[Application Status and Development Trends of Medical Proton and Heavy Ion Accelerators]

Cancer therapy with accelerated proton or heavy ion beam is the most advanced radiotherapy technology, which is recognized by the international community at present. It is of great practical significance to study the medical proton and heavy ion accelerators and the radiotherapy technology, in order to promote the development of the advanced medical radiotherapy equipments and improve the quality of life of cancer patients in China. After a brief overview of cancer therapy with proton and heavy ion beam, this paper summarized and analyzed the application status of medical proton accelerators and medical heavy ion accelerators at home and abroad, and finally put forward the future development trends of medical proton and heavy ion accelerators and the radiotherapy technology, it can provide a reference for the progress and development strategies of the advanced radiotherapy equipments in China.

Arabidopsis CNGC Family Members Contribute to Heavy Metal Ion Uptake in Plants

Heavy metal ions, including toxic concentrations of essential ions, negatively affect diverse metabolic and cellular processes. Heavy metal ions are known to enter cells in a non-selective manner; however, few studies have examined the regulation of heavy metal ion transport. Plant cyclic nucleotide-gated channels (CNGCs), a type of Ca2+-permeable-channel, have been suggested to be involved in the uptake of both essential and toxic cations. To determine the candidates responsible for heavy metal ion transport, a series of Arabidopsis CNGC mutants were examined for their response to Pb2+ and Cd2+ ions. The primary focus was on root growth and the analysis of the concentration of heavy metals in plants. Results, based on the analysis of primary root length, indicated that AtCNGC1, AtCNGC10, AtCNGC13 and AtCNGC19 play roles in Pb2+ toxicity, while AtCNGC11, AtCNGC13, AtCNGC16 and AtCNGC20 function in Cd2+ toxicity in Arabidopsis. Ion content analysis verified that the mutations of AtCNGC1 and AtCNGC13 resulted in reduced Pb2+ accumulation, while the mutations of AtCNGC11, AtCNGC15 and AtCNGC19 resulted in less Pb2+ and Cd2+ accumulation in plants. These findings provide functional evidence which support the roles of these AtCNGCs in the uptake and transport of Pb2+ or Cd2+ ion in plants.

Potential lethal damage repair in glioblastoma cells irradiated with ion beams of various types and levels of linear energy transfer

Glioblastoma (GBM), a Grade IV brain tumour, is a well-known radioresistant cancer. To investigate one of the causes of radioresistance, we studied the capacity for potential lethal damage repair (PLDR) of three altered strains of GBM: T98G, U87 and LN18, irradiated with various ions and various levels of linear energy transfer (LET). The GBM cells were exposed to 12C and 28Si ion beams with LETs of 55, 100 and 200 keV/μm, and with X-ray beams of 1.7 keV/μm. Mono-energetic 12C ions and 28Si ions were generated by the Heavy Ion Medical Accelerator at the National Institute of Radiological Science, Chiba, Japan. Clonogenic assays were used to determine cell inactivation. The ability of the cells to repair potential lethal damage was demonstrated by allowing one identical set of irradiated cells to repair for 24 h before subplating. The results show there is definite PLDR with X-rays, some evidence of PLDR at 55 keV/μm, and minimal PLDR at 100 keV/μm. There is no observable PLDR at 200 keV/μm. This is the first study, to the authors' knowledge, demonstrating the capability of GBM cells to repair potential lethal damage following charged ion irradiations. It is concluded that a GBM's PLDR is dependent on LET, dose and GBM strain; and the more radioresistant the cell strain, the greater the PLDR.

Clustered DNA double-strand break formation and the repair pathway following heavy-ion irradiation

Photons, such as X- or γ-rays, induce DNA damage (distributed throughout the nucleus) as a result of low-density energy deposition. In contrast, particle irradiation with high linear energy transfer (LET) deposits high-density energy along the particle track. High-LET heavy-ion irradiation generates a greater number and more complex critical chromosomal aberrations, such as dicentrics and translocations, compared with X-ray or γ irradiation. In addition, the formation of >1000 bp deletions, which is rarely observed after X-ray irradiation, has been identified following high-LET heavy-ion irradiation. Previously, these chromosomal aberrations have been thought to be the result of misrepair of complex DNA lesions, defined as DNA damage through DNA double-strand breaks (DSBs) and single-strand breaks as well as base damage within 1-2 helical turns (<3-4 nm). However, because the scale of complex DNA lesions is less than a few nanometers, the large-scale chromosomal aberrations at a micrometer level cannot be simply explained by complex DNA lesions. Recently, we have demonstrated the existence of clustered DSBs along the particle track through the use of super-resolution microscopy. Furthermore, we have visualized high-level and frequent formation of DSBs at the chromosomal boundary following high-LET heavy-ion irradiation. In this review, we summarize the latest findings regarding the hallmarks of DNA damage structure and the repair pathway following heavy-ion irradiation. Furthermore, we discuss the mechanism through which high-LET heavy-ion irradiation may induce dicentrics, translocations and large deletions.

Role of carbon ion beams irradiation in mitigating cold stress in Arabidopsis thaliana

Carbon ion beams irradiation as an important type of ionizing radiation is one of the major approaches used to create mutants in plants. This study investigated the role of carbon ion beams irradiation in mitigating cold stress in Arabidopsis thaliana seedlings. The results showed that 50-Gy carbon ion beam irradiation appeared stimulatory effects on root length and fresh weight in Arabidopsis seedlings under cold stress. In comparison with control, the content of hydrogen peroxide, the production rate of superoxide anion radical, hydroxyl radical generation activity, and malondialdehyde content were obviously decreased in 50-Gy carbon ion beam irradiated seedlings in response to cold stress. Moreover, irradiated 50-Gy carbon ion beam in Arabidopsis seedlings were significantly triggered the efficiency of antioxidant under cold stress. Furthermore, we investigated the expression of cold-related genes in irradiated and non-irradiated samples. Carbon ion beams irradiation up-regulated the expression levels of C-REPEAT BINDING FACTORS (CBFs), INDUCER OF CBF EXPRESSION 1 (ICE1), ICE2, CALMODULIN-BINDING TRANSCRIPTION ACTIVATOR 3 (CAMTA3) and cold-regulated COR genes, in response to cold stress. This study suggests that low-dose carbon ion beams irradiation can modulate the physiological responses and up-regulate cold signaling genes in mitigating cold stress in the growth of Arabidopsis seedlings.

Analysis of DNA methylation alterations in rice seeds induced by different doses of carbon-ion radiation

To investigate the mechanism underlying differences in biological effects induced by low- versus high-dose heavy-ion radiation (HIR) in rice plants, two-dimensional gel electrophoresis (2-DE) coupled with methylation-sensitive amplification polymorphism (MSAP) analysis were used to check the expression changes in rice leaf proteome profiles and the changes in DNA methylation after exposure of seeds to ground-based carbon-ion radiation at various cumulative doses (0, 0.01, 0.02, 0.1, 0.2, 1, 2, 5 or 20 Gy; 12C6+; energy, 165 MeV/u; mean linear energy transfer, 30 KeV/μm). In this study, principal component analysis (PCA) and gene ontology (GO) functional analysis of differentially expressed proteins of rice at tillering stage showed that proteins expressed in rice samples exposed to 0.01, 0.02, 0.1, 0.2 or 1 Gy differed from those exposed to 2, 5 or 20 Gy. Correspondingly, the proportion of hypermethylation was higher than that of hypomethylation at CG sites following low-dose HIR (LDR; 0.01, 0.2 or 1 Gy), whereas this was reversed at high-dose HIR (HDR; 2, 5 or 20 Gy). The hypomethylation changes tended to occur at CHG sites with both low- and high-dose HIR. Furthermore, sequencing of MSAP variant bands indicated that the plants might activate more metabolic processes and biosynthetic pathways on exposure to LDR, but activate stress resistance on exposure to HDR. This study showed that radiation induced different biological effects with low- and high-dose HIR, and that this may have been caused by different patterns of hyper- and hypomethylation at the CG sites.

High LET radiation shows no major cellular and functional effects on primary cardiomyocytes in vitro

It is well known that ionizing radiation causes adverse effects on various mammalian tissues. However, there is little information on the biological effects of heavy ion radiation on the heart. In order to fill this gap, we systematically examined DNA-damage induction and repair, as well as proliferation and apoptosis in avian cardiomyocyte cultures irradiated with heavy ions such as titanium and iron, relevant for manned space-flight, and carbon ions, as used for radiotherapy. Further, and to our knowledge for the first time, we analyzed the effect of heavy ion radiation on the electrophysiology of primary cardiomyocytes derived from chicken embryos using the non-invasive microelectrode array (MEA) technology. As electrophysiological endpoints beat rate and field action potential duration were analyzed. The cultures clearly exhibited the capacity to repair induced DNA damage almost completely within 24 h, even at doses of 7 Gy, and almost completely recovered from radiation-induced changes in proliferative behavior. Interestingly, no significant effects on apoptosis could be detected. Especially the functionality of primary cardiac cells exhibited a surprisingly high robustness against heavy ion radiation, even at doses of up to 7 Gy. In contrast to our previous study with X-rays the beat rate remained more or less unaffected after heavy ion radiation, independently of beam quality. The only change we could observe was an increase of the field action potential duration of up to 30% after titanium irradiation, diminishing within the following three days. This potentially pathological observation may be an indication that heavy ion irradiation at high doses could bear a long-term risk for cardiovascular disease induction.

Different mutational function of low- and high-linear energy transfer heavy-ion irradiation demonstrated by whole-genome resequencing of Arabidopsis mutants

Heavy-ion irradiation is a powerful mutagen that possesses high linear energy transfer (LET). Several studies have indicated that the value of LET affects DNA lesion formation in several ways, including the efficiency and the density of double-stranded break induction along the particle path. We assumed that the mutation type can be altered by selecting an appropriate LET value. Here, we quantitatively demonstrate differences in the mutation type induced by irradiation with two representative ions, Ar ions (LET: 290 keV μm^-1 ) and C ions (LET: 30.0 keV μm^-1 ), by whole-genome resequencing of the Arabidopsis mutants produced by these irradiations. Ar ions caused chromosomal rearrangements or large deletions (≥100 bp) more frequently than C ions, with 10.2 and 2.3 per mutant genome under Ar- and C-ion irradiation, respectively. Conversely, C ions induced more single-base substitutions and small indels (<100 bp) than Ar ions, with 28.1 and 56.9 per mutant genome under Ar- and C-ion irradiation, respectively. Moreover, the rearrangements induced by Ar-ion irradiation were more complex than those induced by C-ion irradiation, and tended to accompany single base substitutions or small indels located close by. In conjunction with the detection of causative genes through high-throughput sequencing, selective irradiation by beams with different effects will be a powerful tool for forward genetics as well as studies on chromosomal rearrangements.

Region-specific irradiation system with heavy-ion microbeam for active individuals of Caenorhabditis elegans

Radiation may affect essential functions and behaviors such as locomotion, feeding, learning and memory. Although whole-body irradiation has been shown to reduce motility in the nematode Caenorhabditis elegans, the detailed mechanism responsible for this effect remains unknown. Targeted irradiation of the nerve ring responsible for sensory integration and information processing would allow us to determine whether the reduction of motility following whole-body irradiation reflects effects on the central nervous system or on the muscle cells themselves. We therefore addressed this issue using a collimating microbeam system. However, radiation targeting requires the animal to be immobilized, and previous studies have anesthetized animals to prevent their movement, thus making it impossible to assess their locomotion immediately after irradiation. We developed a method in which the animal was enclosed in a straight, microfluidic channel in a polydimethylsiloxane chip to inhibit free motion during irradiation, thus allowing locomotion to be observed immediately after irradiation. The head region (including the central nervous system), mid region around the intestine and uterus, and tail region were targeted independently. Each region was irradiated with 12 000 carbon ions (12C; 18.3 MeV/u; linear energy transfer = 106.4 keV/μm), corresponding to 500 Gy at a φ20 μm region. Motility was significantly decreased by whole-body irradiation, but not by irradiation of any of the individual regions, including the central nervous system. This suggests that radiation inhibits locomotion by a whole-body mechanism, potentially involving motoneurons and/or body-wall muscle cells, rather than affecting motor control via the central nervous system and the stimulation response.

Estimation of whole-body radiation exposure from brachytherapy for oral cancer using a Monte Carlo simulation

Early stage oral cancer can be cured with oral brachytherapy, but whole-body radiation exposure status has not been previously studied. Recently, the International Commission on Radiological Protection Committee (ICRP) recommended the use of ICRP phantoms to estimate radiation exposure from external and internal radiation sources. In this study, we used a Monte Carlo simulation with ICRP phantoms to estimate whole-body exposure from oral brachytherapy. We used a Particle and Heavy Ion Transport code System (PHITS) to model oral brachytherapy with 192Ir hairpins and 198Au grains and to perform a Monte Carlo simulation on the ICRP adult reference computational phantoms. To confirm the simulations, we also computed local dose distributions from these small sources, and compared them with the results from Oncentra manual Low Dose Rate Treatment Planning (mLDR) software which is used in day-to-day clinical practice. We successfully obtained data on absorbed dose for each organ in males and females. Sex-averaged equivalent doses were 0.547 and 0.710 Sv with 192Ir hairpins and 198Au grains, respectively. Simulation with PHITS was reliable when compared with an alternative computational technique using mLDR software. We concluded that the absorbed dose for each organ and whole-body exposure from oral brachytherapy can be estimated with Monte Carlo simulation using PHITS on ICRP reference phantoms. Effective doses for patients with oral cancer were obtained.

Changes in transcript levels of starch hydrolysis genes and raising citric acid production via carbon ion irradiation mutagenesis of Aspergillus niger

The filamentous ascomycete Aspergillus niger is well known for its ability to accumulate citric acid for the hydrolysis of starchy materials. To improve citric acid productivity, heavy ion beam mutagenesis was utilized to produce mutant A.niger strains with enhanced production of citric acid in this work. It was demonstrated that a mutant HW2 with high concentration of citric acid was isolated after carbon ion irradiation with the energy of 80Mev/μ, which was obvious increase higher than the original strain from liquefied corn starch as a feedstock. More importantly, with the evidence from the expression profiles of key genes and enzyme activity involved in the starch hydrolysis process between original strain and various phenotype mutants, our results confirmed that different transcript levels of key genes involving in starch hydrolysis process between original strain and mutants could be a significant contributor to different citric acid concentration in A.niger, such as, amyR and glaA, which therefore opened a new avenue for constructing genetically engineered A.niger mutants for high-yield citric acid accumulation in the future. As such, this work demonstrated that heavy ion beam mutagenesis presented an efficient alternative strategy to be developed to generate various phenotype microbe species mutants for functional genes research.

Apoptosis and injuries of heavy ion beam and x-ray radiation on malignant melanoma cell

This study aims to investigate the influence of high linear energy transfer (LET) heavy ion (12C6+) and low LET X-ray radiation on apoptosis and related proteins of malignant melanoma on tumor-bearing mice under the same physical dosage. C57BL/6 J mice were burdened by tumors and randomized into three groups. These mice received heavy ion (12C6+) and X-ray radiation under the same physical dosage, respectively; their weight and tumor volumes were measured every three days post-radiation. After 30 days, these mice were sacrificed. Then, median survival time was calculated and tumors on mice were proliferated. In addition, immunohistochemistry was carried out for apoptosis-related proteins to reflect the expression level. After tumor-bearing mice were radiated to heavy ion, median survival time improved and tumor volume significantly decreased in conjunction with the upregulated expression of pro-apoptosis factors, Bax and cytochrome C, and the downregulated expression of apoptosis-profilin (Bcl-2, Survivin) and proliferation-related proteins (proliferating cell nuclear antigen). The results indicated that radiation can promote the apoptosis of malignant melanoma cells and inhibit their proliferation. This case was more suitable for heavy ion (12C6+). High LET heavy ion (12C6+) radiation could significantly improve the killing ability for malignant melanoma cells by inducing apoptosis in tumor cells and inhibiting their proliferation. These results demonstrated that heavy ion (12C6+) presented special advantages in terms of treating malignant melanoma. Impact statement Malignant melanoma is a malignant skin tumor derived from melanin cells, which has a high malignant degree and high fatality rate. In this study, proliferating cell nuclear antigen (PCNA) can induce the apoptosis of malignant melanoma cells and inhibit its proliferation, and its induction effect on apoptosis is significantly higher than low LET X-ray; hence, it is expected to overcome its lower sensitivity to radiation. This study can provide theoretical basis for clinical trials, in which malignant melanoma is treated by heavy ion (12C6+), in order to accurately determine the clinical efficacy of heavy ion therapy. Clinical applications has revealed that local tumor control rate is high when heavy ion is used to treat malignant melanoma, indicating that heavy ion is an important direction in treating melanoma in the future.

Track structure model of microscopic energy deposition by protons and heavy ions in segments of neuronal cell dendrites represented by cylinders or spheres

Changes to cognition, including memory, following radiation exposure are a concern for cosmic ray exposures to astronauts and in Hadron therapy with proton and heavy ion beams. The purpose of the present work is to develop computational methods to evaluate microscopic energy deposition (ED) in volumes representative of neuron cell structures, including segments of dendrites and spines, using a stochastic track structure model. A challenge for biophysical models of neuronal damage is the large sizes (> 100µm) and variability in volumes of possible dendritic segments and pre-synaptic elements (spines and filopodia). We consider cylindrical and spherical microscopic volumes of varying geometric parameters and aspect ratios from 0.5 to 5 irradiated by protons, and ³He and ¹²C particles at energies corresponding to a distance of 1cm to the Bragg peak, which represent particles of interest in Hadron therapy as well as space radiation exposure. We investigate the optimal axis length of dendritic segments to evaluate microscopic ED and hit probabilities along the dendritic branches at a given macroscopic dose. Because of large computation times to analyze ED in volumes of varying sizes, we developed an analytical method to find the mean primary dose in spheres that can guide numerical methods to find the primary dose distribution for cylinders. Considering cylindrical segments of varying aspect ratio at constant volume, we assess the chord length distribution, mean number of hits and ED profiles by primary particles and secondary electrons (δ-rays). For biophysical modeling applications, segments on dendritic branches are proposed to have equal diameters and axes lengths along the varying diameter of a dendritic branch.

Radioresistance of Adenine to Cosmic Rays

The presence of nucleobases in carbonaceous meteorites on Earth is an indication of the existence of this class of molecules in outer space. However, space is permeated by ionizing radiation, which can have damaging effects on these molecules. Adenine is a purine nucleobase that amalgamates important biomolecules such as DNA, RNA, and ATP. Adenine has a unique importance in biochemistry and therefore life. The aim of this work was to study the effects of cosmic ray analogues on solid adenine and estimate its survival when exposed to corpuscular radiation. Adenine films were irradiated at GANIL (Caen, France) and GSI (Darmstadt, Germany) by 820 MeV Kr³³⁺, 190 MeV Ca¹⁰⁺, 92 MeV Xe²³⁺, and 12 MeV C⁴⁺ ion beams at low temperature. The evolution of adenine molecules under heavy ion irradiation was studied by IR absorption spectroscopy as a function of projectile fluence. It was found that the adenine destruction cross section (σ_d) follows an electronic stopping power (S_e) power law under the form: CS_eⁿ; C is a constant, and the exponential n is a dimensionless quantity. Using the equation above to fit our results, we determined σ_d = 4 × 10^-17 S_e^1.17, with S_e in kiloelectronvolts per micrometer (keV μm^-1). New IR absorption bands arise under irradiation of adenine and can be attributed to HCN, CN^-, C₂H₄N₄, CH₃CN, and (CH₃)₃CNC. These findings may help to understand the stability and chemistry related to complex organic molecules in space. The half-life of solid adenine exposed to the simulated interstellar medium cosmic ray flux was estimated as (10 ± 8) × 10⁶ years. Key Words: Heavy ions-Infrared spectroscopy-Astrochemistry-Cosmic rays-Nucleobases-Adenine. Astrobiology 17, 298-308.

The Effects of HZE Particles, γ and X-ray Radiation on the Survival and Genetic Integrity of Halobacterium salinarum NRC-1, Halococcus hamelinensis, and Halococcus morrhuae

Three halophilic archaea, Halobacterium salinarum NRC-1, Halococcus hamelinensis, and Halococcus morrhuae, have been exposed to different regimes of simulated outer space ionizing radiation. Strains were exposed to high-energy heavy ion (HZE) particles, namely iron and argon ions, as well as to γ radiation (⁶⁰Co) and X-rays, and the survival and the genetic integrity of the 16S rRNA gene were evaluated. Exposure to 1 kGy of argon or iron ions at the Heavy Ion Medical Accelerator in Chiba (HIMAC) facility at the National Institute for Radiological Sciences (NIRS) in Japan did not lead to a detectable loss in viability; only after exposure to 2 kGy of iron ions a decline in survival was observed. Furthermore, a delay in growth was manifested following exposure to 2 kGy iron ions. DNA integrity of the 16S rRNA was not compromised up to 1 kGy, with the exception of Hcc. hamelinensis following exposure to argon particles. All three strains showed a high resistance toward X-rays (exposed at the DLR in Cologne, Germany), where Hcc. hamelinensis and Hcc. morrhuae displayed better survival compared to Hbt. salinarum NRC-1. In all three organisms the DNA damage increased in a dose-dependent manner. To determine a biological endpoint for survival following exposure to γ radiation, strains were exposed to up to 112 kGy at the Beta-Gamma-Service GmbH (BGS) in Germany. Although all strains were incubated for up to 4 months, only Hcc. hamelinensis and Hcc. morrhuae recovered from 6 kGy of γ radiation. In comparison, Hbt. salinarum NRC-1 did not recover. The 16S rRNA gene integrity stayed remarkably well preserved up to 48 kGy for both halococci. This research presents novel data on the survival and genetic stability of three halophilic archaea following exposure to simulated outer space radiation. Key Words: Halophilic archaea-Radiation-Survival. Astrobiology 17, 110-117.

Tolerance to X-rays and Heavy Ions (Fe, He) in the Tardigrade Richtersius coronifer and the Bdelloid Rotifer Mniobia russeola

The aim of this study was to analyze tolerance to heavy ions in desiccated animals of the eutardigrade Richtersius coronifer and the bdelloid rotifer Mniobia russeola within the STARLIFE project. Both species were exposed to iron (Fe) and helium (He) ions at the Heavy Ion Medical Accelerator in Chiba (HIMAC) in Chiba, Japan, and to X-rays at the German Aerospace Center (DLR) in Cologne, Germany. Results show no effect of Fe and He on viability up to 7 days post-rehydration in both R. coronifer and M. russeola, while X-rays tended to reduce viability in R. coronifer at the highest doses. Mean egg production rate tended to decline with higher doses in R. coronifer for all radiation types, but the pattern was not statistically confirmed. In M. russeola, there was no such tendency for a dose response in egg production rate. These results confirm the previously reported high tolerance to high linear energy transfer (LET) radiation in tardigrades and show for the first time that bdelloid rotifers are also very tolerant to high-LET radiation. These animal phyla represent the most desiccation- and radiation-tolerant animals on Earth and provide excellent eukaryotic models for astrobiological research. Key Words: Tardigrada-Rotifera-Radiation tolerance-Heavy ions-X-rays. Astrobiology 17, 163-167.

L Band EPR Tooth Dosimetry for Heavy Ion Irradiation

Electron Paramagnetic Resonance (EPR) tooth dosimetry is being developed as a device to rapidly assess large populations that were potentially exposed to radiation during a major radiation accident or terrorist event. While most exposures are likely to be due to fallout and therefore involve low linear energy transfer (LET) radiation, there is also a potential for exposures to high LET radiation, for which the effect on teeth has been less well characterized by EPR. Therefore, the aim of this paper is to acquire fundamental response curves for high LET radiation in tooth dosimetry using L band EPR. For this purpose, we exposed human teeth to high energy carbon ions using the heavy ion medical accelerator in Chiba at the National Institute of Radiological Sciences. The primary findings were that EPR signals for carbon ion irradiation were about one-tenth the amplitude of the response to the same dose of 150 kVp X-rays.

First Evidence on the Role of Heavy Ion Irradiation of Meteorites and Formamide in the Origin of Biomolecules

Formamide (NH2CHO) has been irradiated in condensed phase at 273 K by 11B-boron beams in the presence of powdered meteorites of the chondrite and stony-iron types. Relative to the controls (no radiation or no catalysis), a variegate panel of compounds was observed, including purine and pyrimidine nucleobases (uracil, cytosine, adenine, and guanine), nucleobase analogues, heterocycles, and carboxylic acids involved in metabolic pathways. The presence of amino imidazole carbonitrile (AICN), 4,6-diamino purine (4,6-DAP) and 2,4-diamino pyrimidine (2,4-DAPy) among the observed products suggests the occurrence of an unified mechanism based on the generation of radical cyanide species (•CN). These observations contribute to outline plausible prebiotic scenarios involving 11B-boron as energy source.

Neutron emission and dose distribution from natural carbon irradiated with a 12 MeV amu-1 12C5+ ion beam

Measured neutron energy distribution emitted from a thick stopping target of natural carbon at 0°, 30°, 60° and 90° from nuclear reactions caused by 12 MeV amu^-1 incident ¹²C⁵⁺ ions were converted to energy differential and total neutron absorbed dose as well as ambient dose equivalent H ^*(10) using the fluence-to-dose conversion coefficients provided by the ICRP. Theoretical estimates were obtained using the Monte Carlo nuclear reaction model code PACE and a few existing empirical formulations for comparison. Results from the PACE code showed an underestimation of the high-energy part of energy differential dose distributions at forward angles whereas the empirical formulation by Clapier and Zaidins (1983 Nucl. Instrum. Methods 217 489-94) approximated the energy integrated angular distribution of H ^*(10) satisfactorily. Using the measured data, the neutron doses received by some vital human organs were estimated for anterior-posterior exposure. The estimated energy-averaged quality factors were found to vary for different organs from about 7 to about 13. Emitted neutrons having energies above 20 MeV were found to contribute about 20% of the total dose at 0° while at 90° the contribution was reduced to about 2%.

Trace heavy metal ions promoted extracellular electron transfer and power generation by Shewanella in microbial fuel cells

Although microbial fuel cells (MFCs) is considered as one of the most promising technology for renewable energy harvesting, low power output still accounts one of the bottlenecks and limits its further development. In this work, it is found that Cu(2+) (0.1μgL(-1)-0.1mgL(-1)) or Cd(2+) (0.1μgL(-1)-1mgL(-1)) significantly improve the electricity generation in MFCs. The maximum power output achieved with trace level of Cu(2+) (∼6nM) or Cd(2+) (∼5nM) is 1.3 times and 1.6 times higher than that of the control, respectively. Further analysis verifies that addition of Cu(2+) or Cd(2+) effectively improves riboflavin production and bacteria attachment on the electrode, which enhances bacterial extracellular electron transfer (EET) in MFCs. These results unveil the mechanism for power output enhancement by Cu(2+) or Cd(2+) addition, and suggest that metal ion addition should be a promising strategy to enhance EET as well as power generation of MFCs.

Radiological properties of nanocomposite Fricke gel dosimeters for heavy ion beams

The radiological properties of nanocomposite Fricke gel (NC-FG) dosimeters prepared with different concentrations of nano-clay, perchloric acid and ferrous ions in deaerated conditions were investigated under carbon and argon ion beam irradiation covering a linear-energy-transfer (LET) range of 10 to 3000 eV/nm. We found that NC-FG exhibits radiological properties distinct from those of conventional Fricke gel. The radiation sensitivity of NC-FG is independent of the LET and is nearly constant even at very high LET (3000 eV/nm) values in the Bragg peak region of the argon ion beam. In addition, whereas conventional Fricke gel dosimeters only operate under acidic conditions, NC-FG dosimeters function under both acidic and neutral conditions. The radiation sensitivity decreases with decreasing nano-clay concentration in NC-FG, which indicates that the nano-clay plays a vital role in the radiation-induced oxidation of Fe(2.)

Both Complexity and Location of DNA Damage Contribute to Cellular Senescence Induced by Ionizing Radiation

Persistent DNA damage is considered as a main cause of cellular senescence induced by ionizing radiation. However, the molecular bases of the DNA damage and their contribution to cellular senescence are not completely clear. In this study, we found that both heavy ions and X-rays induced senescence in human uveal melanoma 92–1 cells. By measuring senescence associated-β-galactosidase and cell proliferation, we identified that heavy ions were more effective at inducing senescence than X-rays. We observed less efficient repair when DNA damage was induced by heavy ions compared with X-rays and most of the irreparable damage was complex of single strand breaks and double strand breaks, while DNA damage induced by X-rays was mostly repaired in 24 hours and the remained damage was preferentially associated with telomeric DNA. Our results suggest that DNA damage induced by heavy ion is often complex and difficult to repair, thus presents as persistent DNA damage and pushes the cell into senescence. In contrast, persistent DNA damage induced by X-rays is preferentially associated with telomeric DNA and the telomere-favored persistent DNA damage contributes to X-rays induced cellular senescence. These findings provide new insight into the understanding of high relative biological effectiveness of heavy ions relevant to cancer therapy and space radiation research.

A priming dose of protons alters the early cardiac cellular and molecular response to (56)Fe irradiation

PURPOSE

Recent evidence suggests that the heart may be injured by ionizing radiation at lower doses than was previously thought. This raises concerns about the cardiovascular risks from exposure to radiation during space travel. Since space travel is associated with exposure to both protons from solar particle events and heavy ions from galactic cosmic rays, we here examined the effects of a "priming" dose of protons on the cardiac cellular and molecular response to a "challenge" dose of (56)Fe in a mouse model.

METHODS

Male C57BL/6 mice at 10 weeks of age were exposed to sham-irradiation, 0.1 Gy of protons (150 MeV), 0.5 Gy of (56)Fe (600 MeV/n), or 0.1 Gy of protons 24 hours prior to 0.5 Gy of (56)Fe. Hearts were obtained at 7 days post-irradiation and western-blots were used to determine protein markers of cardiac remodeling, inflammatory infiltration, and cell death.

RESULTS

Exposure to (56)Fe caused an increase in expression of α-smooth muscle cell actin, collagen type III, the inflammatory cell markers mast cell tryptase, CD2 and CD68, the endothelial glycoprotein thrombomodulin, and cleaved caspase 3. Of all proteins investigated, protons at a dose of 0.1 Gy induced a small increase only in cleaved caspase 3 levels. On the other hand, exposure to protons 24 hours before (56)Fe prevented all of the responses to (56)Fe.

CONCLUSIONS

This study shows that a low dose of protons may prime the heart to respond differently to a subsequent challenge dose of heavy ions. Further investigation is required to identify responses at additional time points, consequences for cardiac function, threshold dose levels, and mechanisms by which a proton priming dose may alter the response to heavy ions.

Measurement of the stochastic radial dose distribution for a 30-MeV proton beam using a wall-less tissue-equivalent proportional counter

The frequency distribution of the lineal energy, y, of a 30-MeV proton beam was measured as a function of the radial distance from the beam path, and the dosed mean of y, y¯(D), was obtained to investigate the radial dependence of y¯(D). A wall-less tissue-equivalent proportional counter, in a cylindrical volume with simulated diameters of 0.36, 0.72 and 1.44 µm was used for the measurement of y distributions, yf(y). The measured values of yf(y) summed in the radial direction agreed fairly well with the corresponding data taken from the microdosimetric calculations using the PHITS code. The y¯(D) value of the 30-MeV proton beam presented its smallest value at r = 0.0 and gradually increased with radial distance, and the y¯(D) values of heavy ions such as iron showed rapid decrease with radial distance. This experimental result demonstrated that the stochastic deposited energy distribution of high-energy protons in the microscopic region is rather constant in the core as well as in the penumbra region of the track structure.

Combined exposure to protons and (56)Fe leads to overexpression of Il13 and reactivation of repetitive elements in the mouse lung

Interest in deep space exploration underlines the needs to investigate the effects of exposure to combined sources of space radiation. The lung is a target organ for radiation, and exposure to protons and heavy ions as radiation sources may lead to the development of degenerative disease and cancer. In this study, we evaluated the pro-fibrotic and epigenetic effects of exposure to protons (150 MeV/nucleon, 0.1 Gy) and heavy iron ions ((56)Fe, 600 MeV/nucleon, 0.5 Gy) alone or in combination (protons on Day 1 and (56)Fe on Day 2) in C57BL/6 male mice 4 weeks after irradiation. Exposure to (56)Fe, proton or in combination, did not result in histopathological changes in the murine lung. At the same time, combined exposure to protons and (56)Fe resulted in pronounced molecular alterations in comparison with either source of radiation alone. Specifically, we observed a substantial increase in the expression of cytokine Il13, loss of expression of DNA methyltransferase Dnmt1, and reactivation of LINE-1, SINE B1 retrotransposons, and major and minor satellites. Given the deleterious potential of the observed effects that may lead to development of chronic lung injury, pulmonary fibrosis, and cancer, future studies devoted to the investigation of the long-term effects of combined exposures to proton and heavy ions are clearly needed.