Limitations in Predicting the Space Radiation Health Risk for Exploration Astronauts

Despite years of research, understanding of the space radiation environment and the risk it poses to long-duration astronauts remains limited. There is a disparity between research results and observed empirical effects seen in human astronaut crews, likely due to the numerous factors that limit terrestrial simulation of the complex space environment and extrapolation of human clinical consequences from varied animal models. Given the intended future of human spaceflight, with efforts now to rapidly expand capabilities for human missions to the moon and Mars, there is a pressing need to improve upon the understanding of the space radiation risk, predict likely clinical outcomes of interplanetary radiation exposure, and develop appropriate and effective mitigation strategies for future missions. To achieve this goal, the space radiation and aerospace community must recognize the historical limitations of radiation research and how such limitations could be addressed in future research endeavors. We have sought to highlight the numerous factors that limit understanding of the risk of space radiation for human crews and to identify ways in which these limitations could be addressed for improved understanding and appropriate risk posture regarding future human spaceflight.Comment: Accepted for publication by Nature Microgravity (2018

Beyond two-stage models for lung carcinogenesis in the Mayak workers: Implications for Plutonium risk

Mechanistic multi-stage models are used to analyze lung-cancer mortality after Plutonium exposure in the Mayak-workers cohort, with follow-up until 2008. Besides the established two-stage model with clonal expansion, models with three mutation stages as well as a model with two distinct pathways to cancer are studied. The results suggest that three-stage models offer an improved description of the data. The best-fitting models point to a mechanism where radiation increases the rate of clonal expansion. This is interpreted in terms of changes in cell-cycle control mediated by bystander signaling or repopulation following cell killing. No statistical evidence for a two-pathway model is found. To elucidate the implications of the different models for radiation risk, several exposure scenarios are studied. Models with a radiation effect at an early stage show a delayed response and a pronounced drop-off with older ages at exposure. Moreover, the dose-response relationship is strongly nonlinear for all three-stage models, revealing a marked increase above a critical dose

Knowledge, attitude and perception on radiation imaging among children's caregivers in the pediatric dental clinic

OBJECTIVE: Nuclear medicine provides important clinical information for diagnostic and therapeutic purposes. Use of medical imaging has gradually increased in the United States and this has raised health concerns about the potential future risks associated with radiation exposure in children. While studies have evaluated the adverse effects of imaging procedures, there is insufficient evidence about communicating radiation risks. The overall purpose of this paper is to review radiation risks in pediatric imaging using published evidence by the World Health Organization and to evaluate the knowledge and attitude of caregivers towards radiation risks in pediatric imaging. Specifically, we aim to determine whether an educational brochure improves parental knowledge of radiation and/or changes in attitude and perception to allow their children to undergo dental radiographs. METHODS: A prospective sample survey was performed of caregivers who presented with their child to the Boston University Pediatric Oral Healthcare Center. Parents or legal guardians (18 years or older) who accompanied a child were eligible for inclusion and approached for enrollment. Pre- and post-survey questionnaires were used to evaluate parents’ or guardians’ level of knowledge and attitude about the risks and benefits of dental radiographs. Parents were also asked their comfort level to allow their child to undergo dental radiographs. After completing the pre-survey questionnaire, parents were asked to read the English-language informational handout. Statistical analysis was performed through Microsoft Excel 2013. Descriptive analysis was conducted to summarize the survey responses. RESULTS: Among 30 parents who were surveyed, a small proportion (30%) of parents were very comfortable with dentist using dental radiographs on their child, versus 57% after reading the handout. Results showed that the informational handout improved the parental knowledge of risks and benefits of ionizing radiation. Most parents indicated that the handout was helpful and they reported increased level of comfort and willingness in their children receiving radiation imaging during dental treatment procedures. DISCUSSION: Educating parents or caregivers through an informational handout is a helpful resource in improving their knowledge and in relieving their concerns. Informing parents about the risks of ionizing radiation does not change parental willingness for their children to undergo dental radiographs

Radiation protection guidelines for space missions

NASA's current radiation protection guidelines date from 1970, when the career limit was set at 400 rem. Today, using the same approach, but with the current risk estimates, a considerably lower career limit would obtain. Also, there is considerably more information about the radiation environments to be experienced in different missions than previously. Since 1970 women have joined the ranks. For these and other reasons it was necessary to reexamine the radiation protection guidelines. This task was undertaken by the National Council on Radiation Protection and Measurements Scientific Committee 75 (NCRP SC 75). Below the magnetosphere the radiation environment varies with altitude and orbit inclination. In outer space missions galactic cosmic rays, with the small but important heavy ion component, determine the radiation environment. The new recommendations for career dose limits, based on lifetime excess risk of cancer mortality, take into account age at first exposure and sex. The career limits range from 100 rem (4.0Sv) for a 24 year old female to 400 rem for a 55 year old male compared to the previous single limit of 400 rem (4.0 Sv). The career limit for the lens of the eye was reduced from 600 to 400 rem (6.0 to 4.0 Sv.

Local DRLs and automated risk estimation in paediatric interventional cardiology

Introduction : Cardiac catheterization procedures result in high radiation doses and often multiple procedures are necessary for congenital heart disease patients. However, diagnostic reference levels (DRL) remain scarce. Our first goal was finding the optimal DRL parameter and determining appropriate DRLs. The second goal was to calculate organ doses (OD), effective doses (ED) and lifetime attributable risks (LAR) per procedure and to provide conversion factors based on dose area product (DAP). Materials and methods : DRLs are calculated for each procedure type, as the 75th percentile of the cumulative value per procedure from the corresponding parameter. All irradiation events in the DICOM Structured Reports were automatically processed and simulated using PCXMC, resulting in OD, ED and LAR. Using a Kruskal Wallis H test and subsequent pairwise comparisons, differences in median values of the DRL parameter between procedure types were assessed. Results : Linear regression showed a strong correlation and narrow confidence interval between DAP and product of body weight and fluoroscopy time (BWxFT), even when all procedures (diagnostic and interventional) are combined. Only 15% of the pairwise comparisons were statistically significant for DAP normalized to BWxFT (DAP(BWxFT)). The latter pairs contained less frequent procedure types with significant outliers. For DAP normalized to BW (DAP(BW)), 38% of the pairwise comparisons showed statistically significant differences. Conversion factors from DAP(BW) to OD and ED were reported for various weight groups, due to the higher correlation between DAP(BW) and both OD and ED than between DAP and both OD and ED. Conclusions : The P75 of DAP(BWxFT) for all procedures combined serves as an appropriate DRL value. This facilitates local DRL determination in smaller paediatric centres, which often have insufficient data to produce appropriate DRLs for different procedure types. Conversion factors are more reliable starting from DAP(BW) instead of DAP and should be used according to the appropriate BW group

LINEAR NO-THRESHOLD MODEL VS. RADIATION HORMESIS

The atomic bomb survivor cancer mortality data have been used in the past to justify the use of the linear no-threshold (LNT) model for estimating the carcinogenic effects of low dose radiation. An analysis of the recently updated atomic bomb survivor cancer mor- tality dose-response data shows that the data no longer support the LNT model but are consistent with a radiation hormesis model when a correction is applied for a likely bias in the baseline cancer mortality rate. If the validity of the phenomenon of radiation hormesis is confirmed in prospective human pilot studies, and is applied to the wider pop- ulation, it could result in a considerable reduction in cancers. The idea of using radiation hormesis to prevent cancers was proposed more than three decades ago, but was never investigated in humans to determine its validity because of the dominance of the LNT model and the consequent carcinogenic concerns regarding low dose radiation. Since cancer continues to be a major health problem and the age-adjusted cancer mortality rates have declined by only ~10% in the past 45 years, it may be prudent to investigate radiation hormesis as an alternative approach to reduce cancers. Prompt action is urged

Focal Spot, Summer 1997

https://digitalcommons.wustl.edu/focal_spot_archives/1076/thumbnail.jp

Blood cell gene expression profiles: A narrative review of biomarkers and effects of low-dose ionizing radiation exposure

Ionizing radiation (IR) is a ubiquitous environmental agent whose effects on organisms are well known. This review provides a summary about definitions and man-made low-dose ionizing radiation (LDIR) sources and dosimeters used in radiation protection. Moreover, the main purpose of this article was to overview the pro-oncogenic effects of LDIR, and to provide experimental evidence that reinforce the use of gene expression data as biomarkers of LDIR effects. Our review showed that basic studies on biological response to LDIR are considered priority. Further, understanding occupational exposure to LDIR may provide valuable information to organize the prevention and prevent from the onset of long-term health effects in radiation workers. Currently, the biodosimetry-based assessment in certain high risk occupational groups may be performed by using peripheral blood cells as samples for testing and validation of biomarkers specificity and sensitivity. Most of the studies on this topic are aimed at establishing new biomarkers and approaches to biological dosimetry, for allowing non-invasive monitoring of long-term health effects of LDIR. Analysis on changes in gene-expression, which is an early specific biological response to LDIR, could provide rapid estimates of individual dose in occupational cohorts, improving the management of periodical medical examination in subjects exposed to LDIR sources