than the two other shapes.Knowledge of these changes are significant in radiation therapy. Accordingly, a comparison between the Monte Carlo data and the measured results can be beneficial for treatment simulation and development of treatment planning systems.     

Verification of radiotherapy doses by EPR dosimetry in patients' teeth

The aim of this work was to verify applicability of electron paramagnetic resonance (EPR) ex vivo dosimetry in teeth enamel for determination of doses absorbed by patients during radiotherapy with radiation fields covering head regions and to examine with what accuracy the doses predicted by radiotherapy treatment plan (RTP) can be confirmed by doses measured ex post by the EPR method. The doses were determined in 22 enamel samples obtained from 11 patients who, after their radiotherapy treatment underwent extraction of teeth due to medical reasons. The delivered doses were determined by measuring EPR signals in enamel samples from the extracted teeth; magnitude of these signals is proportional to concentration of stable free radicals induced by radiation in the hydroxyapatite content of enamel. The measured doses were compared with doses planned in the teeth locations by RTP systems. The relation between the measured (D_m) and the planned (D_p) doses can be described as a linear function: D_m = s·D_p + b, with the slope s = 0.93 ± 0.03 and the intercept b = 0.67 ± 1.26. The deviations between the measured and calculated doses were in the (−12.6%, +1.9%) range with the average deviation of – 4.6%. It is concluded, than more accurate measurements, achievable when using a higher calibration dose than in the present study, are necessary to confirm or to deny the observed bias between the measured and planned doses.     

Uncertainty evaluation of continuous noise sampling

An area of current interest and topic of multiple publications is the assessment of uncertainty in estimating long-term indicators from measurements made for periods of time of less than 1 year. In this work, these prior investigations have been used as a starting point.Based on measurements made during one whole year at 26 sampling points with variables of urban and traffic characteristics, it was considered two aims related to uncertainty in the estimation of the annual L_den. The strength of this study is the large amount of data, which allows to simulate real measurements by sampling data from random days. Thus, it was studied in detail the predictive ability of the expressions proposed in the literature. Associated with this objective, then it was sought to evaluate the uncertainty associated with the estimation of annual L_den when random days of sampling were much lower than a full year.The results indicate the need for further progress in the theoretical determination of uncertainty. Second, the results made it able to estimate the uncertainty for the L_den indicator based on the number days sampled randomly.     

Enhanced magnetocaloric effect in Eu-doped La0.7Ca0.3MnO3 compounds

Orthorhombic La_0.7-xEu_xCa_0.3MnO₃ samples (x = 0.04–0.12) with apparent density of ρ = 3.9–4.1 g/cm³ prepared by solid-state reactions have been studied. The analysis of temperature-dependent magnetization for an applied field H = 500 Oe indicated a decrease of the Curie temperature (T_C) from about 225 K for x = 0.04 through 189 K for x = 0.08–146 K for x = 0.12. The magnetocaloric (MC) study upon analyzing M(H, T) data has revealed that the magnetic entropy change around T_C reaches the maximum (|ΔS_max|), which is dependent on both x and H. For an applied field interval of ΔH = 60 kOe, |ΔS_max| values are about 5.88, 4.93, and 4.71 J/kg⋅K for x = 0.04, 0.08, and 0.12, respectively. Though |ΔS_max| decreases with increasing x, relative cooling power (RCP) increases remarkably from 383 J/kg for x = 0.04 to about 428 J/kg for x = 0.08 and 0.12. This is related to the widening of the ferromagnetic-paramagnetic transition region when x increases. Particularly, if combining two compounds with x = 0.04 and 0.08 (or 0.12) as refrigerant blocks for MC applications, a cooling device can work in a large temperature range of 145–270 K, corresponding to RCP ≈ 640 J/kg for H = 60 kOe. M(H) analyses around T_C have proved x = 0.04 exhibiting the mixture of first- and second-order phase transitions while x = 0.08 and 0.12 exhibit a second-order nature. The obtained results show potential applications of Eu-doped La_0.7Ca_0.3MnO₃ materials for magnetic refrigeration below room temperature.     

The photocurrent response of human cones is fast and monophasic

Background  

The precise form of the light response of human cone photoreceptors in vivo has not been established with certainty. To investigate the response shape we compare the predictions of a recent model of transduction in primate cone photoreceptors with measurements extracted from human cones using the paired-flash electroretinogram method. As a check, we also compare the predictions with previous single-cell measurements of ground squirrel cone responses.     

Assembly of γ-Fe2O3/polyaniline nanofilms with tuned dipolar interaction

The internal morphology and magnetic properties of layer-by-layer assembled nanofilms of polyaniline (PANI) and maghemite (γ-Fe₂O₃—7.5-nm diameter) were probed with cross-sectional transmission electron microscopy (TEM) and magnetization measurements (magnetic hysteresis loops, magnetization using zero-field cooled/field-cooled protocols, and ac magnetic susceptibility). Additionally, simulations of the as-produced samples were performed to assess both the nanofilm’s morphology and the corresponding magnetic signatures using the cell dynamic system (CDS) approach and Monte Carlo (MC) through the standard Metropolis algorithm, respectively. Fine control of the film thickness and average maghemite particle–particle within this magnetic structure was accomplished by varying the number of bilayers (PANI/γ-Fe₂O₃) deposited onto silicon substrates or through changing the concentration of the maghemite particles suspended within the colloidal dispersion sample used for film fabrication. PANI/γ-Fe₂O₃ nanofilms comprising 5, 10, 25 and 50 deposited bilayers displayed, respectively, blocking temperatures (T _B) of 30, 35, 39 and 40 K and effective energy barriers (ΔE/k _B) of 1.0 × 10³, 2.3 × 10³, 2.8 × 10³ and 2.9 × 10³ K. Simulation of magnetic nanofilms using the CDS model provided the internal morphology to carry on MC simulation of the magnetic properties of the system taking into account the particle–particle dipolar interaction. The simulated (using CDS) surface–surface particle distance of 0.5, 2.5 and 4.5 nm was obtained for nanofilms with thicknesses of 36.0, 33.9 and 27.1 nm, respectively. The simulated (using MC) T _B values were 33.0, 30.2 and 29.5 K for nanofilms with thicknesses of 36.0, 33.9 and 27.1 nm, respectively. We found the experimental (TEM and magnetic measurements) and the simulated data (CDS and MC) in very good agreement, falling within the same range and displaying the same systematic trend. Our findings open up new perspectives for fabrication of magnetic nanofilms with pre-established (simulated) morphology and magnetic properties.     

Establishment of a method for measurement of gross alpha/beta activities in water from Vojvodina region

Very important part of environmental studies is the determination of the quality of drinking water, which often requires measuring of alpha and beta activity in analyzed water samples. The usual method for monitoring of low-level α and β radioactivity is to use gas-proportional detectors where ionization and proportional regions are used for α and β counting, respectively Simultaneous measurement of gross alpha and gross beta activities by liquid scintillation counting technique using Quantulus 1220 liquid scintillation counter (LSC) equipped with Pulse Shape Analyzer (PSA) is described. Water samples were prepared for measurements according to the ASTM D 7283-06 Standard Test Method. More than 50 samples of drinking water from Vojvodina region were measured. The data obtained can provide important information for the consumer regarding the preliminary dose exposure risk due to water intake.     

First-principles and Monte Carlo combinational study on Zn1−xCoxO diluted magnetic semiconductor

The electronic structures and magnetic properties of Zn_1−xCo_xO (x=5.55%,8.33%,12.5%) are studied using first-principles calculations in combination with Monte Carlo (MC) simulation. The combinational method makes possible a complete simulation from the microscopic magnetic interaction to macroscopic magnetic behavior. The calculated results from first principles indicate that the ferromagnetic ground state is stabilized by a half-metallic electronic structure which originates from the strong hybridization between Co 3d electrons and O 2p electrons. With the magnetic coupling strengths obtained from first-principles calculations, the MC simulation predicts the ferromagnetism of Zn_1−xCo_xO (x=5.55%,8.33%,12.5%) with , which is consistent with the experimental facts.     

Conductance of quantum interference transistors in parallel and in series

We theoretically study the electronic conductance G and the current–voltage characteristics of two quantum interference transistors in parallel and in series. We use two different definitions of conductance,G ∼ T and G ∼ T / R. Neither can reproduce the classical additivity law in the case of coherent transport due to quantum interference for the elements in series and quasibound states when elements are in parallel. In the case of two transistors in series, we find that the quantityT / R only qualitatively better represents the additivity law, which is probably expected because this model avoids counting the contact resistance twice. However, for the parallel configuration of transistors, the conductance is almost additive for the majority of energies when G ∼ T, except for the single-mode regime. Possible use of these configurations in digital electronics for basic logic functions is discussed.