فهرست مطالب a. haghparast

Nucleic acid aptamers have been emerged as potential molecules for target-specific drug delivery because of their ability to bind targets with very high affinity and specificity. Rapid renal clearance is one of the major issues associated with the vascular delivery of nucleic acid-based drugs. To circumvent this problem, this study was designed to envision the development of nucleic acid aptamers specific to human erythrocyte as erythrocytes travel through the cardiovascular system. Erythrocytes have special properties which make them peculiar and specific as a physiological carrier for drug delivery For this purpose, we have performed Cell-SELEX procedure using human erythrocytes containing 4-O-((2-O-(β-D-fucopyranosyl)-3-O-(α-D-galactopyranosyl))-β-galactopyranosyl)-2-acetamido-2-deoxy-α-D-glucopyranoside on the surface as a model target. After completing 15 rounds of selection, sequencing of the product identified RNV543 and RNV544 as potential oligonucleotides specific to the target human erythrocyte. The binding affinity of both RNV543 and RNV544 was confirmed by flowcytometry. This study showed there is Aptamers which can have specific binding to erythrocyte type B.

Head and neck cancers are currently the most common types of cancers. 3D-conformal radiation therapy is the most common dose delivery technique for head and neck cancers. Eye Lens is a radio sensitive structure and cataract formation as a visual disorder associated with exposure to ionizing radiation which is documented.

Determining the radiation dose to eye lens during head and neck radiography and estimating the probability of cataract induction are essential.

This experimental study was performed on 14 patients with head and neck cancers through experimental study analysis. The maximum opacity of the eyes lens were measured by pentacamTM before radiation therapy. CT data of patients were transmitted to Isogray treatment planning Software, and dose calculations for each patient was performed. At the end of radiation treatment, 3 and 6 months after radiotherapy, the eye lens opacity of the patients was assessed.

Overall, 28 lenses were studied. Statistical one sample K- S test proved normality of obtained data. Using repeated measures test, the relation before and 3 months after radiotherapy, as well as the relationship before and 6 months after radiotherapy proved a significant relationship.

The opacity caused by radiation in eyes is a non-statistical and linear-quadratic response curve with no threshold. This opacity can also appear within 3 months after completion of radiation therapy.

Intensity Modulated Radiation Therapy (IMRT) is extensively used in the treatment of malignancies. Clarkson’s method is one of the leading methods for dose calculation at open points present in irregular fields. The aim of this study is to generalize the Clarkson’s method for dose calculation at points under compensator filters in IMRT method and its application in IMRT quality control as well. In this experimental study, compensator filters were designed in two forms: flat filter and block piled-up compensator. The measurements for the compensator filters and open fields in 5 and10 cm depths at energy levels (6, 10 and 18 MV) and in fields with different dimensions were performed using “Mapcheck2” dosimeter. The aim of performing calculations is to derive the theoretical dose by the generalized Clarkson’s equation and comparing it with data resulted from the measurement for confirming the Clarkson’s equation presented. These results demonstrate the data derived from the generalized Clarkson’s method are in good agreement with the data resulted from measurement; the highest error of the proposed equation was 3% for flat filter, and less than 5% for block-piled-up filter. Higher error in the block-piled-up filter compared with the flat filter was due to the presence of leakage between these blocks. The results of this study demonstrated that the presented equation is reliable and valid, and the proposed equation can be applied for dose calculation at all points under the compensator filter or the shielded areas.

131I source is widely used in the treatment of hyperthyroidism and thyroid cancers. 131I emits both beta and gamma-rays. Radiation protection is considered for gamma rays emitted by 131I. It seems no special shield against 131I source to be designed. This research aims to evaluate determination of optimum shields in nuclear medicine against 99Tcm and 131I sources by dosimetric method. Additionally, Monte Carlo simulation was used to find the optimum thickness of lead for protection against 131I source. This is an experimental research in the field of radiation protection. A calibrated model of GraetzX5C Plus dosimeter was used to measure exposure rates passing through the shields. The efficiency of the shields was evaluated against 99Tcm and 131I. Furthermore, Monte Carlo simulation was used to find the optimum thickness of lead for protection against 131I source. The findings of the dosimetric method show that the minimum and maximum efficiencies obtained by the lead apron with lead equivalent thickness of 0.25 mm and the syringe holder shields with thickness of 0.5 mm lead were 50.86% and 99.50%, respectively. The results of the simulations show that the minimum and maximum efficiencies obtained by lead thicknesses of 1 mm and 43 mm were 19.36% and 99.79%, respectively. The optimum shields against 99Tcm are the syringe holder shield, the tungsten syringe shield, and the lead partition, respectively. Furthermore, based on simulations, the thicknesses of 11-28 mm of lead with efficiencies between 90.6% to 99% are suggested as the optimum thicknesses to protect against 131I source.

Small field dosimetric challenges lead to a deviation from the reference dosimetry. The aim of this study is to investigate the changes of polarization (kpol) and ion recombination (ks) correction factors and determination of leakage dose in small fields.

All values were measured on a RW3 slab phantom, at 100 cm Source-to-Surface Distance, 10 cm depth and 6, 10 and 18 MV photon beams for square fields (0.5 to 10 cm). Three ionization chambers (PTW Pinpoint 31014 and 31015, Semiflex 31010) were hired. After the electrometer readout, the correction factors were computed according to the protocol No. 398 of International Atomic Energy Agency's Technical Report (IAEA TRS-398).

The kpol (min) and the kpol (max) value occurred in 0.5×0.5 cm2 and 10×10 cm2 field size, respectively. Dosimeters with a larger sensitive volume showed greater kpol values. In all three dosimeters, an increasing trend detected in normalized dosimeter reading after working voltage. The level of leakage in all of the values and radiation conditions was at the level of a few Nano colons.

The values of kpol and ks in the small fields were different from the reference field. The saturation voltage of the small field dosimeters was greater than the dosimeter working voltage. The leakage values of the dosimeter-electrometer combination in the present study were negligible for all radiation conditions. The correction factors should be considered due to the differences between small fields and reference dosimetric conditions.

In this paper, we used a coherent beam combination to design a 50 kW high power laser beam for energy applications. Because of the strong environmental turbulence, degrade the coherent beam combination advantages, low turbulence level is considered. Combining elements are composed of 19 polarized single mode 3 kW high power fiber lasers where are arranged in the co- two centric hexagonal rings. Each of the fiber a lasers has a collimator with a 30 mm beam spot size output. We extended the transmitting range to z=10 km and the improved filling factor up to f=0.91. Therefore, power loss at the side lobes are minimized and resulted in the rise of combination efficiency to 88%, which is the highest published result. The central spot size radius on the target is R=5.9 cm, where indicate 0.45 kW/cm2 power density. Also, the effect of Phase errors of the combining elements at the far- field, which cause the ray intensity scattering from the center spot to the side lobes is investigated.