Comparison of organ dose and dose equivalent for human phantoms of CAM vs. MAX

For the evaluation of organ dose and dose equivalent of astronauts on space shuttle and the International Space Station (ISS) missions, the CAMERA models of CAM (Computerized Anatomical Male) and CAF (Computerized Anatomical Female) of human tissue shielding have been implemented and used in radiation transport model calculations at NASA. One of new human geometry models to meet the “reference person” of International Commission on Radiological Protection (ICRP) is based on detailed Voxel (volumetric and pixel) phantom models denoted for male and female as MAX (Male Adult voXel) and FAX (Female Adult voXel), respectively. We compared the CAM model predictions of organ doses to those of MAX model, since the MAX model represents the male adult body with much higher fidelity than the CAM model currently used at NASA. Directional body-shielding mass was evaluated for over 1500 target points of MAX for specified organs considered to be sensitive to the induction of stochastic effects. Radiation exposures to solar particle event (SPE), trapped protons, and galactic cosmic ray (GCR) were assessed at the specific sites in the MAX phantom by coupling space radiation transport models with the relevant body-shielding mass. The development of multiple-point body-shielding distributions at each organ made it possible to estimate the mean and variance of organ doses at the specific organ. For the estimate of doses to the blood forming organs (BFOs), data on active marrow distributions in adult were used to weight the bone marrow sites over the human body. The discrete number of target points of MAX organs resulted in a reduced organ dose and dose equivalent compared to the results of CAM organs especially for SPE, and should be further investigated. Differences of effective doses between the two approaches were found to be small (<5%) for GCR.     

Organ shielding and doses in Low-Earth orbit calculated for spherical and anthropomorphic phantoms

Humans in space are exposed to elevated levels of radiation compared to ground. Different sources contribute to the total exposure with galactic cosmic rays being the most important component. The application of numerical and anthropomorphic phantoms in simulations allows the estimation of dose rates from galactic cosmic rays in individual organs and whole body quantities such as the effective dose. The male and female reference phantoms defined by the International Commission on Radiological Protection and the hermaphrodite numerical RANDO phantom are voxel implementations of anthropomorphic phantoms and contain all organs relevant for radiation risk assessment. These anthropomorphic phantoms together with a spherical water phantom were used in this work to translate the mean shielding of organs in the different anthropomorphic voxel phantoms into positions in the spherical phantom. This relation allows using a water sphere as surrogate for the anthropomorphic phantoms in both simulations and measurements. Moreover, using spherical phantoms in the calculation of radiation exposure offers great advantages over anthropomorphic phantoms in terms of computational time.     

实时仿真中的逼真虚拟地球实现

针对虚拟现实中真实感不强的问题,提出了一种具有高精度地表纹理的虚拟地球实现方法,构建了一个地表纹理像素精度高达21 600像素×10 800像素、地球表面轮廓凹凸效果和大气层光晕效果的虚拟地球.采用几何计算来构建地球形状模型,将地球按经纬度分成128块,分别计算每块区域顶点坐标、法向量、纹理坐标;采用混合纹理技术对地表纹理、云层纹理及云层法向量图进行3层纹理混合实现地球表面的云层和轮廓凹凸效果;采用实时移动与放缩带大气层纹理的正方形面板来实现大气光晕效果;采用可见性判断和纹理精度管理的方法,实时判断地球表面区域的可见性、选择不同精度纹理粘贴、剔除不可见区域,减少绘制开销.实验显示,该方法在加载1.02 GB纹理像素的情况下,达到了45帧/s的帧速率.      

The role of computerized modeling and simulation in the development of life support system technologies.

Using conventional means of process development, it would take decades and hundreds of millions of dollars to develop technology for recycling of water and solid waste for lunar missions within the next thirty years. Since we anticipate neither that amount of time nor level of funding, new methodologies for developing life support systems (LSS) technologies are essential. Computerized modeling and simulation (CMAS) is a tool that can greatly reduce both the time and cost of technology development. By CMAS, we refer to computer methods for correlating, storing and retrieving property data for chemical species and for solving the phenomenological equations of physical/chemical processes (i.e., process conditions based on properties of materials and mass and energy balances, equipment sizing based on rate processes and the governing equations for unit operations). In particular, CMAS systems can be used to evaluate a LSS process design with minimal requirements for laboratory experimentation. A CMAS model using ASPEN PLUS is presented for a vapor compression distillation (VCD) system designed for reclaiming water from urine.     

Helium-ion-induced human cataractogenesis.

Retrospective and ongoing analyses of clinical records from 347 primary intraocular melanoma patients treated with helium ions at LBL will allow examination of the exposure-response data for human cataract; which is a complication of the therapy from incidental exposure of the lens. Direct particle beam traversal of at least a portion of the lens usually is unavoidable in treatment of posterior intraocular tumors. The precise treatment planned for each patient permits quantitative assessment of the lenticular dose and its radiation quality. We are reporting our preliminary results on the development of helium-ion-induced lens opacifications and cataracts in 54 of these patients who had 10% or less of their lens in the treatment field. We believe these studies will be relevant to estimating the human risk for cataract in space flight.     

Deep space environments for human exploration.

Mission scenarios outside the Earth's protective magnetic shield are being studied. Included are high usage assets in the near-Earth environment for casual trips, for research, and for commercial/operational platforms, in which career exposures will be multi-mission determined over the astronaut's lifetime. The operational platforms will serve as launching points for deep space exploration missions, characterized by a single long-duration mission during the astronaut's career. The exploration beyond these operational platforms will include missions to planets, asteroids, and planetary satellites. The interplanetary environment is evaluated using convective diffusion theory. Local environments for each celestial body are modeled by using results from the most recent targeted spacecraft, and integrated into the design environments. Design scenarios are then evaluated for these missions. The underlying assumptions in arriving at the model environments and their impact on mission exposures within various shield materials will be discussed.     

Radiation risk and human space exploration.

Radiation protection is essential to enable humans to live and work safely in space. Predictions about the nature and magnitude of the risks posed by space radiation are subject to very large uncertainties. Prudent use of worst-case scenarios may impose unacceptable constraints on shielding mass for spacecraft or habitats, tours of duty of crews on Space Station, and on the radius and duration of sorties on planetary surfaces. The NASA Space Radiation Health Program has been devised to develop the knowledge required to accurately predict and to efficiently manage radiation risk. The knowledge will be acquired by means of a peer-reviewed, largely ground-based and investigator-initiated, basic science research program. The NASA Strategic Plan to accomplish these objectives in a manner consistent with the high priority assigned to the protection and health maintenance of crews will be presented.     

Science strategy for human exploration of Mars.

The scientific objectives of Mars exploration can be framed within the overarching theme of exploring Mars as another home for life, both for evidence of past or present life on Mars, and as a potential future home for human life. The two major areas of research within this theme are: 1) determining the relationship between planetary evolution, climate change, and life, and 2) determining the habitability of Mars. Within this framework, this paper discusses the exploration objectives for exobiology, climatology and atmospheric science, geology, and martian resource assessment. Human exploration will proceed in four major phases: 1) Precursor missions which will obtain environmental knowledge necessary for human exploration, 2) Emplacement phase which includes the first few human landings where crews will explore the local area of the landing site; 3) Consolidation phase missions where a permanent base will be constructed and crews will be capable of detailed exploration over regional scales; 4) Utilization phase, in which a continuously occupied permanent Mars base exists and humans will be capable of detailed global exploration of the martian surface. The phases of exploration differ primarily in the range and capabilities of human mobility. In the emplacement phase, an unpressurized rover, similar to the Apollo lunar rover, will be used and will have a range of a few tens of kilometers. In the Consolidation phase, mobility will be via a pressurized all-terrain vehicle capable of expeditions from the base site of several weeks duration. In the Utilization phase, humans will be capable of several months long expeditions to any point on the surface of Mars using a suborbital rocket equipped with habitat, lab, and return vehicle. Because of human mobility limitations, it is important to extend the range and duration of exploration in all phases by using teleoperated rover vehicles. Site selection for human missions to Mars must consider the multi-decade time frame of these four phases. We suggest that operations in the first two phases be focused in the regional area containing the Coprates Quadrangle and adjacent areas.     

How human sleep in space--investigations during space flights.

Sleep problems have been observed during many of the space flights. The existence of poor quality of sleep, fatigue, insomnia or different alterations in sleep structure, organization and sleep cyclicity have been established. Nevertheless results obtained from investigations of human sleep on board manned space vehicles show that it is possible to keep sleep patterns related to the restorative and adaptive processes. For the first time in the frame of the "Intercosmos" program a multi-channel system for recording and analysis of sleep in space was constructed by scientists of the Bulgarian Academy of Sciences and was installed on board the manned Mir orbiting station. In 1988 during the joint Bulgarian-Russian space flight continues recording of electro-physiological parameters necessary to estimate the sleep stages and sleep organization was made. These investigations were continued in next space flights of different prolongation. The results were compared with the findings obtained under the conditions during the pre- and post-flight periods.     

Radiation-induced chromosomal instability in human mammary epithelial cells.

Karyotypes of human cells surviving X- and alpha-irradiation have been studied. Human mammary epithelial cells of the immortal, non-tumorigenic cell line H184B5 F5-1 M/10 were irradiated and surviving clones isolated and expanded in culture. Cytogenetic analysis was performed using dedicated software with an image analyzer. We have found that both high- and low-LET radiation induced chromosomal instability in long-term cultures, but with different characteristics. Complex chromosomal rearrangements were observed after X-rays, while chromosome loss predominated after alpha-particles. Deletions were observed in both cases. In clones derived from cells exposed to alpha-particles, some cells showed extensive chromosome breaking and double minutes. Genomic instability was correlated to delayed reproductive death and neoplastic transformation. These results indicate that chromosomal instability is a radiation-quality-dependent effect which could determine late genetic effects, and should therefore be carefully considered in the evaluation of risk for space missions.     

Cultures of human liver cells in simulated microgravity environment.

We used microgravity-simulated bioreactors that create the unique environment of low shear force and high-mass transfer to establish long-term cultures of primary human liver cells (HLC). To assess the feasibility of establishing HLC cultures, human liver cells obtained either from cells dissociated by collagenase perfusion or minced tissues were cultured in rotating vessels. Formation of multidimensional tissue-like spheroids (up to 1.0 cm) comprised of hepatocytes and biliary epithelial cells that arranged as bile duct-like structures along newly formed vascular sprouts were observed. Electron microscopy revealed clusters of round hepatocytes and bile canaliculi with multiple microvilli and tight junctions. Scanning EM revealed rounded hepatocytes that were organized in tight clusters surrounded by a complex mesh of extracellular matrix. Also, we observed that co-culture of hepatocytes with endothelial cells stimulate albumin mRNA expression. In summary, a simulated microgravity environment is conducive for the establishment of long-term HLC cultures and allows the dissection of the mechanism of liver regeneration and cell-to-cell interactions that resembles in vivo conditions.     

Planetary protection issues in advance of human exploration of Mars.

Current planetary quarantine considerations focus on robotic missions and attempt a policy of no biological contamination. The presence of humans on Mars, however, will inevitably result in biological contamination and physical alteration of the local environment. The focus of planetary quarantine must therefore shift toward defining and minimizing the inevitable contamination associated with humans. This will involve first determining those areas that will be affected by the presence of a human base, then verifying that these environments do not harbor indigenous life nor provide sites for Earth bacteria to grow. Precursor missions can provide salient information that can make more efficient the planning and design of human exploration missions. In particular, a robotic sample return mission can help to eliminate the concern about returning samples with humans or the return of humans themselves from a planetary quarantine perspective. Without a robotic return the cost of quarantine that would have to be added to a human mission may well exceed the cost of a robotic return mission. Even if the preponderance of scientific evidence argues against the presence of indigenous life, it must be considered as part of any serious planetary quarantine analysis for missions to Mars. If there is life on Mars, the question of human exploration assumes an ethical dimension.     

Mutation induction in human lymphoid cells by energetic heavy ions.

One of the concerns for extended space flight outside the magnetosphere is exposure to galactic cosmic radiation. In the series of studies presented herein, the mutagenic effectiveness of high energy heavy ions is examined using human B-lymphoblastoid cells across an LET range from 32keV/micrometer to 190 keV/micrometer. Mutations were scored for an autosomal locus, thymidine kinase (tk), and for an X-linked locus, hypoxanthine phosphoribosyltransferase (hprt). For each of the radiations studied, the autosomal locus is more sensitive to mutation induction than is the X-linked locus. When mutational yields are expressed in terms of particle fluence, the two loci respond quite differently across the range of LET. The action cross section for mutation induction peaks at 61 keV/micrometer for the tk locus and then declines for particles of higher LET, including Fe ions. For the hprt locus, the action cross section for mutation is maximal at 95 keV/micrometer but is relatively constant across the range from 61 keV/micrometer to 190 keV/micrometer. The yields of hprt-deficient mutants obtained after HZE exposure to TK6 lymphoblasts may be compared directly with published data on the induction of hprt-deficient mutants in human neonatal fibroblasts exposed to similar ions. The action cross section for induction of hprt-deficient mutants by energetic Fe ions is more than 10-fold lower for lymphoblastoid cells than for fibroblasts.     

Weightlessness acts on human breast cancer cell line MCF-7.

Because cells are sensitive to mechanical forces, weightlessness might act on stress-dependent cell changes. Human breast cancer cells MCF-7, flown in space in a Photon capsule, were fixed after 1.5, 22 and 48 h in orbit. Cells subjected to weightlessness were compared to 1 g in-flight and ground controls. Post-flight, fluorescent labeling was performed to visualize cell proliferation (Ki-67), three cytoskeleton components and chromatin structure. Confocal microscopy and image analysis were used to quantify cycling cells and mitosis, modifications of the cytokeratin network and chromatin structure. Several main phenomena were observed in weightlessness: The perinuclear cytokeratin network and chromatin structure were looser; More cells were cycling and mitosis was prolonged. Finally, cell proliferation was reduced as a consequence of a cell-cycle blockade; Microtubules were altered in many cells. The results reported in the first point are in agreement with basic predictions of cellular tensegrity. The prolongation of mitosis can be explained by an alteration of microtubules. We discuss here the different mechanisms involved in weightlessness alteration of microtubules: i) alteration of their self-organization by reaction-diffusion processes, and a mathematical model is proposed, ii) activation or deactivation of microtubules stabilizing proteins, acting on both microtubule and microfilament networks in cell cortex.     

On statistical relationship of solar, geomagnetic and human activities.

Data of galactic cosmic rays, solar and geomagnetic activities and solar wind parameters on the one side and car accident events (CAE) in Poland on the other have been analyzed in order to reveal the statistical relationships among them for the period of 1990-2001. Cross correlation and cross spectrum of the galactic cosmic ray intensity, the solar wind (SW) velocity, Kp index of geomagnetic activity and CAE in Poland have been carried out. It is shown that in some epochs of the above-mentioned period there is found a reliable relationship between CAE and solar and geomagnetic activities parameters in the range of the different periodicities, especially, 7 days. The periodicity of 7 days revealed in the data of the CAE has the maximum on Friday without any exception for the minimum and maximum epochs of solar activity. However, the periodicity of 7 days is reliably revealed in other parameters characterizing galactic cosmic rays, SW, solar and geomagnetic activities, especially for the minimum epoch of solar activity. The periodicity of 3.5 days found in the series of CAE data more or less can be completely ascribed to the social effects, while the periodicity of 7 days can be ascribed to the social effect or/to the processes on the Sun, in the interplanetary space and in the Earth's magnetosphere and atmosphere.     

Gravitational effects on human cardiovascular responses to isometric muscle contractions.

Isometric exercise induces profound cardiovascular adaptations increasing mean arterial pressure and heart rate. We investigated effects of simulated +Gz and -Gz respectively on the central and peripheral cardiovascular system. Sustained handgrip exercise was performed at 40% of maximum for 2 minutes in five subjects. This maneuver increased mean arterial pressure by 40-45 mm Hg both during head out water immersion which simulates weightlessness, as well as bedrest during -25, 0, and +25 degrees tilt from the horizontal. Lower body negative pressure (-60 mm Hg for 10 min) attenuated the response to handgrip exercise to 30 mm Hg. It also increased the heart rate minimally by about 20 beats per minute while the water immersion, as well as head up, head down and horizontal bedrest showed increments of about 50 beats per min. It was concluded that the response to isometric contraction is mediated through the high pressure baroreceptors, because similar responses were seen during stresses producing a wide variation in central venous pressure. During lower body negative pressure the increased sympathetic nervous activity itself increased resting heart rate and mean arterial pressure. The responses to static exercise were, therefore, weaker.     

Charged-particle mutagenesis II. Mutagenic effects of high energy charged particles in normal human fibroblasts.

The biological effects of high LET charged particles are a subject of great concern with regard to the prediction of radiation risk in space. In this report, mutagenic effects of high LET charged particles are quantitatively measured using primary cultures of human skin fibroblasts, and the spectrum of induced mutations are analyzed. The LET of the charged particles ranged from 25 KeV/micrometer to 975 KeV/micrometer with particle energy (on the cells) between 94-603 MeV/u. The X-chromosome linked hypoxanthine guanine phosphoribosyl transferase (hprt) locus was used as the target gene. Exposure to these high LET charged particles resulted in exponential survival curves; whereas, mutation induction was fitted by a linear model. The Relative Biological Effect (RBE) for cell-killing ranged from 3.73 to 1.25, while that for mutant induction ranged from 5.74 to 0.48. Maximum RBE values were obtained at the LET of 150 keV/micrometer. The inactivation cross-section (alpha i) and the action cross-section for mutant induction (alpha m) ranged from 2.2 to 92.0 micrometer2 and 0.09 to 5.56 x 10(-3) micrometer2, respectively. The maximum values were obtained by 56Fe with an LET of 200 keV/micrometer. The mutagenicity (alpha m/alpha i) ranged from 2.05 to 7.99 x 10(-5) with the maximum value at 150 keV/micrometer. Furthermore, molecular analysis of mutants induced by charged particles indicates that higher LET beams are more likely to cause larger deletions in the hprt locus.     

Development of human epithelial cell systems for radiation risk assessment.

The most important health effect of space radiation for astronauts is cancer induction. For radiation risk assessment, an understanding of carcinogenic effect of heavy ions in human cells is most essential. In our laboratory, we have successfully developed a human mammary epithelial cell system for studying the neoplastic transformation in vitro. Growth variants were obtained from heavy ion irradiated immortal mammary cell line. These cloned growth variants can grow in regular tissue culture media and maintain anchorage dependent growth and density inhibition property. Upon further irradiation with high-LET radiation, transformed foci were found. Experimental results from these studies suggest that multiexposure of radiation is required to induce neoplastic transformation of human epithelial cells. This multihits requirement may be due to high genomic stability of human cells. These growth variants can be useful model systems for space flight experiments to determine the carcinogenic effect of space radiation in human epithelial cells.