RESUMEN
Human exposure to space radiation implies two kinds of risk, both stochastic and deterministic. Shielding optimisation therefore represents a crucial goal for long-term missions, especially in deep space. In this context, the use of radiation transport codes coupled with anthropomorphic phantoms allows to simulate typical radiation exposures for astronauts behind different shielding, and to calculate doses to different organs. In this work, the FLUKA Monte Carlo code and two phantoms, a mathematical model and a voxel model, were used, taking the Galactic Cosmic Rays (GCR) spectra from the model of Badhwar and O'Neill. The time integral spectral proton fluence of the August 1972 Solar Particle Event (SPE) was represented by an exponential function. For each aluminium shield thickness, besides total doses the contributions from primary and secondary particles for different organs and tissues were calculated separately. More specifically, organ-averaged absorbed doses, dose equivalents and a form of 'biological dose', defined on the basis of initial (clustered) DNA damage, were calculated. As expected, the SPE doses dramatically decreased with increasing shielding, and doses in internal organs were lower than in skin. The contribution of secondary particles to SPE doses was almost negligible; however it is of note that, at high shielding (10 g cm(-2)), most of the secondaries are neutrons. GCR organ doses remained roughly constant with increasing Al shielding. In contrast to SPE results, for the case of cosmic rays, secondary particles accounted for a significant fraction of the total dose.
Asunto(s)
Radiación Cósmica/efectos adversos , Exposición a Riesgos Ambientales/efectos adversos , Exposición a Riesgos Ambientales/análisis , Modelos Biológicos , Traumatismos por Radiación/etiología , Traumatismos por Radiación/prevención & control , Protección Radiológica/métodos , Astronautas , Simulación por Computador , Relación Dosis-Respuesta en la Radiación , Humanos , Dosis de Radiación , Protección Radiológica/instrumentación , Radiación Ionizante , Medición de Riesgo/métodos , Factores de RiesgoRESUMEN
The outcomes of 1028 assisted reproductive technology cycles were studied retrospectively, considering two different periods of embryo transfer. In the first period, 262 cycles in women < 36 years old were studied, in which three embryos were transferred, followed by 157 cycles in women > or = 36 years, in which four embryos were transferred. In the second period, 332 cycles were evaluated in women < 36 years and 277 cycles in women > or = 36 years old, reducing the number of embryos transferred to two and three respectively. Embryos were only scored morphologically, and the best embryos were chosen for transfer. In the first period, in women < 36 years old, a clinical pregnancy rate of 55.7% was achieved, compared with 42.5% in the second period (P < 0.01). In women > or = 36 years old, the first period of embryo transfer showed a clinical pregnancy rate of 39.5%, compared with 28.5% in the second period (P < 0.01). The number of twin pregnancies in the three groups of patients in whom one to four embryos were transferred was not significantly different (24.2, 28.4, 24.8%). It is concluded that even with the biases induced by a retrospective study, the reduction in the number of embryos transferred, from three to two in women < 36 years of age, and from four to three in women > or = 36 years of age, without any selection other than pre-transfer morphological score, adversely affects the outcome of treatment, without a significant reduction in twin gestation rate. Other strategies are to be implemented in gametes and embryo selection, and patients must be aware that, even with a reduction in pregnancy rate, the goal is to achieve a high cumulative pregnancy rate, reducing the complications induced by multiple pregnancies.