Monte Carlo modeling of the effects of injected short-, medium- and longer-range alpha-particle emitters on human marrow at various ages.

The effects of injected short-, medium- and longer-range alpha-particle emitters ((149)Tb, (211)At/(211)Po and (213)Bi/(213)Po, respectively) on the total hemopoietic stem cell population of active normal bone marrow in humans of various ages has been estimated using Monte Carlo modeling. The fraction of the normal hemopoietic stem cells that are hit and survive has been calculated as a first step toward estimating the risk of development of therapy-induced leukemia. The fraction was lowest for the shorter-range alpha-particle emitter ((149)Tb) and highest for the longer-range alpha-particle emitter ((213)Bi/(213)Po), with the value for the medium-range alpha-particle emitter (211)At/(211)Po being intermediate between these. There was little variation in the data with the age of the subject within each alpha-particle emitter. This lack of age dependence provides reassurance that the fraction of cells hit in any subject of any age with normal marrow can be estimated by modeling newborn marrow (which requires little computing time) despite age-related differences in microarchitecture.

Effect of global system for mobile communication (gsm)-like radiofrequency fields on vascular permeability in mouse brain.

The effect of global system for mobile communication (GSM) radiofrequency fields on vascular permeability in the brain was studied using a purpose-designed exposure system at 898.4 MHz. Mice (n= 30) were given a single far field, whole body exposure for 60 minutes at a specific absorption rate of 4 W/kg. Control mice were also sham-exposed (n = 10) or permitted free movement in a cage (n = 10) to exclude any stress-related effects. Vascular permeability changes were detected using albumin immunohistochemistry and the efficacy of this vascular tracer was confirmed with a positive control group exposed to a clostridial toxin known to increase vascular permeability in the brain. No significant difference in albumin extravasation was detected between any of the groups at the light microscope level using the albumin marker.

Theoretical treatment of human haemopoietic stem cell survival following irradiation by alpha particles.

PURPOSE: To calculate survival of human haemopoietic stem cells irradiated by alpha particles from 149Tb (initial energy 3.97 MeV) and 211At (average initial energy 6.87 MeV). METHODS: Following as closely as possible radiobiological data, Monte Carlo methods were used to calculate passages of alpha particles (originating in three geometries) through the nuclei of haemopoietic stem cells. Survival of stem cell populations was calculated from the probability of surviving each passage (a function of LET). RESULTS: For decays targeted to the surface of individual cells 37% survival was found at 1.3 passages per nucleus for 149Tb and 6.5 for 211At/Po decays. For decays distributed in a large volume the D0 doses were 0.81 and 0.87 for 149Tb and 211At respectively. When 36% of the marrow is occupied by fat cells alphas from 149Tb are more effective with a D0 of 0.68Gy compared to 0.82Gy for the 211At/Po combination. CONCLUSIONS: When the isotopes are targeted to the cell, in terms of passages, 149Tb is five times more effective at cell killing than 211At, which when expressed in terms of dose, increases to a factor of 9. When the isotopes are broadly distributed (such as in marrow or in vitro) the differences are considerably reduced.

Monte Carlo/numerical treatment of alpha-particle spectra from sources buried in bone and resultant doses to surface cells.

PURPOSE: To calculate the depth distribution of radioactive decays in bone by fitting a calculated alpha-particle energy spectrum to a measured spectrum. The dose to bone surface cells is then calculated from the depth distribution. MATERIALS AND METHODS: The spectra are calculated using Monte Carlo methods and a numerical depth distribution obtained by trial and error. RESULTS: Alpha spectra for 210Po and 226Ra (plus decay products) in bone were calculated and fitted to experimental spectra. The dose to bone surface cells was calculated using the numerical technique and compared to previously published data. CONCLUSIONS: Alpha-particle spectra can be successful fitted using this method, which gives a more realistic distribution of decays with depth than simple surface and volume models.

Microdosimetry of haemopoietic stem cells irradiated by alpha particles from the short-lived products of 222Rn decays in fat cells and haemopoietic tissue.

The Monte Carlo method is used to model fat cells and the nuclei of stem cells in haemopoietic tissue where 222Rn is dissolved in different amounts in the fat and tissue. Calculations are performed for fat cells of diameters 50 and 100 microns and for stem cell nuclei of 8 and 16 microns diameters for various fractions of fat filling the volume. Average doses (and their distributions) to stem cell nuclei from single passages of alpha particles are presented. In addition to dose, the relationship between LET and dose is obtained, illustrating the importance of 'stoppers' in the calculations. The annual average dose equivalent for a concentration of 1 Bq/m3 in air agrees well with other authors at 12 mu Sv/year. The method also allows the calculation of the fraction of stem cell nuclei hit annually. Here for 1 Bq/m3, stem cell nuclei of diameter 8 microns and 100% fat filing 15 x 10(-7) of the stem cell nuclei are hit.

Monte Carlo modelling of neutron depth dose distributions in optimizing prompt gamma in vivo neutron activation analysis systems.

Optimization of prompt gamma in vivo neutron activation analysis systems is best achieved using Monte Carlo simulation. In this study the modelling of the dimensions and materials for source holders and collimators is described and compared with experimentally derived results where feasible. Results show that valid depth doses are obtained by modelling only the central part of an IVNAA system and that the use of borated paraffin as a reflector provides acceptable thermal fluence and depth dose.