فهرست مطالب داریوش سرداری

Pancreatic cancer leaves little hope for survival among patients. This is due to its cancerous cell resistance to radiation and chemicals.

Synergistic effect between three modalities of pancreatic cancer treatment is investigated. These are radiation therapy, Hyperthermia and graphene oxide nanosheets. The aim is to overcome resistance of pancreatic cancer cell against radiation therapy.Cancerous cell lines were treated by each one of three modalities separately. Other samples were treated with various combinations of these modalities. Hyperthermia accomplished with placing cell lines for 15 min in 42°C. In the course of radiation therapy, the cancerous cells were irradiated by 6 MV Linac for two cases of 2 Gy and 3 Gy. The cell line viability was readout by MTT assay in 24 hours and 48 hours after treatment.

In single modality treatment it was shown that 24h after the treatment, the group treated by RT 3 Gy had the highest cell killing result. Following up the result in 48h readout, hyperthermia and 3 Gy radiotherapy had similar result. In double modality treatment, for both 24h and 48h viability readout, the group graphene -oxide plus 2 Gy radiotherapy showed cell survival amounting to 67.07% and 43.23% respectively being the lowest cell survival among all double combinations.

In triple modality treatment, the cell viability for 24h showed no significant improvement but in 48h the hyperthermia plus Graphene -oxide and 3 Gy radiotherapy had very low cell viability. Significant sensitizing effect for GO when combined by radiation therapy was observed.

High energy photons (10-20 MeV) that originate form medical linear accelerator in Radiotherapy treatment room, produce neutron. The produced neutrons id absorbed with different materials in the accelerator, the environment and even patient body that produced radioactive materials. These radioactive materials may pose a risk of radiation exposure to the radiotherapists who go to the treatment room frequently between patients. This process may cause internal radiation exposure in addition to external radiation exposure.  In this research after the expose of 18 MV X-Ray by medical accelerator (Varian 2300C/D), the spectrum of accelerator head was collected by portable HPGe detector and 19 radioisotopes were recognized.

This research uses the portable HPGe and NaI(Tl) detectors for Compton continuum suppression.In the List mode data acquisition technique, we did not use timing module and complicated experimental setup that recorded the time stamp of each event. The maximum suppression factor (SF) in Cs-137 point source was 3.8. By using this technique, we can detect samples that contain very low radioactivity. The experimental setup in this research was based on analog nuclear electronic modules. The study's main goal was the ability of list-mode data acquisition in Compton continuum suppression. In this way, lower levels of radioactivity can be detected in any sample.

In this study, Lithium Fluoride nanopowder with Mangnesium and Titanium impurities has been synthesized by Co-precipitation method. The synthesized powder was then pressed into 3.2*3.2*0.9 mm3 pills and sintered at 750⁰c for 10 minutes.  The peak 5 in LiF: Mg, Ti is regarded as the main peak and includes sub-peaks 5a and 5b, which occur at the temperatures lower and higher than that of peak 5, respectively. Peak 5a in LiF;Mg,Ti occurs due to the localized recombination of trapping/luminescence center (TC/LC) , in which the electron is released from the electron trap by obtaining energy from heat and recombines through the tunneling phenomenon with a hole located in the adjacent luminescence center. Concerning the standard TLD chips, which are composed of micron-sized particles, the peak 5a either does not occur or appears with very low intensity, which is insignificant in terms of dosimetry. Thus, the present study focuses on synthesizing thermoluminescence nanoparticles by co-precipitation method in several stages by citing models based on the maintenance of linear behavior of thermoluminescence nanopowder up to high doses and its relationship with localized electron-hole recombination. In addition, by making changes in the concentration of ingredients, the temperature of the reaction medium and the presence or absence of surfactant were evaluated to achieve particles in nano dimensions with suitable geometric shapes. The resulting nanopowder was irradiated with different doses of alpha and gamma and consequently, the increasing rate of the intensity of peak 5a compared to peak 5, as the main factor in nanodosimetry was observed after analyzing the glow curves. Based on the results, the LiF: Mg, Ti thermoluminescence nanopowder could increase the 5a/5 ratio and can be used as a convenient, inexpensive, and practical tool to estimate the amount of energy deposited by the beams in nanoscale.

Radiation therapy is one of the most effective methods in the treatment of cancer. The use of protons and light ions in radiation therapy is developing due to the different physical interactions with the photons and the application of concentrated doses in the Bragg region. However, new methods to increase the efficiency of treatment have always been considered. One is addition of nanoparticles of high-Z materials to the tissue, which while increasing the effective atomic number of the tissue, increases the effective dose during radiation therapy and causes more damage to the DNA. In this study, using the Geant4-DNA toolkit, we defined B-DNA as PDB format in the geometry. DNA damages after proton interactions in the energy range of 0.1 to 20 MeV were calculated. The number and efficiency of single-strand breaks (SSB) and double-strand breaks (DSB) have been calculated by considering direct and indirect interactions with / without the presence of nanoparticles. By comparison, it was found that the obtained results without nanoparticles are well consistent with previous studies. The results of this study show an increase of up to 15% for single-strand damage and up to 80% for double-strand breaks in the presence of gold nanoparticles. Also, the amount of DNA damage in the presence of iodine and gadolinium nanoparticles was reduced by 7% and 13% compared to gold, respectively. The results of this study show that nanoparticles can be used to improve the effectiveness of radiation therapy.

In this research, air samples were collected at an air flow rate of 300 m3/h to 900 m3/h. These samples were collected during more than two months (Nov 2019-Jan 2020). After the decay of short-lived radionuclides, the samples were formed as a disc to prepare for measurement. Then, these discs were evaluated by two HPGe detectors with relative efficiencies of 40% and 70%. A prototype of a standard high volume air filter was proposed and constructed by a novel method, which provides a symmetric distribution of radionuclides and efficiency calibration curve was obtained for two HPGe detectors. This standard filter was solved the problem of the asymmetry and inhomogeneous distribution of radionuclides in standard air samples. 7Be concentrations were assessed in the collected samples. The average concentration of 7Be was measured as 3.80±0.46 mBq/m3.

The origins of radon gas are the amount of uranium decay in the soil that is released into space and through the interior gaps of  buildings. Radon can enter the respiratory system and cause radiation hazards. Recently research has identified Radon as the second leading cause of lung cancer after cigarette smoking. The indoor concentration of Radon progeny is mentioned as an important issue regard to the point of view of health. Therefore, a more accurate measurement of the concentration of radon gas in order to assess the exposure of people is of great importance. The purpose of this research  is to measure radon gas with two contemporary and retrospective methods in Ramsar homes, which is known as a high level background radiation area, as well as comparison with previous measurements. In order to measure the Concentration of contemporary radon by  passive method using a radon chamber and solid state nuclear track detectors, a retrospective of the activity of polonium 210 implanted in glass objects was used to measure the concentration of radon gas. The solid state nuclear track detectors used in this research are polycarbonate, which is the first time used in this world for this type of polymer for the retrospective method. The average concentration of measured for contemperory radon is about 416 Bq /m3 and the resrospective radon is about 1299 Bq /m3. According to the comparison of the results  with the US Environmental Protection Agency standards, it was found that 45% of the radon gas concentration is above 148 becquerel per cubic meter, which is indispensable for reducing radon gas in these buildings. At the same time, the difference in the concentration of rare earth radiant gas with contemporary radon gas can be related to the change in the ventilation rate and the change in the concentration of aerosols and the ratio of the surface to the volume of the room.

The application of large plastic scintillators is widely increasing in the different areas of industry, medicine and security due to technical and economic advantages. One of the main disadvantages of these detectors is the unknown position of Compton edge at gamma ray spectrum. In this research, GEANT4/GATE code has been used to simulate the gamma ray spectrum for different volumes of large plastic scintillator. According to these simulations, the dependence of the Compton edge position, energy resolution at Compton edge and efficiency of the optical photon collection to the scintillator dimensions has been investigated. The simulations showed that the Compton edge position with respect to local maximum at Compton continues strongly depends on the scintillator dimensions. These results were verified by experimental spectrometry.

 In this research, we examined the different mathematical models of cancerous tumor growth and compared several models to calculate and evaluate the response of the growth logistic model to the specific growth rate conditions. The growth rate was simulated by considering it as a function of time (linear, exponential growth, and linear growth-decay). Responses were obtained by using Range-Kutta's numerical solution method. The general response is the logistic growth curve, but the external factors in the treatment can be controlled to optimally respond of model.The optimal conditions for controlling the growth of the tumor obtained by the linear growth rate-decay for the constants k1=0.1 and k2=1. Solid tumor structure is associated with a decrease in the stage of growth of the cells prior to angiogenesis. Increasing lagging agents such as accelerating immunological response during exponential growth functions can control tumor growth. The numerical results obtained in this study can provide an optimal therapeutic strategy by reducing the volume of primary cancer by calculating angiogenic inhibitors. Also, by analyzing pathology, mechanical properties of tumor growth, cellular adaptation and therapeutic resistance, we can overcome some of the previous constraints in the general growth model.
Key Words: Treatment, Tumor growth, Cancer, logistic mathematical models, Control

Employing High-energy photons in medical linear accelerators can lead to neutron contamination. The relative biological effect of neutrons is 20 times higher than photons. Consequently, its damage to the biological tissue is much higher and unobtrusive. In this study, we calculated neutron equivalent dose in a medical linear accelerator by the FLUKA Monte Carlo code system. The results show that using smaller treatment fields increases the neutron contamination dose in out-of-field areas. Furthermore, the areas outside the treatment field receive several times higher neutron dose than the photon dose. Most of the neutron dose distribution is at the surface of the human body. So it could increase the secondary cancer risk, including skin cancer.

Reduction of background track in solid state nuclear track detectors is an important topic in dosimetry. The main objective of this research is to optimize the reduction of background track using the chemical pre-etching process for removal of surface layer of the detector followed by electrochemical etching process. In this regard, the chemical reaction between a polycarbonate detector and ethylenediamine solution with various density portion of 20%, 30%, 40%, and 50% is studied. Accordingly, some empirical relationships between removed layer thickness and etching time in different solution density are derived. The results of experiments illustrate that best outcome in the uniformity of etching can be achieved at density of 40% with 50% of background track reduction.

Microbeam radiation therapy (MRT) is an innovative experimental method used for radioresistant tumours such as glioma especially in pediatric cancer. In MRT, the patient is irradiated with arrays of parallel and high-intensity X-ray microbeams. The MRT offers dose profiles consisting of a pattern of peaks and valleys. The peak-to-valley dose ratio (PVDR) is the most important metric determining the effectiveness of MRT. Its value has to be maximized in normal tissue, and minimized in cancerous tissue in order to avoid any recovery. The main aim of this study is to investigate the possible effect of beam parameters on PVDR. To do so, the 3D dose distributions in water and head equivalent phantoms are computed with various microbeam configurations using GEANT4 simulation. The results show that the most promising PVDR are obtained at 100keV and ESRF spectrum. In addition, using a 300keV beam is not suitable for microbeams separation distance below 400μm. By increasing radiation field size, microbeam’s width and their separation, PVDR decreases for all energies. PVDRs in the bone rapidly fall because of the dominant photoelectric phenomenon for such a high-Z material.

Particles or ray detectors are devices with which detect, trace or distinguish high energy particles. One of these detectors is Gallium arsenide (GaAs). Difficulties in producing consistently the thick layers with sufficiently low doping required for adequate depletion depth (>100 µm), however, precluded further development. Then, there has been renewed interest in detectors based on both bulk- and epitaxially- grown materials. Hence, aim of this study was studying characterization, application, advantages and disadvantages of Gallium arsenide (GaAs). Defects of GaAs can be classified under geometrical aspects (dimensionality) or under the aspect of their origin (intrinsic and extrinsic defects). When GaAs uses as X ray detector, absorption character, resistivity, mobility and lifetime, material uniformity used in detector, performance stability and processibility should be consider. Types of imaging detectors GaAs are detectors based on epitaxial GaAs, detectors based on (compensated) SI-GaAs, detectors based on Cr-compensated HR-GaAs. A good spectroscopic performance, high CCE values and good image quality can be achieved with detectors based on epitaxial GaAs. The material homogeneity was reported to be higher and local variations of material properties to be less pronounced than in bulk material. In addition, advances in flip-chip processing techniques for high-Z compound semiconductors give reason for hope for high pixel yields and thus good image quality.

Given the importance of CT imaging in the diagnosis and treatment of diseases, the concern of the dose that patients are receiving while undergoing CT examination and the lack of information about the situation in the centers CT scan was conducted at Shahid Beheshti University of Medical Sciences. A descriptive study was conducted. A list of CT scans of patients who are still under the supervision of Shahid Beheshti University of Medical Sciences were prepared (the public sector). Exposure data were collected via referring to the centers (kV voltage level and mA and scan time) and two methods were used and back up CT scan of the patient's history was carried. Dosimetry on phantoms, phantom head and body with the same exposure conditions (radiation) was performed and the organ dose and effective dose received by mili Gary was calculated according mili Sivert. The research was conducted in five centers with CT scan. In CT scan of the head (head CT) brain dose, the highest dose (31.55 mG) and bladder lowest dose (zero) and in CT scan of the chest (chest CT), breast highest dose (20.67 mG) and bladder lowest dose (0.005 mG) and in CT scan of the abdomen and pelvis (abdominal pelvis) bladder highest dose (16.44 mG) and brain lowest dose (0.002 mG) was calculated. Furthermore, effective dose received by patients for three protocols of the head, chest, abdomen pelvis centers surveyed, respectively. The lowest effective dose for the patient CT scan of the head (0.16 ± 1.55 mSv) and the lowest effective dose for the patient CT scan of the chest (0.3 ± 3.4 mSv) and the highest effective dose received by patients CT scan of the abdomen pelvis (0.3 ± 6.8 mSv), respectively. It seems organ dose and effective dose in some higher centers of the world standard (ICRP) and the overall dose exposure is a concern.

In this study, the pure nano-structure hydroxyl apatite samples were synthesized via hydrolysis method. The powder samples were sintered at various temperatures of 500°C, 700°C and 900°C in a furnace. X-ray diffraction (XRD) and Fourier transform infra-red (FTIR) spectroscopy systems were used to characterize the synthsized samples. Comparison of the glow curves shows that the most sensitivity and highest thermoluminescence (TL) intensity is belong to the samples sintered at 900°C. Dose response curve of the samples is linear in the dose range of 25Gy-1kGy. Other dosimetry characteristics such as dose-response function, fading, and reproducibility of the TL response were also studied. In order to eliminate the error originating due to fading effect, an annealing process was applied on the samples. The results shows that the sintered nano-structure hydroxyl apatite sample can be used for dosimetry in gamma radiation fields.

SPECT is a diagnostic imaging technique the main disadvantage of which is the existence of Poisson noise. So far, different methods have been used by scientists to improve SPECT images. The Wavelet Transform is a new method for de-noising which is widely used for noise reduction and quality enhancement of images. The purpose of this paper is evaluation of noise reduction in SPECT images by wavelet. To calculate and simulate noise in images, it is common in nuclear medicine to use Monte Carlo techniques. The SIMIND software was used to simulate SPECT images in this research. The simulated and real images formed using the current typical (hexagonal) collimator were de-noised by different types of wavelets. The best type of wavelet was selected for SPECT images. The results demonstrated that the best type of wavelet in the simulated and real images increased Signal to Noise Ratio (SNR) by 33% and 45% respectively. Also, Coefficient of Variation (CV) decreased by 77% and 71% respectively, while Contrast of Recovery (CR) was reduced by only 4% and 9% respectively. Comparing the results for real SPECT images in this paper with previously acquired results in real PET images, it can be concluded that the images of both nuclear medicine systems using Wavelet Transform differ in SNR and CR by only 5% and 7% respectively, and in CV by about 20%. Therefore, wavelet transform is applicable for nuclear medicine image de-noising.