RESUMEN
Crews of high-altitude aircraft are exposed to radiation from galactic cosmic rays (GCRs). To help determine such exposures, the Atmospheric Ionizing Radiation Project, an international collaboration of 15 laboratories, made simultaneous radiation measurements with 14 instruments on a NASA ER-2 high-altitude airplane. The primary instrument was a sensitive extended-energy multisphere neutron spectrometer. Its detector responses were calculated for energies up to 100 GeV using the radiation transport code MCNPX 2.5.d with improved nuclear models and including the effects of the airplane structure. New calculations of GCR-induced particle spectra in the atmosphere were used to correct for spectrometer counts produced by protons, pions and light nuclear ions. Neutron spectra were unfolded from the corrected measured count rates using the deconvolution code MAXED 3.1. The results for the measured cosmic-ray neutron spectrum (thermal to >10 GeV), total neutron fluence rate, and neutron dose equivalent and effective dose rates, and their dependence on altitude and geomagnetic cut-off agree well with results from recent calculations of GCR-induced neutron spectra.
Asunto(s)
Aeronaves/estadística & datos numéricos , Algoritmos , Radiación Cósmica , Neutrones , Exposición Profesional/análisis , Exposición Profesional/estadística & datos numéricos , Radiometría/estadística & datos numéricos , Altitud , Carga Corporal (Radioterapia) , Exposición a Riesgos Ambientales/análisis , Diseño de Equipo , Geografía/métodos , Internacionalidad , Dosis de Radiación , Protección Radiológica/métodos , Radioisótopos/análisis , Radiometría/métodos , Efectividad Biológica Relativa , Reproducibilidad de los Resultados , Medición de Riesgo/métodos , Factores de Riesgo , Sensibilidad y EspecificidadRESUMEN
The propagation of primary cosmic rays through the Earth's atmosphere and the energy spectra of the resulting secondary particles have been calculated using the Monte Carlo transport code FLUKA with several novel auxiliary methods. Solar-modulated primary cosmic ray spectra were determined through an analysis of simultaneous proton and helium measurements made on spacecraft or high-altitude balloon flights. Primary protons and helium ions are generated within the rigidity range of 0.5 GV-20 TV, uniform in cos2theta. For a given location, primaries above the effective angle-dependent geomagnetic cut-off rigidity, and re-entrant albedo protons, are transported through the atmosphere. Helium ions are initially transported using a separate transport code called HEAVY to simulate fragmentation. HEAVY interfaces with FLUKA to provide interaction starting points for each nucleon originating from a helium nucleus. Calculated cosmic ray neutron spectra and consequent dosimetric quantities for locations with a wide range of altitude (atmospheric depth) and geomagnetic cut-off are presented and compared with measurements made on a high-altitude aeroplane. Helium ion propagation using HEAVY and inclusion of re-entrant albedo protons with the incident primary spectra significantly improved the agreement of the calculated cosmic ray neutron spectra with measured spectra. These cosmic ray propagation calculations provide the basis for a new atmospheric ionising radiation (AIR) model for air-crew dosimetry, calculation of effects on microelectronics, production of cosmogenic radionuclides and other uses.
Asunto(s)
Algoritmos , Atmósfera/análisis , Radiación Cósmica , Modelos Teóricos , Neutrones , Radiometría/métodos , Análisis Espectral/métodos , Simulación por Computador , Unión Europea , Dosis de Radiación , Protección Radiológica/métodos , Reproducibilidad de los Resultados , Medición de Riesgo/métodos , Factores de Riesgo , Sensibilidad y EspecificidadRESUMEN
A new Atmospheric Ionizing Radiation (AIR) model is currently being developed for use in radiation dose evaluation in epidemiological studies targeted to atmospheric flight personnel such as civilian airlines crewmembers. The model will allow computing values for biologically relevant parameters, e.g. dose equivalent and effective dose, for individual flights from 1945. Each flight is described by its actual three dimensional flight profile, i.e. geographic coordinates and altitudes varying with time. Solar modulated primary particles are filtered with a new analytical fully angular dependent geomagnetic cut off rigidity model, as a function of latitude, longitude, arrival direction, altitude and time. The particle transport results have been obtained with a technique based on the three-dimensional Monte Carlo transport code FLUKA, with a special procedure to deal with HZE particles. Particle fluxes are transformed into dose-related quantities and then integrated all along the flight path to obtain the overall flight dose. Preliminary validations of the particle transport technique using data from the AIR Project ER-2 flight campaign of measurements are encouraging. Future efforts will deal with modeling of the effects of the aircraft structure as well as inclusion of solar particle events.
Asunto(s)
Atmósfera , Aviación , Radiación Cósmica , Modelos Teóricos , Método de Montecarlo , Exposición Profesional , Medicina Aeroespacial , Bases de Datos Factuales , Partículas Elementales , Humanos , Magnetismo , Fantasmas de Imagen , Dosis de Radiación , Radiometría , Medición de RiesgoRESUMEN
The Supersonic Transport (SST) program, proposed in 1961, first raised concern for the exposure of pregnant occupants by solar energetic particles (SEP), and neutrons were suspected to have a main role in particle propagation deep into the atmosphere. An eight-year flight program confirmed the role of SEP as a significant hazard and of the neutrons as contributing over half of the galactic cosmic ray exposures, with the largest contribution from neutrons above 10 MeV. The FAA Advisory Committee on the Radiobiological Aspects of the SST provided operational requirements. The more recent lowering of ICRP-recommended exposure limits (1990) with the classification of aircrew as "radiation workers" renewed interest in GCR background exposures at commercial flight altitudes and stimulated epidemiological studies in Europe, Japan, Canada and the USA. The proposed development of a High Speed Civil Transport (HSCT) required validation of the role of high-energy neutrons, and this resulted in ER-2 flights at solar minimum (June 1997) and studies on effects of aircraft materials on interior exposures. Recent evaluation of health outcomes of DOE nuclear workers resulted in legislation for health compensation in year 2000 and recent European aircrew epidemiological studies of health outcomes bring renewed interest in aircraft radiation exposures. As improved radiation models become available, it is imperative that a corresponding epidemiological program of US aircrew be implemented.
Asunto(s)
Aviación/normas , Radiación Cósmica , Neutrones , Protección Radiológica/normas , Actividad Solar , Medicina Aeroespacial , Femenino , Humanos , Masculino , Neoplasias Inducidas por Radiación/epidemiología , Exposición Profesional , Embarazo , Dosis de RadiaciónRESUMEN
Crews of future high-altitude commercial aircraft may be significantly exposed to atmospheric cosmic radiation from galactic cosmic rays (GCR). To help determine such exposures, the Atmospheric Ionizing Radiation Project, an international collaboration of 15 laboratories, made simultaneous radiation measurements with 14 instruments on a NASA ER-2 high-altitude aircraft. The primary instrument was a sensitive extended-energy multisphere neutron spectrometer, which was also used to make measurements on the ground. Its detector responses were calculated for neutrons and charged hadrons at energies up to 100 GeV using the radiation transport code MCNPX. We have now recalculated the detector responses including the effects of the airplane structure. We are also using new FLUKA calculations of GCR-induced hadron spectra in the atmosphere to correct for spectrometer counts produced by charged hadrons. Neutron spectra are unfolded from the corrected measured count rates using the MAXED code. Results for the measured cosmic-ray neutron spectrum (thermal to >10 GeV), total neutron fluence rate, and neutron dose equivalent and effective dose rates, and their dependence on altitude and geomagnetic cutoff generally agree well with results from recent calculations of GCR-induced neutron spectra.
Asunto(s)
Aeronaves/instrumentación , Radiación Cósmica , Neutrones , Exposición Profesional , Monitoreo de Radiación/instrumentación , Altitud , Humanos , Modelos Teóricos , Dosis de RadiaciónRESUMEN
Crews working on present-day jet aircraft are a large occupationally exposed group with a relatively high average effective dose from galactic cosmic radiation. Crews of future high-speed commercial aircraft flying at higher altitudes would be even more exposed. To help reduce the significant uncertainties in calculations of such exposures, the atmospheric ionizing radiation (AIR) project, an international collaboration of 15 laboratories, made simultaneous radiation measurements with 14 instruments on five flights of a NASA ER-2 high-altitude aircraft. The primary AIR instrument was a highly sensitive extended-energy multisphere neutron spectrometer with lead and steel shells placed within the moderators of two of its 14 detectors to enhance response at high energies. Detector responses were calculated for neutrons and charged hadrons at energies up to 100 GeV using MCNPX. Neutron spectra were unfolded from the measured count rates using the new MAXED code. We have measured the cosmic-ray neutron spectrum (thermal to >10 GeV), total neutron fluence rate, and neutron effective dose and dose equivalent rates and their dependence on altitude and geomagnetic cutoff. The measured cosmic-ray neutron spectra have almost no thermal neutrons, a large "evaporation" peak near 1 MeV and a second broad peak near 100 MeV which contributes about 69% of the neutron effective dose. At high altitude, geomagnetic latitude has very little effect on the shape of the spectrum, but it is the dominant variable affecting neutron fluence rate, which was eight times higher at the northernmost measurement location than it was at the southernmost. The shape of the spectrum varied only slightly with altitude from 21 km down to 12 km (56-201 g cm-2 atmospheric depth), but was significantly different on the ground. In all cases, ambient dose equivalent was greater than effective dose for cosmic-ray neutrons.
Asunto(s)
Aeronaves/instrumentación , Altitud , Radiación Cósmica , Neutrones , Monitoreo de Radiación/instrumentación , Medicina Aeroespacial , Aviación , Canadá , Humanos , Cooperación Internacional , Mesones , Protones , Dosis de Radiación , Procesamiento de Señales Asistido por Computador , Análisis Espectral , Estados UnidosRESUMEN
The intensity of the different particles making up atmospheric cosmic radiation, their energy distribution, and their potential biological effect on aircraft occupants vary with altitude, geomagnetic latitude, and time in the sun's magnetic activity cycle. Dose rates from cosmic radiation at commercial aviation altitudes are such that crews working on present-day jet aircraft are an occupationally exposed group with a relatively high average effective dose. Crews of future high speed commercial aircraft flying at higher altitudes would be even more exposed. Present calculations of such exposures are uncertain because knowledge of important components of the radiation field comes primarily from theoretical predictions. To help reduce these uncertainties for high-altitude flight, the National Aeronautics and Space Administration (NASA) and the Department of Energy (DOE) started the Atmospheric Ionizing Radiation (AIR) project. The measurement part of the AIR project is an international collaboration of 12 laboratories placing 14 instruments on multiple flights of a NASA ER-2 aircraft. This paper describes the basic features of cosmic radiation in the atmosphere as they relate to exposure of aircraft occupants and then describes the AIR ER-2 measurements and presents some preliminary results from a series of flights in June 1997.
Asunto(s)
Aeronaves , Radiación Cósmica , Exposición Profesional , Radiometría , Humanos , NeutronesRESUMEN
Reliable neutron dosimetry requires knowledge of the neutron spectrum. We discuss the problem of analyzing data from a multisphere neutron spectrometer to infer the energy spectrum of the incident neutrons and describe the code MAXED, a computer program developed to apply the maximum entropy principle to this problem. The code and documentation are available from the authors upon request.
Asunto(s)
Neutrones , Dosis de Radiación , Radiometría/instrumentación , Radiometría/métodos , Programas Informáticos , Documentación , EntropíaRESUMEN
A previously unreported case of plantar dislocation of the medial cuneiform is described. The significance of this injury does not lie in its rarity, but in the amount of force required to cause such an injury. This large force may cause bony disruption, along with significant soft-tissue injury, and even compartment syndrome. Analysis of the preoperative evaluation, including the importance of a computed axial tomographicscan, operative intervention, and postoperative care are discussed.
Asunto(s)
Fracturas Cerradas/diagnóstico por imagen , Luxaciones Articulares/diagnóstico por imagen , Metatarso/lesiones , Huesos Tarsianos/lesiones , Adulto , Femenino , Fracturas Cerradas/cirugía , Humanos , Luxaciones Articulares/cirugía , Masculino , RadiografíaRESUMEN
Achieving bony union and early weight bearing in peritrochanteric femur fractures poses a continuous challenge for the orthopedic surgeon. Current standards of surgical fixation for the myriad possible fracture patterns include the compression hip screw (CHS), the 90 degrees/95 degrees blade plate, and locked intramedullary nails. The gamma nail (GN) was designed as a "hybrid" of these devices, combining theoretical biomechanical advantages that should allow earlier postoperative weight bearing with surgical technique advantages that should decrease operative morbidity. Because these theoretical advantages were unproven in a clinical setting, we prospectively randomized 75 consecutive patients with peritrochanteric femur fractures into two groups to examine the fixation of these fractures with the GN as compared to the CHS. We found no significant differences in preoperative or intraoperative parameters. Postoperatively, the subtrochanteric fracture group treated with the GN achieved earlier weightbearing status, although this was not statistically significant. 72 patients were available for follow-up at a minimum of 6 months. All fractures had clinically and radiographically healed, and 94% of the patients continued to be ambulatory. Major complications included missed distal locking screws (one patient), cutting out of the lag screw superiorly in the femoral head (two patients), and a femur fracture at the distal end of the GN (one patient). In our series, the GN produced clinical results commensurate with current standards of fixation for peritrochanteric femur fractures. Although the GN allowed earlier independent weightbearing status in patients with subtrochanteric fractures, the procedure was technically more demanding and had a significant learning curve.
Asunto(s)
Clavos Ortopédicos , Tornillos Óseos , Fracturas de Cadera/cirugía , Adulto , Anciano , Anciano de 80 o más Años , Femenino , Curación de Fractura , Humanos , Masculino , Persona de Mediana Edad , Complicaciones Posoperatorias/etiología , Estudios Prospectivos , Soporte de PesoRESUMEN
Subcapital fractures after open reduction and internal fixation of intertrochanteric hip fractures have not previously been attributed to osteomyelitis. We report a unique case of a 63-year-old man with isolated subclinical osteomyelitis of the femoral neck causing ischemic necrosis and subcapital fracture after sliding screw plate fixation of an ipsilateral intertrochanteric fracture.
Asunto(s)
Placas Óseas/efectos adversos , Tornillos Óseos/efectos adversos , Fracturas del Cuello Femoral/etiología , Necrosis de la Cabeza Femoral/etiología , Infecciones por Bacterias Grampositivas/etiología , Fracturas de Cadera/cirugía , Osteomielitis/etiología , Infección de la Herida Quirúrgica/etiología , Antibacterianos/uso terapéutico , Terapia Combinada , Desbridamiento , Fracturas del Cuello Femoral/diagnóstico por imagen , Fracturas del Cuello Femoral/terapia , Necrosis de la Cabeza Femoral/diagnóstico por imagen , Necrosis de la Cabeza Femoral/terapia , Infecciones por Bacterias Grampositivas/diagnóstico por imagen , Infecciones por Bacterias Grampositivas/terapia , Humanos , Masculino , Persona de Mediana Edad , Osteomielitis/diagnóstico por imagen , Osteomielitis/terapia , Radiografía , Infección de la Herida Quirúrgica/diagnóstico por imagen , Infección de la Herida Quirúrgica/terapiaRESUMEN
Aneurysmal bone cysts (ABCs) are relatively uncommon, benign lesions. Fully 50% occur in long bones and 20% in the vertebral column, mostly in patients under 20 years of age. We report a case of an ABC in the odontoid process of a 74-year-old who sought treatment for pain and myelopathy. This is the first case reported of an ABC of the odontoid process.
Asunto(s)
Quistes Óseos/cirugía , Apófisis Odontoides , Anciano , Femenino , HumanosRESUMEN
The relative biological effectiveness (RBE) of photon radiation from encapsulated Iodine-125 "seed" sources has not previously been investigated in human cells. The RBE of 125I photons relative to 137Cs gamma rays was examined in normal diploid human fibroblasts derived from lung and skin. The cells were irradiated in plateau phase using a specially designed incubator-irradiator which permitted simultaneous 125I and 137Cs irradiation. The cells were irradiated at various dose rates ranging from 7 to 70 cGy/hr. Dosimetry was performed using Monte Carlo computer calculations to simulate the 125I irradiations and the exposure-standardization measurements made by the U.S. National Bureau of Standards which are the basis for the specified strengths of 125I seeds. Simulation of the exposure standardization measurements revealed systematic errors due to the unrecognized presence of low-energy fluorescence X rays. The specified activity of the type of seeds used for this study (high-activity, no radiographic marker) was found to be too high by more than 10%. The RBE of 125I assessed with both lung fibroblast lines was found to be 1.2 and was 1.3 for the skin fibroblasts. The RBE did not change over the range of dose rates tested. In fact, for both 125I and 137Cs, the dose response curves did not change with dose rate over the range tested, implying full repair of sublethal damage at dose rates below 70 cGy/hr in these non-dividing cells.
Asunto(s)
Braquiterapia , Radioisótopos de Yodo , Línea Celular , Supervivencia Celular/efectos de la radiación , Radioisótopos de Cesio , Diploidia , Relación Dosis-Respuesta en la Radiación , Fibroblastos/efectos de la radiación , Rayos gamma , Humanos , Técnicas In Vitro , Efectividad Biológica RelativaRESUMEN
Results for inactivation of hydroxyurea-synchronized V-79 cells by ultrasoft aluminum characteristic X rays of energy 1.5 keV are presented. Limiting RBEs at low doses, relative to 137Cs gamma rays, of 1.8 and 6.4 are, respectively, found for cells at the G1/S and late S stages of the cell cycle. The late-S data are analyzed in the light of previous experiments carried out under similar conditions, also designed to probe the effects of energy deposition in nanometer-sized sites, in which cells were irradiated with correlated pairs of ions. Within the framework of the theory of dual radiation action, the results for ultrasoft X rays and gamma rays can be deduced solely from track simulations and the results of the high-LET molecular ion experiment.
Asunto(s)
Células Cultivadas/efectos de la radiación , Animales , Ciclo Celular/efectos de la radiación , División Celular , Supervivencia Celular/efectos de la radiación , Efectividad Biológica Relativa , Rayos XRESUMEN
Apparatus and dosimetry techniques have been developed which make possible studies of the biological effects of radiation from encapsulated 125I sources at clinically relevant dose rates using mammalian cells attached to culture dishes. The variation of dose rate from 125I photons as a function of distance from the interface between different materials was investigated. A polystyrene substrate changes the mean dose rate in attached cells by about 21%, depending on cell thickness. To reduce dosimetry uncertainty caused by this effect, special petri dishes were made from polyvinylidene fluoride, which changes the mean dose in attached cells by only 10%. Chinese hamster ovary cells attached to these dishes were cultured in incubators which contained 125I and 137Cs sources, allowing the effects of various dose rates (.005 to 0.80 Gy/hr) of radiation from the two isotopes to be compared. The relative dose rates from these low- and high-energy photons were measured with an accuracy of +/- 7% or better using an air-equivalent ionization chamber designed to resemble one of our special petri dishes. Calculations of dose rates from 125I give values within 4% of the measured dose rates used to determine the relative biological effectiveness of 125I photons.
Asunto(s)
Radioisótopos de Yodo/administración & dosificación , Dosis de Radiación , Animales , Braquiterapia , Radioisótopos de Cesio , Cricetinae , Femenino , Radiometría , Efectividad Biológica RelativaRESUMEN
Chinese hamster ovary (CHO) cells, in either exponential growth or unfed plateau phase were exposed to graded doses of radiation from Iodine-125 or from Cesium-137 at various dose-rates and the cells were assayed for reproductive integrity. From the patterns of cell survival obtained, the relative biological effectiveness (RBE) of the emission from 125I was determined relative to 137Cs. The RBE determined using cells in exponential growth was found to have a value of about 1.2, which was independent of the level of cell survival and did not vary over the dose-rate range from 7.5 to 53 cGy/hr. Using plateau phase cells the RBE has a constant value of about 1.3 between 13 to 46 cGy/hr, but is closer to 2.0 at lower dose-rates of 5 to 7 cGy/hr.