Monte Carlo simulation of the effect of magnetic fields on brachytherapy dose distributions in lung tissue material.

The aim of this work was to use TOPAS Monte Carlo simulations to model the effect of magnetic fields on dose distributions in brachytherapy lung treatments, under ideal and clinical conditions. Idealistic studies were modeled consisting of either a monoenergetic electron source of 432 keV, or a polyenergetic electron source using the spectrum of secondary electrons produced by 192Ir gamma-ray irradiation. The electron source was positioned in the center of a homogeneous, lung tissue phantom (ρ = 0.26 g/cm3). Conversely, the clinical study was simulated using the VariSource VS2000 192Ir source in a patient with a lung tumor. Three contoured volumes were considered: the tumor, the planning tumor volume (PTV), and the lung. In all studies, dose distributions were calculated in the presence or absence of a constant magnetic field of 3T. Also, TG-43 parameters were calculated for the VariSource and compared with published data from EGS-brachy (EGSnrc) and PENELOPE. The magnetic field affected the dose distributions in the idealistic studies. For the monoenergetic and poly-energetic studies, the radial distance of the 10% iso-dose line was reduced in the presence of the magnetic field by 64.9% and 24.6%, respectively. For the clinical study, the magnetic field caused differences of 10% on average in the patient dose distributions. Nevertheless, differences in dose-volume histograms were below 2%. Finally, for TG-43 parameters, the dose-rate constant from TOPAS differed by 0.09% ± 0.33% and 0.18% ± 0.33% with respect to EGS-brachy and PENELOPE, respectively. The geometry and anisotropy functions differed within 1.2% ± 1.1%, and within 0.0% ± 0.3%, respectively. The Lorentz forces inside a 3T magnetic resonance machine during 192Ir brachytherapy treatment of the lung are not large enough to affect the tumor dose distributions significantly, as expected. Nevertheless, large local differences were found in the lung tissue. Applications of this effect are therefore limited by the fact that meaningful differences appeared only in regions containing air, which is not abundant inside the human.

Biokinetics of embedded surrogate radiological dispersal device material.

The terrorist use of a radiological dispersal device (RDD) has been described as "not if, but when" (). Exposures from such an event could occur by a number of routes including inhalation, wound contamination, or embedded fragments. Several of the radionuclides thought to be potential RDD components are metals or ceramic material. The use of such material would increase the potential for wounds from embedded fragments of radioactive material. To date, most research in this area has focused on inhalation exposures, while the consequence of embedded fragment exposure has not been investigated. This study modified a previously used rodent model in order to determine the biokinetics of intramuscularly implanted nonradioactive surrogate RDD material. Cobalt, iridium, or strontium titanate was embedded into the gastrocnemius muscle of Sprague Dawley rats. The rats were euthanized at 1, 3, or 6 mo post-implantation. Tissue metal analysis showed that iridium did not solubilize from the implanted pellet, while cobalt and strontium did so rapidly. Cobalt was found in all tissues analyzed, but it was localized mainly to kidney and liver as well as being excreted in the urine. Strontium was found in lung, liver, and spleen, as well as being deposited in bone. However, the greatest strontium concentrations were found in the popliteal lymph nodes, the lymph nodes responsible for draining the area of the gastrocnemius. These results indicate that, depending upon the material, a variety of treatment strategies will be needed when dealing with embedded fragment wounds from a radiological dispersal device event.

Long-term clearance kinetics of inhaled ultrafine insoluble iridium particles from the rat lung, including transient translocation into secondary organs.

Recently it was speculated that ultrafine particles (UFP) may translocate from deposition sites in the lungs to systemic circulation and whether long-term clearance differs between ultrafine and micrometer-sized particles. We have studied lung retention and clearance kinetics in 12 healthy male adult WKY rats up to 6 mo after an inhalation of (192)Ir-radiolabeled, insoluble, ultrafine 15- to 20-nm iridium particles. Whole-body retention was followed by external gamma counting, and particle clearance kinetics were determined by excretion radioanalysis. Four rats each were sacrificed after 3 wk and 2 and 6 mo; all organs as well as tissues and the carcass were radioanalyzed to balance the entire deposited radioactivity of the particles. The most prominent fraction was retained in the lungs at each time point of sacrifice (26%, 15%, 6%, respectively), and clearance out of the body was solely via excretion. Extrapulmonary particle uptake did not continue to increase but decreased with time in liver, spleen, heart, and brain when compared to previous data obtained during the first 7 days after inhalation (Kreyling et al., 2002). UFP long-term lung retention derived from whole-body measurements was comparable to previously reported data using insoluble micrometer-sized particles (Bellmann et al., 1994; Lehnert et al., 1989). In addition, differential analysis including daily excretion data revealed a pattern of fractional particle clearance rate of the ultrafine iridium particles similar to that of micrometer-sized particles reported by Snipes et al. (1983) and Bailey et al. (1985).

Patient effective dose from endovascular brachytherapy with 192Ir sources.

The growing use of endovascular brachytherapy has been accompanied by the publication of a large number of studies in several fields, but few studies on patient dose have been found in the literature. Moreover, these studies were carried out on the basis of Monte Carlo simulation. The aim of the present study was to estimate the effective dose to the patient undergoing endovascular brachytherapy treatment with 112Ir sources, by means of experimental measurements. Two standard treatments were taken into account: an endovascular brachytherapy of the coronary artery corresponding to the activity x time product of 184 GBq.min and an endovascular brachytherapy of the renal artery (898 GBq.min). Experimental assessment was accomplished by thermoluminescence dosemeters positioned in more than 300 measurement points in a properly adapted Rqndo phantom. A method has been developed to estimate the mean organ doses for all tissues and organs concerned in order to calculate the effective dose associated with intravascular brachytherapy. The normalised organ doses resulting from cronary treatment were 2.4 x 10(-2) mSv.GBq(-1).min(-1) for lung, 0.9 x 10(-2) mSv.GBSq(-1).min(-1) for oesophagus and 0.48 x 10(-2) mS.GBq(-1).min(-1) for bone marrow. During brachytherapy of the renal artery, the corresponding normalised doses were 4.2 x 10(-2) mS.GBq(-1).min(-1) for colon, 7.8 x 10(-2) mSv.GBq(-1).min(-1) for stomach and 1.7 x 10(-2) mSv.GBq(-1).min(-1) for liver. Coronary treatment iJnvlled an efl'fective dose of (0.046 mSv.GBq(-1).min(-1), whereas the treatment of the renal artery resulted in an effective dose of 0.15 mSv.GBq(-1).min(-1); there were many similarities with data from former studies. Based on these results it can be concluded that the dose level of patients exposed during brachytherapy treatment is low.

Ytterbium-169: a promising new radionuclide for intravascular brachytherapy.

PURPOSE: To explore the feasibility of 169Yb (gamma, 93 keV) as a new radionuclide for intravascular brachytherapy (IVBT) in terms of dose distribution, penetration power, and radiation safety features as compared with 125I and 192Ir. METHODS: The dose distributions for catheter-based sources, 169Yb, 125I, and 192Ir, in homogeneous water and in the presence of calcium and a steel stent have been determined and compared using the Monte Carlo method (MCNP4B2 code). The dose rates of the sources were evaluated from 0.02 to 100 cm. RESULTS: In the short distance range (0.02

192IrCl acid skin burn: case report and review of the literature.

A worker was contaminated following a chemical explosion that splashed an HNO3 radioactive solution containing approximately 180 MBq (5 mCi) 192Ir onto the left side of his face. Initial efforts reduced the contamination at least fivefold. Removal of a patch of contaminated hair was necessary. Most of the contamination was fixed to the skin; only a small amount of contamination was absorbed.

[191mIr: distribution and retention in animal experiments]. / 191mIr: Verteilung und Retention im Tierversuch.

Ultrashort-lived tracer 191mIr (T1/2 = 4.92 s) can be obtained with a high yield from an 191Os/191mIr generator with a low 191Os breakthrough. It was eluated directly into the tail veins of Wistar rats. These animals were imaged dynamically (five frames/s) up to 40 s. The measurement was repeated five times on each animal. The whole-body retention and biodistribution of 191Os was studied by sacrificing the rats at one and four days, respectively, after injection. The activity retained was highest in the kidneys and the spleen, followed by the muscles and the liver. These values indicate that the breakthrough is by no means dangerous and that investigations can be repeated immediately with a radiation exposure of no significance. Furthermore, all investigations in the same animal were reproducible, suggesting that 191mIr might be a good tracer for nuclear angiograms.