ABSTRACT
The aim of this work was to establish how well gel dosimeters performed, as substitutes for brain tissue compared with standard phantom materials such as water, polymethyl-methacrylate [or PMMA], A150 plastic and TE- liquid phantom material for dosimetry of neutron beams in boron neutron capture therapy. Thermal neutron fluence, photon dose and epithermal neutron dose distributions were computed for the epithermal neutron beam of the optimized linac based BNCT. Amongst all investigated phantom materials, TE-liquid was shown to be a better substitute for brain tissue than other phantom materials. The differences between TE- liquid and brain at the depth of 6.1 cm for thermal neutron fluence, gamma dose and epithermal neutron dose distributions was calculated 2.80%, 2.40% and -13.87%, respectively. In comparison with the other gel dosimeters, LMD2 provided a better simulation of radiation transport in the brain. It's results differed from the real brain, at the depth of 6.1 cm, for thermal neutron fluence, gamma dose and epithermal neutron dose distributions, by -1.27%, 4.20% and 21.05% respectively. Even though, in gamma dose distribution the LMD2 has large deviation from brain tissue distribution, the deviation is approximately independent of depth, so the results can be multiplied by a constant coefficient to be more consistent with reality. Even though, TE- liquid showed satisfactory results for brain tissue substitution in BNCT, but some properties of gel dosimeters such as three dimensionality, make LMD2 a potentially good dosimeter for dosimetric verification in BNCT
Subject(s)
Radiometry , Gels , Phantoms, Imaging , Polymethyl MethacrylateABSTRACT
In addition to gas pollutants, many chemicals and air pollutants are in the form of particulate matter. Particulate matter consists of a complex mixture of variable sized particles and physicochemical composition. These particles mainly contain minerals including Fe, Al, Ca, K, Cu, Ti, Mn, Ni, V and their size, chemical composition and concentration are important to assess the extent to which people has been protected. Instrumental neutron activation analysis [INAA] was employed to determine the composition of elements in material collected on Whatman 41 filter using high volume air sampler in Rasht. Conce ntration of elements including Al, Ca, V, Mg, Cu, Ti, K, Ba, Cl, Mn, Na, As, Br, Cr, La, Sb, Co, Fe, Hg, Sc and Zn were determined in samples. Results showed that the levels of most air pollutants in Rasht to be lower than those measured in other cities in Iran [Tehran, Esfahan and Shiraz] by the same technique. Compared to other cities in world except for some elements, mean concentration of elements in air in Rasht were lower than those reported for Milan, Pavia and Beijing. Although the level of most air pollutants in Rasht are lower than those measured in other cities in Iran, due to considerable differences in element concentrations depending on the day of sample collection, more detailed studies are needed to control the emission of pollutants in this region
ABSTRACT
Sensitivity and resolution are two main parameters that have to be measured in gel dosimetry. However, the resolution in gel is strongly dependant on gel composition. Selection of optimum method in dose response readout and proper values of parameters can result in noise reduction as well as improvement of contrast, and spatial resolution considerably. MAGICA polymer gel dosimeters were manufactured and irradiated to different doses using a 60Co therapy unit. Imaging was performed in a 0.5T MRI with 8 echoes in air and water as a hydrogenous environment. Imaging condition was kept constant, as much as possible, in both imaging modalities. Images obtained from these two procedures were compared quantitatively. R2- dose curves have three different sections, sensitivity obtained in these three sections were 1.039, 1.671, 1.260 Gy[-1]S[-1] and 1.032, 1.729, 1.37 Gy[-1]S[-1] for water and air respectively. Calibration errors were investigated and graphically were compared in two different methods. Imaging in water medium for doses lower than 17 Gy led to a small reduction in spatial resolution was exchanged to a considerable increase of contrast in R2 map. For doses higher than17 Gy, imaging in water or air was preferred depending on the importance of contrast or spatial resolution