alireza sadremomtaz

Quantitative accuracy in SPECT is mainly affected by collimator penetration and scattering, particularly for high-energy imaging. Lofthole collimation offers superior performance in terms of penetration and scattering. In this research, the GATE Monte Carlo simulator was exploited to calculate edge penetration and scattering in the lofthole collimator using an in-air and in-phantom point source of Tc-99m and I-123. The performance of the lofthole was then compared to that of a pinhole. Both lofthole and pinhole collimators were assumed to have the same geometry including an aperture diameter of 3.04 mm and an opening angle of 75°. Furthermore, the angular distribution of the scattering and penetration were investigated for a multi-lofthole collimator. The results show that penetration, scattering, and sensitivity are all a function of the photon energy. The penetration and scattering of the pinhole are about 4% higher than that of the lofthole collimator, for Tc-99m SPECT. Compared to the Tc-99m, I-123 SPECT suffers from approximately 1.5- and 1.42-fold higher penetration and scatter fractions, respectively, for lofthole aperture. Moreover, the lofthole collimator presents a higher sensitivity compared with the pinhole (0.030 versus 0.023 for the Tc-99m SPECT). In addition, the findings exhibit a reduction in sensitivity by increasing the photon incidence angle. Both scattering and penetration fractions illustrate a decreasing trend across the angle of incidence. Compared to pinhole, the lofthole offers superior performance in terms of scattering and penetration for both low- and high-energy SPECT imaging.

Dose evaluation is one of the main steps in cancer treatment. In process of treatment it is always a concern to conentrate the absorbed dose on the effected area and reduce the abosorbed dose on healthy organs. Brachytherapy is One of the major cancer treatment methods which uses various radionucleids as source. Although the most common source in this method is Ir-192 but Cs-137 has also an extensive use too. In this study the Absorbed dose in the superficial brachytherapy for treatment of keloids has been evaluated.    Cs-137 was chosen as source and  MCNP4C code was employed for the simulation.

the absorbed dose due to ionizing radiation is a function of three parameters: 1- Time 2- Source 3- Shielding. shielding materials -as any other material- activate when they are exposed to irradiation. The aim of this study is to calculate the attenuation coefficient and investigate shielding properties of different concrete compounds with various aggregates. After that the required time for achieving IAEA anounced clearance levels for these compounds was calculated by ORIGEN-S code.Cs, Co and Eu are important radionucleids in term of determine the required time for achieving clearance levels.

The Tc-99m DMSA is one of the most widely used radiopharmaceuticals in nuclear medicine. This radiopharmaceutical is used to study the location, size, shape, and function of the kidneys. In this paper, the absorbed doses of different organs and the effective dose after injection of this radiopharmaceutical have been calculated using the MIRD method. For this purpose, the specific absorbed fractions have been obtained for adult phantom of revised ORNL phantom series using Monte Carlo simulations, and then the S values ​​for the Tc-99m radionuclide have been calculated. Finally, the absorbed doses of different organs have been calculated using the biokinetic data of ICRP 53 for Tc-99m DMSA. The results show that the kidneys, bladder wall, spleen, and adrenal glands receive the highest absorbed dose after injection of Tc-99m DMSA. Also, the effective dose per unit activity administered is estimated to be 1.60E-02 mSv/MBq.

Cis-4-[18F]fluoro-L-proline is one of the 18F-labelled amino acids which can be used as a tracer to identify abnormal collagen synthesis rates. This study aims to estimate the absorbed and effective dose of this radiopharmaceutical using ICRP reference phantoms and the ICRP 103 tissue weight factors, which have not been done so far. For this purpose, the MIRD method was used to estimate the absorbed dose of organs. The data relating to the distribution of this radiopharmaceutical in the body were taken from a previously published study. Also, the absorbed dose and effective doses were calculated for revised ORNL phantoms to validate and compare the results. The effective dose coefficient of this radiopharmaceutical using the tissue weighting factors of ICRP 103 is 1.52E-02 mSv/MBq. The kidneys receive the highest absorbed dose after the injection of this radiopharmaceutical. For a given administered activity, this radiopharmaceutical leads to a lower effective dose to the patients than FDG.

Internal radiation dosimetry is important from a radiation protection point of view and can help to optimize the radiation dose delivered to the workers, public, and patients. It has a rather simple protocol but needs a large amount of data. Therefore, it is difficult to do on a routine basis. The use of computer programs makes internal radiation dosimetry simpler and less time consuming and also decreases the possibility of human errors. The photon’s specific absorbed fractions for two versions of Oak Ridge National Laboratory phantoms were calculated using MCNPX code and a Python code was used to calculate the S-values for selected radionuclides. Then calculated S-values transferred to an excel spreadsheet. The program’s GUI was developed with the Tkinter module of Python programming language. A user-friendly program for internal radiation dosimetry was developed using Python programming language. This program allows the user to calculate the absorbed dose for 20 source organs in 23 target organs for two phantoms. Also, it is possible to compare the results of the two phantoms. Originally, 40 radionuclides were included in the program. This program can be a useful tool for the assessment of organ absorbed doses for individuals dealing with radiation such as patients and workers. It decreases the time of dose calculation and helps to avoid human mistakes.

Thyroid scanning is performed to examine the thyroid gland disorders using 99mTc. Through the obtained images can evaluate the size of the thyroid gland, the amount of its removal compared with the salivary gland, examine the thyroid nodules and its performance impairments. According to the scan view, it is possible to differentiate between hot and cold thyroid nodules that need different therapies. The study of cervical mass with expansion to the chest is another major function of thyroid scanning with 131I. In this method, 24 hours after administration of little 131I, imaging of the neck and chest area is performed. The purpose of the present study was to simulate the emitted particles of 131I radiation and 99mTc, calculate and compare the absorbed dose and the S-value of these two radiopharmaceuticals in the thyroid and other organs around the thyroid, such as the lung, skin, and brain. Simulation and computations were performed using the Monte Carlo method by MCNPX software. ORNL MIRD phantom geometry was used for thyroid and other organs geometry. The absorbed dose in the thyroid and other organs increased with increasing activity, but the absorbed dose in the other organs was lower than the thyroid. The results showed that absorbed dose in 99mTc was lower than 131I. Although  131I has a diagnostic function in thyroid diseases, it has its own special disadvantages. 131 I in addition to 364kev high energy of gamma photons radiations, emits high-energy particles of 647 kev beta, too. Secondly, it has a lifetime of 8/05. Therefore, in studies conducted with 131I, the amount of radiation exposure of the thyroid gland and the total body  is very high (about 15,000 rades are the absorbed thyroid dose). On the other hand, the Tc pertechnetate with a lifetime of 6 hours and gamma energy of 140 kilos of electron volts, like 131I, is absorbed by the thyroid gland. Therefore, regarding the advantages of Tc pertechnetate to the 131I radiopharmaceutical , it is possible to use the absorbing of Tc  pertechnetate  as a measure to evaluate thyroid function.

Neutrons have many applications in various fields, such as industry and medicine. In nuclear facilities, and especially in electricity production, we are faced with such radiation. Because of this, determination of neutron dose is critical for the health of workers and patients exposed to this beam. The neutron radioisotope sources produce gamma rays in addition to the neutron, and the neutron fields around these sources are mixed-field neutron-gamma fields. Different methods of dosimetry of the neutron field include the method of gold foil activation and the method of using a thermoluminescence dosimeter pair. One of the effective ways of neutron dosimetry is the use of the TLD-600/700 thermoluminescence dosimeter pair. The TLD-600 is sensitive to thermal neutrons due to the richness of 6Li (which has a high thermal neutron absorption cross section) but the TLD-700 does not have thermal neutron sensitivity in low fluxes. In this paper, to measure the neutron dose from the Ra-Be neutron source in the core laboratory of the Faculty of Science of the University of Guilan, six TLD-600/700 dosimeters were used in three intervals of 7, 14 and 20 cm from the source. Finally, by calculating the neutron dose through the source flux and estimating the calibration coefficient, the dose rate measured by the TLDs was determined and compared with the calculated dose rate.

The use of beta emitters is one of the effective methods for palliation of bone metastasis. The risk of normal tissue toxicity should be evaluated in the bone pain palliation treatment.
In this study, the Monte Carlo simulation code MCNPX was used for simulation a bone phantom model consisted of bone marrow, bone and soft tissue. Specific absorbed fractions were calculated for monoenergetic electrons, photons and eight betaemitters: 32P, 89Sr, 90Y, 153Sm, 166Ho, 177Lu, 186Re and 188Re. Beta and gamma S-factor, absorbed dose and cumulative dose of mentioned radionuclides were obtained to the selection of radionuclides with optimal radiation characteristics.
The results show 177Lu gives a higher local dose to source organ. 177Lu has fewer side effects on critical organ including bone marrow in comparison with other radionuclides such as 89Sr, 32P and 90Y. Cumulative dose versus time shows after a long time, long half-life radionuclides delivering a higher dose in comparison with the short-half radionuclides.
According to the results, low energy β-emitters177Lu, 153Sm and 186Re can be used for bone pain palliation especially in vertebra. Different combination of these radionuclides can be used to improving therapeutic effects for tumors with different size.

Image quality and accuracy of in vivo activity quantification in SPECT are affected by collimator penetration and scatter components, especially in high energy imaging. These phenomena highly depend on the collimator characteristic and photon energy. The presence of penetrated and scattered photons from collimator in SPECT images degrades spatial resolution, contrast and image quality. Knowledge of penetration and scatter distribution is essential for optimization of collimator design and development of reconstruction algorithms.The aim of this study to survey the collimator performance of the newly developed HiReSPECT dual head gamma camera with pixelated array CsI(Na).
We modeled the HiReSPECT, by using SIMIND Monte Carlo simulation code. The contribution of geometric, scatter and penetration components were quantitatively calculated for the different energy sources. Then we compared these results with simulation results of another small animal SPECT with compact pixelated array CsI(Tl) detector.
The simulated System spatial resolution and energy resolution of the HiReSPECT at 140keV respectively are 1.9mm and 29.72 keV (21.23%) FWHM at 2.5cm distance from detector surface also Geometric, penetration, and scatter at 140keV for the HiReSPECT collimator are 96.42%, 2.22%, 1.30%, respectively. Similarly, geometric, penetration, and scatter at 159keV and 245keV for this system collimator are (95.24%, 3.08%, 1.68%) and (87.21%, 8.10%, 4.69%), respectively.
The results verified that the magnitude of these components depend on collimator geometric structure and photons energy. The measured performances indicated that the HiReSPECT scanner is well suited for preclinical molecular imaging research and provide high resolution for small animal imaging.

The diagnostic accuracy of single photon emission computed tomography (SPECT) is profoundly influenced by attenuation phenomenon. Soft tissue attenuation degrades cardiac SPECT image quality, thereby decreasing the possibility of the detection of the lesions. A variety of correction techniques based on different assumptions have been used to reduce the impact of attenuation. Several types of systems with different transmission hardware modifications and external sources have been developed for clinical implementation. Each system has unique advantages and limitations. In this study, firstly, we introduce the attenuation phenomenon, the problems arising from it and the attenuation correction methods with description of the assumptions related to each of them. The main purpose of this study is to review the developments in the field involving various configurations used for attenuation correction of SPECT images, as tested using either phantom or clinical data, and to delineate an optimal attenuation correction technique by considering the advantages and limitations with each of the configurations.