Monte Carlo Evaluation of Dose Enhancement Due to CuATSM or GNP Uptake in Hypoxic Environments with External Beam Radiation.

PURPOSE: Most solid tumors contain areas of chronic hypoxia. Gold nanoparticles (GNP) have been extensively explored as enhancers of external beam radiation; however, GNP have lower cellular uptake in hypoxic conditions than under normoxic conditions. Conversely, the chelator diacetyl-bis (N(4)-methylthiosemicarbazonato) copper II (CuATSM) deposits copper in hypoxic regions, allowing for dose enhancement in previously inaccessible regions. METHODS: External beam sources with different spectra were modeled using a Monte Carlo code (EGSnrc) to evaluate radioenhancement in a layered model with metal solutions. Also considered was a simple concentric layered tumor model containing a hypoxic core with each layer varying in concentrations of either copper or gold according to hypoxic conditions. Low energy external photon beams were then projected onto the tumor to determine the regional dose enhancement dependent on hypoxic conditions. RESULTS: Dose enhancement was more pronounced for beam spectra with low energy photons (225 kVp) and was highly dependent on metal concentrations from 0.1 g/kg to 100 g/kg. Increasing the depth of the metallic solution layer from 1 cm to 6 cm decreased dose enhancement. A small increase in the dose enhancement factor (DEF) of 1.01 was predicted in the hypoxic regions of the tumor model with commonly used diagnostic concentrations of CuATSM. At threshold concentrations of toxic subcutaneous injection levels, the DEF increases to 1.02, and in simulation of a high concentration of CuATSM, the DEF increased to 1.07. High concentration treatments are also considered, as well as synergistic combinations of GNP/CuATSM treatments. CONCLUSION: The research presented is novel utilization of CuATSM to target hypoxic regions and act as a radiosensitizer by the nature of its ability to deposit copper metal in reduced tissue. We demonstrate CuATSM at high concentrations with low energy photons can increase dose deposition in hypoxic tumor regions.

Tritium Atom Exchange May Be Responsible for Activity Decrease in Plastic Liquid Scintillation Vials.

Detection and measurement of low-energy beta particles is commonly achieved by liquid scintillation counting, in particular for low-level tritium samples. When samples are contained in plastic scintillation vials for long-term storage, the tritium activity in the vials has been found to decrease faster than expected from its natural radioactive decay. Different explanations for this observation have attributed some of these tritium activity losses to diffusion of the sample, degradation of the LSC cocktail, and the potential long-term changes in quenching effects of the LSC cocktail. An alternative explanation may also be that the tritium organically binds to the carbon chains in the plastic bottle through direct H and H atom exchange. A study was designed and performed to test this latter hypothesis of H and H atom exchange in plastic. Deionized water was introduced in a plastic vial that previously contained tritiated water to assess any increase in tritium activity from the reverse atom exchange between the vial material and the deionized water. A greater loss in activity concentration is observed in plastic vials compared to glass vials as a function of storage time for the tritiated water. Furthermore, the tritium activity concentration in the deionized water increased when storage occurred in plastic vials, an effect that is not observed for storage in glass vials. The study results indicate that hydrogen atom exchange may possibly take place in plastic vials.

'Why' transforms information transfer into effective communication in radiological protection.

As scientists and professionals, we have been trained to present and lecture in front of an audience of similarly instructed peers, we subject our manuscripts to peer-review, and we mentor the next generation of radiological protection professionals to adopt the same methods of information transfer we equate with 'scientific communication.' The scientific community clearly has developed effective and efficient means to share progress in a given field of study. However, current efforts to improve our success in achieving public understanding of our most important and pertinent conclusions, and in communicating the 'risks' associated with low or moderate exposures to ionising radiation indicate the realisation that we have not been similarly successful in our interactions with the general public. We may be getting close to having exhausted our examples, comparisons, and metaphors. We realise that effective communication in radiological protection necessitates more than the transfer of information to the audience. Rather than concentrating solely on the source, the speaker, we also need to take into account the receiver, the audience. In addition to optimising speaker and presentation attributes, effective communication needs to address barriers to listening as well. We propose for the community's communication strategies to develop and include tools which allow us to communicate across a wide range of individual needs, attitudes, and interests in the audience. Effective communication in radiological protection needs to be tailored to the individuals in the audience to open channels for our transfer of information; it needs to 'catch' and 'capture' the audience for active listening. We first need to justify to the audience 'why' they should consider 'our facts,' before we can expect them to trust our recommendations on 'how' to respond to a given situation. Symbols and narratives then can help with the retention of the information received by the audience.

Developing Detection DecisioNS on the Absence or Presence of a Radiological Source using a Bayesian Interaction Model.

Bayesian statistics have been used in various health physics applications, but only limited material exists on the development of a decision threshold for simple gross count measurements using Bayesian statistics. Bayesian modeling specifies a logical procedure for processing information and provides the means to obtain abstract statistical knowledge about the data in question. A Bayesian interaction model was developed to analyze gross count measurements. This linear regression model studies the relationship between a gross count measurement and the standard deviation of the gross counts obtained in the current and the previous four measurements, and conditions the analysis on whether the data originate from background measurements or from measurements with a source present. The measure of that relationship is expressed statistically by the constructed parameter ζ, which in the Bayesian framework possesses a probability distribution that can be used to achieve detection decisions. The model was validated statistically and under operationally equivalent conditions. Specifically, it was applied to analyze sequential data obtained from continuous gross count measurements at fixed time intervals. The Bayesian analysis used five sequential measurements per detection decision. The model performs optimally for weaker source detections, and presents promising operational application. Its usefulness derives from the facts that an established training data set is not necessary, long-run background measurements are not required to establish parameter estimates, and ζ and the model are universally applicable such that their use is not limited to the predictor variable presented here.

Professional ethics in radiological protection.

Professionals in the field of radiological protection from sources of ionising radiation are subject to various codes of ethics published by the professional organisations and associations representing the community of radiological scientists and practitioners. The community and its individual members accept the codes' terms and conditions, and understand the professional consequences of non-compliance. However, while these codes of ethics may be prescriptive with respect to the general understanding of 'ethical behaviour' or 'professional conduct' of radiological protection professionals, they often provide little guidance on an ethical decision making process when conflicting interests and intentions require professional judgment. Radiological protection professionals serve as contractors to clients or advisers to employers, but are also expected to actively contribute to the radiological protection community and emphasise the welfare of and benefit to the general public. This paper summarises the philosophical approach to an ethical decision making process and attempts to clarify the role of the 'professional' in that process. It investigates the responsibilities, duties, and virtues of a radiological protection professional and explains the ethically prescribed position for the professional in the decision making process. Radiological protection professionals may not have the authority to render a binding decision, but their most ethical conduct may actually be in their intimate involvement in the development and execution of the final 'ethical decision' by providing guidance and counsel to the decision maker in a fiduciary professional-client relationship. The main pillars of a trusting professional-client relationship are the professional's integrity and communication skills.

Investigation of Dose Rates Exterior to an Above-Ground Waste Storage Facility Using Radiation Transport Models.

The dose rate profile at different heights above the ground and as a function of distance from the north, west, and south walls of an above-ground waste storage facility was analyzed using the Monte Carlo n-Particle Transport eXtended (MCNPX) radiation transport code. The waste storage facility houses 9,996 waste barrels of conditioned waste. The facility has concrete shielding added to the building walls on the north, west, and east sides, with no such additional shielding towards the roof or the south side wall; instead, the distance from the first row of barrels to the wall is extended to allow for maneuverability of a crane on the south side. The dose rate is computed as a function of distance using MCNPX and assuming a homogeneous Co distribution in each waste barrel. Different dose regions are identified and analyzed based on graphical features and best-fit functions. The dose rates were expected to be largest at the wall of the facility and subsequently decrease continuously with distance from the repository; however, our analysis indicates a peak in dose rate observed for all heights on the north and west sides of the facility. This peak is likely due to scattering in the shielding material and atmosphere, and possibly could be ascribed to skyshine. The difference between the dose rate at 1 m outside the wall and the peak dose rate is significant, and indicates that the dose rate measured close to the wall may not always be conservative for extended sources, such as an above-ground waste storage facility.

Fukushima-derived radionuclides in sediments of the Japanese Pacific Ocean coast and various Japanese water samples (seawater, tap water, and coolant water of Fukushima Daiichi reactor unit 5).

We investigated Ocean sediments and seawater from inside the Fukushima exclusion zone and found radiocesium (134Cs and 137Cs) up to 800 Bq kg-1 as well as 90Sr up to 5.6 Bq kg-1. This is one of the first reports on radiostrontium in sea sediments from the Fukushima exclusion zone. Seawater exhibited contamination levels up to 5.3 Bq kg-1 radiocesium. Tap water from Tokyo from weeks after the accident exhibited detectable but harmless activities of radiocesium (well below the regulatory limit). Analysis of the Unit 5 reactor coolant (finding only 3H and even low 129I) leads to the conclusion that the purification techniques for reactor coolant employed at Fukushima Daiichi are very effective.

Simultaneous Source Detection and Analysis Using a Zero-inflated Count Rate Model.

This paper proposes a novel Bayesian technique that allows for simultaneous source detection and count rate analysis. The technique involves using priors, which include a finite probability that the source count rate is exactly zero. Such priors are called "zero-inflated." Solving the posterior distribution of a zero-inflated count rate model provides the probability that the sample contains a source and a probability distribution for the source count rate if the source exists, without the need to perform redundant computations. Sampling from zero-inflated distributions is straightforward and can be accomplished with easily accessible open source software. In addition, zero-inflated priors lead to finite posterior probabilities of "no source," which is an easy-to-understand and satisfying result.

Efficacy of common decontamination methods for cleaning contaminated wounds.

Emergency preparedness and response for work with hazardous materials, including radiological materials, necessarily have to involve injuries sustained by the workers. Removing radionuclide contamination from wounds in tissue is essential to minimizing the intake of radiological materials and the internal dose to the individual. This study compares the efficacy of common decontamination methods for removal of Co from contaminated wounds inflicted in pig tissue. The decontamination procedures investigated include a commercially available, non-prescription, surfactant-based, non-ionic wound cleanser spray; a physiologic saline solution spray; and a physiologic saline solution pour. Three different types of wounds are examined: smooth incision, jagged cut, and blunt force trauma wounds. The cleanser and saline sprays are more effective at decontaminating all three wounds than the saline pour. Within the statistical limitations of the study, the difference between the cleanser spray and the saline spray is not significant. However, the cleanser spray successfully decontaminates the wound to a lower mean value. The most noticeable impact in the decontamination process appears to be due to the spray pressure employed with the cleanser and saline sprays.

Bayesian analysis of energy and count rate data for detection of low count rate radioactive sources.

A particle counting and detection system is proposed that searches for elevated count rates in multiple energy regions simultaneously. The system analyzes time-interval data (e.g., time between counts), as this was shown to be a more sensitive technique for detecting low count rate sources compared to analyzing counts per unit interval (Luo et al. 2013). Two distinct versions of the detection system are developed. The first is intended for situations in which the sample is fixed and can be measured for an unlimited amount of time. The second version is intended to detect sources that are physically moving relative to the detector, such as a truck moving past a fixed roadside detector or a waste storage facility under an airplane. In both cases, the detection system is expected to be active indefinitely; i.e., it is an online detection system. Both versions of the multi-energy detection systems are compared to their respective gross count rate detection systems in terms of Type I and Type II error rates and sensitivity.

Characterisation of non-constant background in counting measurements.

A 'moving-target' method for characterising background in a counting measurement in which the instantaneous background count rate is a function of time, rather than being fixed, is proposed. This model treats the average Poisson mean in observation period P as coming from a gamma distribution with parameters αP and ßP. This model is applied to a large dataset of replicate observations, consisting of 242 (234)U method blank measurements collected over a 2-y period. Point estimates of the model parameters are determined by comparing the mean and variance of the observed data and by maximising the likelihood function. Posterior distributions of the parameters are obtained by Markov Chain Monte Carlo. Assuming time-invariant fluctuations of the background count rate, the variation of the instantaneous count rate is described by a correlation function, which can be interpreted as describing how rapidly the background changes with time, or how likely the background is to change between measurements. An 'exponential-correlation' model of background time dependence is proposed, with parameters α, ß and correlation time τ. Once determined, these parameters fully describe the distribution of background, just as NB and TB in the fixed-target model.

Measurement of the tritium concentration in the fractionated distillate from environmental water samples.

Standard procedures for the measurement of tritium in water samples often require distillation of an appropriate sample aliquot. This distillation process may result in a fractionation of tritiated water and regular light water due to the vapor pressure isotope effect, introducing either a bias or an additional contribution to the total tritium measurement uncertainty. The current study investigates the relative change in vapor pressure isotope effect in the course of the distillation process, distinguishing it from and extending previously published measurements. The separation factor as a quantitative measure of the vapor pressure isotope effect is found to assume values of 1.04 ± 0.036, 1.05 ± 0.026, and 1.07 ± 0.038, depending on the vigor of the boiling process during distillation of the sample. A lower heat setting in the experimental setup, and therefore a less vigorous boiling process, results in a larger value for the separation factor. For a tritium measurement in water samples where the first 5 mL are discarded, the tritium concentration could be underestimated by 4-7%.

Comparison of the Chernobyl and Fukushima nuclear accidents: a review of the environmental impacts.

The environmental impacts of the nuclear accidents of Chernobyl and Fukushima are compared. In almost every respect, the consequences of the Chernobyl accident clearly exceeded those of the Fukushima accident. In both accidents, most of the radioactivity released was due to volatile radionuclides (noble gases, iodine, cesium, tellurium). However, the amount of refractory elements (including actinides) emitted in the course of the Chernobyl accident was approximately four orders of magnitude higher than during the Fukushima accident. For Chernobyl, a total release of 5,300 PBq (excluding noble gases) has been established as the most cited source term. For Fukushima, we estimated a total source term of 520 (340-800) PBq. In the course of the Fukushima accident, the majority of the radionuclides (more than 80%) was transported offshore and deposited in the Pacific Ocean. Monitoring campaigns after both accidents reveal that the environmental impact of the Chernobyl accident was much greater than of the Fukushima accident. Both the highly contaminated areas and the evacuated areas are smaller around Fukushima and the projected health effects in Japan are significantly lower than after the Chernobyl accident. This is mainly due to the fact that food safety campaigns and evacuations worked quickly and efficiently after the Fukushima accident. In contrast to Chernobyl, no fatalities due to acute radiation effects occurred in Fukushima.

Clearance monitoring using hand-held devices: operational implementation and challenges.

Clearance monitoring includes all measures taken and measurements performed to ensure that all pertinent regulatory conditions are met for clearance of waste material. For bulk material, only a limited number of monitoring techniques are feasible for providing the necessary proof of compliance in the time frames and at costs commensurate with operator and regulator expectations for decommissioning projects. Operationally, measurements using hand-held devices, such as contamination monitors using scintillator or proportional counter technology, might provide sufficiently short response times at acceptable accuracies to segregate the waste streams according to their level of contamination and allowing for a decision on their further processing. Recognizing the various limitations hand-held devices might display in bulk material screening during clearance monitoring measurements, the detection limits with respect to material self-attenuation and non-homogenous activity distributions have been investigated.

A plan for the handling of externally contaminated livestock.

Nuclear accidents and access to radiological weapons for terrorist organizations and countries with hostile intentions towards the United States are realistic scenarios in the current global landscape. A dispersion of radionuclides can result from a nuclear weapon detonation or from a nuclear accident occurring in facilities handling or using radioactive material, such as nuclear power reactors. Any target of a radiological dispersal device (RDD) or an attack with a nuclear weapon and the surrounding area of a reactor accident could be subject to a significant amount of fallout and radioactive contamination. Therefore, a nuclear event in close proximity to agricultural areas will cause significant concern regarding the contamination of food products. In order to respond quickly and effectively to a large amount of contaminated agricultural products, such as livestock, a prepared and effective plan for handling and processing of these products is necessary. A protocol outlining the evaluation of and procedures for handling and processing radioactively contaminated livestock is proposed, to ensure safe animal food production and economic stability in the livestock industry in the wake of such a nuclear or radiological event. An evaluation of the salvageability of the contaminated livestock is performed based on the degree of exposure, the cost of decontamination, expected demand for food products, and economic impact to the owner/producer. Important factors that impact the salvageability of affected livestock are listed and analyzed to support the decision process for handling contaminated animals.