Moderate Dose Rates Research Articles

Revealing the Increased Stress Response Behavior through Transcriptomic Analysis of Adult Zebrafish Brain after Chronic Low to Moderate Dose Rates of Ionizing Radiation

Simple SummaryThe increasing use of radiopharmaceuticals for medical diagnostics and radiotherapy raises concerns regarding health risks for both humans and the environment. Additionally, in the context of major nuclear accidents like in Chernobyl and Fukushima, very little is known about the effects of chronic exposure to low and moderate dose rates of ionizing radiation (IR). Many studies demonstrated the sensibility of the developmental brain, but little data exists for IR at low dose rates and their impact on adults. In this study, we characterized the molecular mechanisms that orchestrate stress behavior caused by chronic exposure to low to moderate dose rates of IR using the adult zebrafish model. We observed the establishment of a congruent stress response at both the molecular and individual levels.High levels of ionizing radiation (IR) are known to induce neurogenesis defects with harmful consequences on brain morphogenesis and cognitive functions, but the effects of chronic low to moderate dose rates of IR remain largely unknown. In this study, we aim at defining the main molecular pathways impacted by IR and how these effects can translate to higher organizational levels such as behavior. Adult zebrafish were exposed to gamma radiation for 36 days at 0.05 mGy/h, 0.5 mGy/h and 5 mGy/h. RNA sequencing was performed on the telencephalon and completed by RNA in situ hybridization that confirmed the upregulation of oxytocin and cone rod homeobox in the parvocellular preoptic nucleus. A dose rate-dependent increase in differentially expressed genes (DEG) was observed with 27 DEG at 0.05 mGy/h, 200 DEG at 0.5 mGy/h and 530 DEG at 5 mGy/h. Genes involved in neurotransmission, neurohormones and hypothalamic-pituitary-interrenal axis functions were specifically affected, strongly suggesting their involvement in the stress response behavior observed after exposure to dose rates superior or equal to 0.5 mGy/h. At the individual scale, hypolocomotion, increased freezing and social stress were detected. Together, these data highlight the intricate interaction between neurohormones (and particularly oxytocin), neurotransmission and neurogenesis in response to chronic exposure to IR and the establishment of anxiety-like behavior.

In-vivo and in-vitro impact of high-dose rate radiotherapy using flattening-filter-free beams on the anti-tumor immune response

IntroductionModern accelerators have the “flattening filter-free” (FFF) technique to deliver RT with a moderate high-dose rate, currently used in limited clinical indications. No scientifically established data are currently available on the possible effects of this high dose rate on the anti-tumor immune response. We therefore propose here to study these effects in a preclinical CT26 murine colorectal tumor model. Material and methodsIn-vitro, CT26 cells were irradiated on a Varian TrueBeam® linac at 3 different dose rates (4; 12 or 24 Gy/min) using the FFF mode. Activation of the anti-tumor immune response was evaluated by the analysis of induction of genes of the type I interferon pathway by RT-qPCR, and by the study of the induction of immunogenic death biomarkers. In-vivo, an efficacy study of RT delivering 16.5 Gy at 2 different dose rates was performed in immunocompetent Balb/c mice carrying CT26 syngeneic tumors, as well as an immunomonitoring analysed by flow cytometry and a transcriptomic analysis using RNA sequencing. Statistical analyzes were performed using non-parametric tests. ResultsIn-vitro, no significant influence of an increase in FFF dose rate was shown for the induction of genes of the type I interferon pathway as well as for the studied immunogenic death markers (HMGB1 secretion). In-vivo, no difference in terms of tumor growth retardation between the 2 dose rates used was demonstrated, as well as for the composition of immune cell infiltrates within tumor microenvironment and the expression of immune checkpoints in immunomonitoring and RNAseq. ConclusionIn this study involving the CT26 model, no influence of a moderate high dose rate in FFF technique on the anti-tumor immune response was demonstrated, which would make studies of associations between RT and checkpoint inhibitors fit with this technique of RT. However, further explorations using other cellular models seem to be of interest.

Ionising Radiation Induces Promoter DNA Hypomethylation and Perturbs Transcriptional Activity of Genes Involved in Morphogenesis during Gastrulation in Zebrafish.

Embryonic development is particularly vulnerable to stress and DNA damage, as mutations can accumulate through cell proliferation in a wide number of cells and organs. However, the biological effects of chronic exposure to ionising radiation (IR) at low and moderate dose rates (< 6 mGy/h) remain largely controversial, raising concerns for environmental protection. The present study focuses on the molecular effects of IR (0.005 to 50 mGy/h) on zebrafish embryos at the gastrula stage (6 hpf), at both the transcriptomics and epigenetics levels. Our results show that exposure to IR modifies the expression of genes involved in mitochondrial activity from 0.5 to 50 mGy/h. In addition, important developmental pathways, namely, the Notch, retinoic acid, BMP and Wnt signalling pathways, were altered at 5 and 50 mGy/h. Transcriptional changes of genes involved in the morphogenesis of the ectoderm and mesoderm were detected at all dose rates, but were prominent from 0.5 to 50 mGy/h. At the epigenetic level, exposure to IR induced a hypomethylation of DNA in the promoter of genes that colocalised with both H3K27me3 and H3Kme4 histone marks and correlated with changes in transcriptional activity. Finally, pathway enrichment analysis demonstrated that the DNA methylation changes occurred in the promoter of important developmental genes, including morphogenesis of the ectoderm and mesoderm. Together, these results show that the transcriptional program regulating morphogenesis in gastrulating embryos was modified at dose rates greater than or equal to 0.5 mGy/h, which might predict potential neurogenesis and somitogenesis defects observed at similar dose rates later in development.

In Vitro Wear Performance of X-ray Cross-Linked Vitamin E Blended Polyethylene

The most common radiation cross-linking methods are electron-beam and Gamma-irradiation. Gamma-irradiation has a very low dose rate and e-beam serious penetration limitations. X-ray exhibits an excellent penetration capacity with a moderate dose rate. The objective of the study was the investigation of the wear behavior of vitamin E blended Ultrahigh Molecular Weight Polyethylene highly cross-linked by X-ray as an alternative cross-linking technology. We hypothesized that using same dose and irradiation temperature the wear behavior would be equivalent regardless of the radiation source.Hip wear simulation was performed with five different polyethylene acetabular inserts articulating with 40 mm diameter cobalt‑chromium heads. Two X-ray doses of 80 and 100 kGy and two irradiation temperatures each, i.e. room temperature and 100 °C, were considered. The reference was Vitelene®, a vitamin E stabilized polyethylene cross-linked by e-beam with 80 kGy at 100 °C. The inserts were subjected to artificial aging for 2 weeks prior to test.Increasing both the dose and the irradiation temperature led to an improved wear performance.X-ray showed the ability to improve the wear resistance of polyethylene in the same range as e-beam, as both are ionizing irradiation. SignificanceHighly cross-linked polyethylene has been established and taken over 80–100% of polyethylene usage in Total Hip Arthroplasty [1–3]. The goal is to retain its mechanical properties, oxidative stability and superior wear resistance over time, which is crucial in order to reduce the incidence of periprosthetic osteolysis and increase the service time over the second implantation decade [4]. Vitamin E stabilized polyethylene has been successfully introduced showing very good results at 5 years [5–7]. X-ray irradiation stands out by its worthwhile characteristics like high penetration capacity and moderate dose rate which extend the treatment possibilities of polyethylene and the preservation of its properties in the long term.

Recombination in liquid filled ionisation chambers with multiple charge carrier species: Theoretical and numerical results

Liquid-filled ionisation chambers (LICs) are used in radiotherapy for dosimetry and quality assurance. Volume recombination can be quite important in LICs for moderate dose rates, causing non-linearities in the dose rate response of these detectors, and needs to be corrected for. This effect is usually described with Greening and Boag models for continuous and pulsed radiation respectively. Such models assume that the charge is carried by two different species, positive and negative ions, each of those species with a given mobility. However, LICs operating in non-ultrapure mode can contain different types of electronegative impurities with different mobilities, thus increasing the number of different charge carriers. If this is the case, Greening and Boag models can be no longer valid and need to be reformulated.In this work we present a theoretical and numerical study of volume recombination in parallel-plate LICs with multiple charge carrier species, extending Boag and Greening models. Results from a recent publication that reported three different mobilities in an isooctane-filled LIC have been used to study the effect of extra carrier species on recombination. We have found that in pulsed beams the inclusion of extra mobilities does not affect volume recombination much, a behaviour that was expected because Boag formula for charge collection efficiency does not depend on the mobilities of the charge carriers if the Debye relationship between mobilities and recombination constant holds. This is not the case in continuous radiation, where the presence of extra charge carrier species significantly affects the amount of volume recombination.

Synthesis of tailored nanogels by means of two-stage irradiation

A new method allowing to synthesize polymeric nanogels of independently chosen weight-average molecular weight (Mw) and dimensions in an additive-free system consisting only of linear macromolecules and water is described and tested. This approach, based on generation of free radicals using ionizing radiation in oxygen-free polymer solutions, consists of two steps. In the first step, semi-concentrated polymer solution is irradiated at a moderate dose rate, so that in the stationary state the average number of radicals per chain is <1. This promotes intermolecular cross-linking with increase in Mw and coil dimensions. When the desired Mw is reached, in the second step intra-molecular recombination is induced by pulse irradiation of dilute solution (with the average number of radicals per chain >1 after each pulse), leading to a decrease in nanogel diameter while keeping Mw nearly constant. Experimental data on a model polymer – poly(N-vinylpyrrolidone) – confirm that the proposed method allows synthesizing nanogels of desired properties (independently chosen molecular weight and radius of gyration) in a pure polymer-water system, eliminating the use of monomers, cross-linking agents, or other auxiliary substances.

Study of the effect of high dose rate on tissue equivalent proportional counter microdosimetric measurements in mixed photon and neutron fields

Abstract This study describes the measurement of lineal energy spectra carried out with a 5.1 cm (2 in.) diameter spherical tissue equivalent proportional counter (TEPC) simulating 2 μm tissue equivalent (TE) site diameter in low energy mixed photon–neutron fields with varying dose rates generated by employing the McMaster University 1.25 MV double stage Tandetron accelerator. The 7 Li (p, n) 7 Be reaction was employed to generate a variety of mixed fields of photons and low energy neutrons using proton beam energy ranging 1.89–2.56 MeV. The dose rate at a given beam energy was varied by changing the beam current. Dose rates that resulted in dead times as high as 75% were employed to study the effect of dose rate on quality, microdosimetric averages ( y¯ F and y¯ D ), absorbed dose and dose equivalent. We have observed that high dose rates due to both photons and neutrons in a mixed field of radiation result in pile up of pulses and distort the lineal energy spectrum measured under these conditions. The pile up effect and hence the distortion in the lineal energy spectrum becomes prominent with dose rates, which result in dead times larger than 25% for the high linear energy transfer (LET) radiation component. Intense neutron fields, which may amount to 75% dead time, could result in a 50% or even larger increase in the values of the microsdosimetric averages and the neutron quality factor. This study demonstrates moderate dose rates that do not result in dead times of more than 20–25% due to either of the component radiation or due to both components of mixed field radiation generate results that are acceptable for radiation monitoring.

Flow cytometric scoring of micronucleated reticulocytes as a possible high‐throughput radiation biodosimeter

Micronucleated reticulocyte (MN-RET) scoring by flow cytometry (FCM) has been used in assessment of the clastogenic effects of chemicals. However, its dose-response to acute whole body irradiation (WBI) at moderate dose rates remains to be established. We show that FCM scoring of MN-RET in peripheral blood from male ICR mice exposed to WBI X-ray doses of 0.5-5 Gy at a dose rate of 0.488 Gy/min exhibits a linear dose-response relationship 24, 48, and 72 hr following WBI. Parallel microscopic counting of micronucleated polychromatic erythrocytes (MN-PCE) in bone marrow smears from the same animals showed similar linear dose-response patterns at the same time points. Indeed, MN-RET and MN-PCE were highly correlated at all doses and time points. In view of the speed and accuracy of this method, in addition to the small blood sample size needed for the assay, the flow cytometric protocol for MN-RET scoring may provide a minimally-invasive, high throughput radiation biodosimeter.

A high energy barrier to charge recombination in ionized water vapor

A quantitative kinetic theory has been developed to explain the results of experimental observation of the abnormally intense clustering of water molecules in the vapor phase in an ionizing radiation field at a moderate dose rate. The recombination is impeded because of the hydration of ion pairs and the formation of an abnormally high energy barrier (∼100 k B T) in molecular clusters. The buildup of the clusters of water molecules stabilized in the electric field of ion pairs results in a dramatic enhancement of the effect of ionizing radiation on the electric properties of the vapor. The values of the coefficients to the rate equation of ionization-recombination equilibrium were calculated on the molecular level by computer simulation of the hydration of the H3O+(H2O) n OH− ion pair using the detailed model of intermolecular interactions.

Ageing of EUROBITUM bituminised radioactive waste: An ATR-FTIR spectroscopy study

The extent of the physico-chemical processes of concern in the study of the acceptability of Eurobitum bituminised radioactive waste for underground disposal (water uptake by hygroscopic NaNO 3 – swelling – pressure build-up – NaNO 3 leaching) will depend on the degree of ageing of the bituminous matrix. In the work reported here, the ageing behaviour was studied by comparing the characteristics of 25 years old radioactive Eurobitum with those of 25 years old non-radioactive Eurobitum samples that were heated or gamma-irradiated in the presence or absence of oxygen. Chemical changes in the bitumen structure were followed in the mid-infrared region with Attenuated Total Reflectance Fourier Transform InfraRed Spectroscopy (ATR-FTIR) by measuring the evolution of the band heights at 1700 cm −1 (C O functional groups) and 1600 cm −1 (C C double bonds). Needle penetration depths and ring and ball softening points were determined for some samples. Oxidation of bitumen in the presence of oxygen results in a distinct increase of both the number of C O and C C functionalities, with a positive linear relationship existing between the two groups. The production of C O functional groups seems to promote the generation of C C double bonds. Heating at 130 °C is much more efficient than gamma irradiation at low to moderate dose rates (20–140 Gy/h) to oxidise the bitumen. As the oxygen concentration decreases, for instance by diffusion limitation deeper inside the bitumen, the number of C O and C C functionalities formed per unit of time decreases. A similar behaviour was observed for 25 years old radioactive Eurobitum. In absence of oxygen, gamma irradiation still results in a small increase of the number of C O functional groups, probably by oxygen still adsorbed on the bitumen, and in a relatively higher amount of C C double bonds. The surface layer (<5 cm) of 25 years old radioactive Eurobitum was heavily oxidised. The material had become very hard and brittle, and was full of small fissures. Due to these fissures, radio-oxidation processes took also place deeper inside the waste. The consequences of these observations for the long-term behaviour of Eurobitum in underground disposal conditions are discussed.

Effect of maleic acid content on the thermal stability, swelling behaviour and network structure of gelatin-based hydrogels prepared by gamma irradiation

The highly swelling Poly (acrylamide/maleic acid/gelatin) P(AAm/MA/G) hydrogels were prepared by gamma-irradiation at low dose rate (0.94 kGy/h) and moderate dose rate (3.84 kGy/h). The hydrogels were confirmed by FTIR. The effect of copolymer composition, dose and dose rate on the swelling behaviour was discussed. Increasing of MA content and G in the initial mixture leads to an increase in the amount of MA and G in the gel system and decrease in the gelation %. The swelling behaviours of the hydrogel prepared at moderate dose rate increased with increasing MA mole content in the gel system but, there is no systematic dependence of swelling on MA content was observed for the hydrogels obtained at low dose rate. Pore structure of the hydrogels was monitored by using scanning electron microscopy. Thermogravimetric analysis (TGA) and the rate of the thermal decomposition of P(AAm/MA/G) hydrogels has been evaluated to give a better understanding of the thermal stability of polymers, The X-ray data of P(AAm/MA/G) hydrogels was discussed to investigate some features namely the degree of ordering and crystallite size.

Total ionizing dose effects in shallow trench isolation oxides

The peaked evolution of leakage current with total ionizing dose observed in transistors in 130 nm generation technologies is studied with field oxide field effect transistors (FOXFETs) that use the shallow trench isolation as gate oxide. The overall radiation response of these structures is determined by the balance between positive charge trapped in the bulk of the oxide and negative charge in defect centers at its interface with the silicon substrate. That these are mostly interface traps and not border traps is demonstrated through dynamic transconductance and variable-frequency charge-pumping measurements. These interface traps, whose formation is only marginally sensitive to the bias polarity across the oxide, have been observed to anneal at temperatures as low as 80 °C. At moderate or low dose rate, the buildup of interface traps more than offsets the increase in field oxide leakage due to oxide-trap charge. Consequences of these observations for circuit reliability are discussed.

EPR and UV investigation of sucrose irradiated with nitrogen ions and gamma-rays

Sucrose irradiated with N-ions and gamma-rays is investigated by EPR and UV spectroscopy. Irradiation doses are in the range of 20–380 Gy and linear energy transfer (LET) for N-ions of 90, 125 and 160 keV μ m - 1 . All EPR spectra recorded in irradiated solid samples are identical, suggesting that generated free radicals are not sensitive to the radiation quality. The EPR response of free radicals linearly depends on the absorbed dose but when generated by N-ions it is always lower than that obtained by irradiation with the same absorbed dose from gamma-rays. Water solutions of irradiated sucrose exhibit UV absorption at 267 nm due to the product of free radicals recombination, which spectrum remains independent on the radiation quality. The intensity of this band however depends on the absorbed dose and for equal doses it is higher for samples irradiated with N-ions than with gamma-rays. For different high LET-radiations with N-ions and low-LET radiation from gamma rays is found an excellent linearity between the EPR signal intensity and the UV absorbance of the obtained water solution. The relation between EPR and UV response of N-ions irradiated samples is reciprocal as well as between them and gamma-irradiated samples suggesting different impact of the high-energy photons and heavy particles on the solid state. For low LET photon radiation with moderate dose rate the probability for a successful hitting of two neighboring molecules is low. Therefore, only a small part of low LET radiation-induced free radicals may be expected to recombine giving an UV detectable product. In opposite, because of the dense ionizations and heaviness of N-ions almost all molecules in the core of the track are ionized yielding mainly products of the recombined free radicals. In the outer part of the track delta particles, which are more like low LET radiation electrons, stands for ionizations and produces a small number of free radicals situated far from each other. Therefore, we can expect higher EPR response of sugar irradiated with a certain dose of gamma-rays than of heavy particles. Just the opposite behavior should be expected for the UV absorption, which should be higher in the irradiation with heavy particles than with gamma-rays. The reported observations suggest that a sucrose/UV/EPR dosimetric system seems to be very promising for dose determinations from both gamma and heavy particle radiation and indicate a method for simultaneous determination of absorbed dose and LET. It also seems to be a new way for calibration of EPR dosimeters irradiated with N-ions via UV spectrometry.

Photosynthetic performance, oxidative damage and antioxidants in Cylindrotheca closterium in response to high irradiance, UVB radiation and salinity

Cylindrotheca closterium is a common marine diatom living in intertidal environments where it can be present both in the water column and on sediments, depending on the tidal regime. In the present work this diatom was employed to investigate the responses to desiccation and to increase in PAR and UVB intensity, as occurs during emersion. Under these circumstances, the production of active oxygen species (AOS) may be enhanced resulting in an oxidative stress. Stress responses in this species were measured by exposing it to normal (30) and double salinity (60), supplying light of low or high intensity for 12 h, in the latter case either without or with moderate dose rates of UVB. Pulse amplitude modulated fluorometry was used to measure Chl a autofluorescence (F0), an index of photosynthetic efficiency of PSII (Fv/Fm) and the relative electron transfer rate (rETR). The oxidative stress was evaluated by analysing GSH pools and SOD activity. It was observed that at double salinity and under low light, intracellular pools of reduced glutathione (GSH) were higher than under the two conditions of high light without and with UVB at both salinities. The antioxidative defence activity of superoxide dismutase (SOD) was far higher under hypersaline conditions. The oxidative damage was evaluated as protein and lipid damage. The results showed that it expressed itself mainly through protein peroxidation: at normal salinity relative protein carbonyl content was (a) twice as high as in cells grown at double salinity, and (b) three times as high under UVB. Total unsaturated lipid contents doubled under hypersalinity conditions. The lipid peroxidation marker malondialdehyde showed the strongest response to low light and UVB at salinity value of 60. Lipid peroxide content was significantly higher at salinity of 60 compared to normal salinity and was the highest under low light and high light with UVB. The simulated emersion condition of the diatom seems to lead to the establishment of a balance between damage and repair, expressed mainly as (a) oxidative protein damage at normal salinity, in particular due to UV radiation, (b) sufficient protection by SOD activity mainly under hypersaline conditions.

Development of an Improved Dose Reconstruction System for the Techa River Population Affected by the Operation of the Mayak Production Association

The Techa River Dosimetry System (TRDS) has been developed to provide estimates of dose received by approximately 30,000 members of the Extended Techa River Cohort (ETRC). Members of the ETRC were exposed beginning in 1949 to significant levels of external and internal (mainly from (90)Sr) dose but at low to moderate dose rates. Members of this cohort are being studied in an effort to test the hypothesis that exposure at low to moderate dose rates has the same ability to produce stochastic health effects as exposure at high dose rates. The current version of the TRDS is known as TRDS-2000 and is the subject of this paper. The estimated doses from (90)Sr are supported strongly by approximately 30,000 measurements made with a tooth beta-particle counter, measurements of bones collected at autopsy, and approximately 38,000 measurements made with a special whole-body counter that detects the bremsstrahlung from (90)Y. The median doses to the red bone marrow and the bone surface are 0.21 and 0.37 Gy, respectively. The maximum doses to the red bone marrow and bone surface are 2.0 and 5.2 Gy, respectively. Distributions of dose to other organs are provided and are lower than the values given above. Directions for future work are discussed.

Moderate dose rate ionizing radiation increases longevity?

Moderate dose rate ionizing radiation increases longevity?

Low dose radiation risk: UKRC 2004 debate

EditorialLow dose radiation risk: UKRC 2004 debateP DendyP DendySearch for more papers by this authorPublished Online:28 Jan 2014https://doi.org/10.1259/bjr/16783587SectionsPDF/EPUBFull Text ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail About"Low dose radiation risk: UKRC 2004 debate." The British Journal of Radiology, 78(925), pp. 1–2 References 1 Ionising Radiation (Medical Exposure) Regulations 2000 (Statutory Instrument 2000 No. 1059). London, UK: HMSO, 2000. Google Scholar2 Institute of Physics and Engineering in Medicine. Medical and dental guidance notes. A good practice guide to implementing ionising radiations legislation in the clinical environment. York, UK: IPEM, 2002. Google Scholar3 Dendy PP, Dixon B. Effects of human exposure to ionising radiation and risk estimates. In: Medical Imaging and Radiation Protection for Medical Students and Clinical Staff. Martin CJ, Dendy PP, Corbett RH, editors. London: British Institute of Radiology, 2003:103. Google Scholar4 Feinendegen LE. Evidence for beneficial low level radiation effects and radiation hormesis. Br J Radiol 2005;78:3–7. Link ISI, Google Scholar5 Chadwick KH, Leenhouts HP. Radiation risk is linear with dose at low doses. Br J Radiol 2005;78:8–10. Link ISI, Google Scholar6 Cameron JR. Moderate dose rate ionizing radiation increases longevity. Br J Radiol 2005;78:11–13. Link ISI, Google Scholar7 Martin CJ. The LNT model provides the best approach for practical implementation of radiation protection. Br J Radiol 2005;78:14–16. Link ISI, Google Scholar Next article FiguresReferencesRelatedDetailsCited byTowards Laser Driven Hadron Cancer Radiotherapy: A Review of Progress19 September 2014 | Applied Sciences, Vol. 4, No. 3Cell Cycle Regulators Guide Mitochondrial Activity in Radiation-Induced Adaptive ResponseAntioxidants & Redox Signaling, Vol. 20, No. 9Accuracy of Intraoperative Fluoroscopy with and without Laser Guidance in Foot and Ankle Surgery1 May 2012 | Foot & Ankle International, Vol. 33, No. 5Laser Radiation Pressure Accelerator for Quasi-Monoenergetic Proton Generation and Its Medical Implications20 June 2012Laser-driven particle and photon beams and some applications30 April 2010 | New Journal of Physics, Vol. 12, No. 4Interventional radiology20 December 2012Revised fundamental recommendations on radiological protectionNuclear Medicine Communications, Vol. 29, No. 4Laser-driven proton oncology — a unique new cancer therapy?K W D Ledingham, W Galster and R Sauerbrey28 January 2014 | The British Journal of Radiology, Vol. 80, No. 959BJR review of the year – 20065 March 2014 | The British Journal of Radiology, Vol. 80, No. 951Effective radiation doses in CT colonography: results of an inventory among research institutions18 January 2006 | European Radiology, Vol. 16, No. 5Ionizing Radiation, Biological Effects of14 April 2006BJR Review of the Year – 20055 March 2014 | The British Journal of Radiology, Vol. 79, No. 939LungentumorenDer Radiologe, Vol. 46, No. 218 F-FDG Uptake on PET/CT in Transposed OvariesAmerican Journal of Roentgenology, Vol. 186, No. 1 Volume 78, Issue 925January 2005Pages: 1-90 © The British Institute of Radiology History Published onlineJanuary 28,2014 Metrics Download PDF

Development of a low-energy monoenergetic neutron source for applications in low-dose radiobiological and radiochemical research

The McMaster University 3 MV KN Van de Graff accelerator facility primarily dedicated to in vivo neutron activation measurements has been used to produce moderate dose rates of monoenergetic fast neutrons of energy ranging from 150 to 600 keV with a small energy spread of about 25 keV (1 σ width of Gaussian) by bombarding thin lithium targets with 2.00–2.40 MeV protons. The calculated dose rate of the monoenergetic neutrons produced using thin lithium targets as functions of beam energy, target thickness, lab angle relative to beam direction, and the solid angle subtended by the sample with the target has also been reported.

Changing of network characteristics of acrylamide/maleic acid hydrogels by alteration of irradiation dose rate

Poly(acrylamide/maleic acid) P(AAm/MA) hydrogels were prepared by irradiating the ternary mixtures of AAm/MA and water by gamma rays at ambient temperature at very low (0.18 kGy/h), and moderate dose rate (3.0 kGy/h). The equilibrium degree of swelling (EDS) of hydrogels prepared at 3.0 kGy/h dose rate increased from 520% to 3900% with increasing MA mole content in the gel system from 0% to 5.2%. On the other hand, no systematic dependence of swelling on MA content was observed for hydrogels obtained at low dose rate irradiation due to formation of inhomogeneous network structure and large pores in the gel. Pore structure of hydrogels was monitored by using scanning electron microscope. Systematic swelling of P(AAm/MA) hydrogels prepared at moderate dose rates can be explained with homogeneous pore size distribution of network.

Effects of low-dose neutrons applied at reduced dose rate on human melanoma cells.

Human melanoma cells that are resistant to gamma rays were irradiated with 14 MeV neutrons given at low doses ranging from 5 cGy to 1.12 Gy at a very low dose rate of 0.8 mGy min(-1) or a moderate dose rate of 40 mGy min(-1). The biological effects of neutrons were studied by two different methods: a cell survival assay after a 14-day incubation and an analysis of chromosomal aberrations in metaphases collected 20 h after irradiation. Unusual features of the survival curve at very low dose rate were a marked increase in cell killing at 5 cGy followed by a plateau for survival from 10 to 32.5 cGy. The levels of induced chromosomal aberrations showed a similar increase for both dose rates at 7.5 cGy and the existence of a plateau at the very low dose rate from 15 to 30 cGy. The existence of a plateau suggests that a repair process after low-dose neutrons might be induced after a threshold dose of 5-7.5 cGy which compensates for induced damage from doses as high as 32.5 cGy. These findings may be of interest for understanding the relative biological effectiveness of neutrons and the effects of environmental low-dose irradiation.