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Purpose Aim of this work was to estimate the radiation absorbed dose to the choroid plexuses in 68Ga-NODAGA-RGD PET, a tracer used to study angiogenic processes that is significantly taken-up by these vascular structures [1]. Methods Five patients who underwent a clinical research protocol of PET-CT with 68Ga-NODAGA-RGD and contrast-enhanced brain MRI were considered for our dosimetric estimations. We set up Monte Carlo simulations in GAMOS (GEANT4-based Architecture for Medicine-Oriented Simulations), which exploited the MRI images as input. In particular, a voxelized region containing choroid plexuses was defined according to the morphological data obtained from the segmentation of MRI images. The radioactive source was uniformly distributed inside the choroid plexuses. A second set of Monte Carlo simulations was carried out using a simplified geometry of choroid plexuses and the results were compared with the MRI-based simulations. A further comparison was made with doses evaluated through the OLINDA sphere model. Results OLINDA sphere model systematically overestimates the dose of about +50% with respect to the MRI-based Monte Carlo simulation. On the other hand, simulations using the simplified geometry show a good agreement with the MRI-based ones. This result is significant, allowing to use short time-consuming calculations and within a simple geometrical environment. Conclusions Because of their markedly elongated and curved morphology, human choroid plexuses are a typical example of tissue structures that cannot be accurately represented by a sphere, when radiation absorbed dose assessments are of concern. Given that the internal dosimetry of choroid plexuses is worth of particular attention when using radiopharmaceuticals that exhibit a selective uptake, Monte Carlo simulation can be regarded as the gold standard for the dosimetry of these structures. [ABSTRACT FROM AUTHOR]

Purpose The aim of this study was to introduce a calculation approach, based on a simple and user-friendly interface to Monte Carlo simulation, for the estimation of the radiation dose to the extremities of the personnel professionally exposed to the ionizing radiations emitted by radionuclides employed in nuclear medicine. Methods Monte Carlo simulations in GAMOS (GEANT4-based Architecture for Medicine-Oriented Simulations) were carried out for 18F, 68Ga, 90Y, 99mTc, 111In, 131I and 177Lu nuclides in water solutions enclosed either in glass or in plastic receptacles, such as vials or syringes of different sizes and filling fractions. Superficial and deep dose equivalents were estimated, around the lateral surface of the receptacle, at different distances. A comparison was made with the results from VARSKIN 5.3, which were computed in the standard VARSKIN geometric lay-out of a volume source. Results Skin and deep dose equivalents, at 70 μm and 1 cm of depth, are reported for all the considered configurations, highlighting the importance of adopting a realistic geometrical configuration. The comparison made between the average exposition below the source bottom, computed through VARSKIN, and the maximum exposition on the lateral surface at the source middle plane, evaluated by Monte Carlo simulations, reveals a qualitative agreement for a limited number of configurations only, since the different geometries affect the dose deposited in the scoring volumes. A further source of disagreement is related to the deterministic approach in which electron energy deposition is treated in VARSKIN and its influence in proximity of electron maximum range, and to the absence of bremsstrahlung emission. Another source of discrepancy, for some nuclides, is the difference in radionuclide emission spectra. Conclusions Due to the easiness of implementation of GAMOS simulations, case-specific realistic geometries and nuclides can be adopted and results can be obtained in very reasonable computation times. [ABSTRACT FROM AUTHOR]

Twenty-two patients with suspected brucellar spondylitis were investigated to evaluate the possible diagnostic role of Sulesomab, a99mTc-antigranulocyte antibody Fab′ fragment. Sensitivity and specificity were compared with those of magnetic resonance imaging (MRI). Skeletal involvement was detected by MRI in 11 cases, while leukoscintigraphyindicated normal vertebral uptake in seven of these patients, increased uptake in two patients, and decreased uptake in two patients. Leukoscintigraphy of the 11 patients negative by MRI demonstrated increased uptake in two cases. The sensitivity and specificity of leukoscintigraphy were 27.2% and 81.1%, respectively. Based on these results, leukoscintigraphy is not indicated for the management of patients with suspected brucellar spondylitis. [ABSTRACT FROM AUTHOR]