نشریه سنجش و ایمنی پرتو
سال نهم شماره 2 (پیاپی 37، بهار 1400)

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.

During the proton therapy process, secondary neutrons are produced by the nuclear interactions of protons with the materials in the beam transmission line. In this study, the dose due to the secondary neutrons produced in an RW3 phantom was estimated using Monte Carlo simulation and was compared with the measured values. To do this, the neutron dose due to the collision of proton beams with energies of 100, 150, 200 and 220 MeV with the phantom, was investigated by Bonner sphere detectors and a tissue-equivalent proportional counter for different positions around the phantom vs. proton energy, length spread-out Bragg peak and the dimensions of the treatment field. With increasing energy from 100 to 220 MeV, depending on the position of the detector around the phantom, the dose due to neutron was increased up to 40 times. The effect of increasing the field dimensions from 2×2 to 20×20 cm leads to increase the induced dose up to 40 times for a specific energy. Also, with increasing the length of the spread-out Bragg peak up to 5 cm, a sharp increase in the dose was observed; after 5 cm, the increasing trend stopped and the dose amount did not affect the increase in the length of the Bragg peak spread area.

In order to investigate the effect of impurities on the dosimetric behavior of potassium chloride single crystals, KCl single crystals were grown without impurity and with impurities of Li, Ti, and Ca by Czochralski method. Pieces prepared from above crystals were irradiated at room temperature under gamma ionizing radiation at different doses. At the dose of 15 kGy, spot defects (color centers) created by absorption spectroscopy were investigated. In this study, in addition to the absorption bands F and Vk, which are specific to the KCl network, a small band was observed in the ultraviolet region, which resulted in the detection of Li impurities. The other effect of Li appears to be at lower energies with the deformation of the F band. The impurities of Ti and Ca were also observed in the form of increased optical stability and increased sensitivity of absorption curve measurements, respectively. In the study of luminosity curves in measuring the thermoluminescence (TL) spectra of the above crystalline samples that were measured after receiving gamma ray at a dose of 30 Gy, the effect of Li as the center of electron trap, Ti for increasing the depth of trap and Ca as the center of trap were identified. The Z1 electron appears in the formation of dipole (Vc - Ca2+) and thus allows further study of the dosimetry phenomenon in this environment.

The aim of radiation therapy is to maximize the dose applied to the tumor while minimizing the dose in adjacent healthy tissues. A new approach to meet this requirement is using high atomic number materials to label the tumor site. In this study, gadolinium was used for this purpose. In the practical part of the research, the 6 MV gamma source of linear electron accelerator located in Milad Hospital of Isfahan and a cubic phantom containing water were used. The detector area, which houses gafchromic films, is a rectangular cube, which is the hypothetical location of the tumor and healthy tissues on either side of it and is located inside the phantom. Different concentrations of gadolinium were injected into the tumor area and the dose enhancement factor (DEF) was investigated in different areas of the detector. The phantom and detector were simulated using the Geant4 software package. The dose enhancement factors were calculated in different regions of the detector and for different concentrations of gadolinium irradiated with low energy X-rays, 2 MeV gamma rays (mean energy of linear electron accelerator) and the photon energy spectra of 6 MV linear. Study shows that the dose enhancement factor increases with increasing gadolinium concentration. The optimum energy for DEF at all concentrations of gadolinium is about 70 keV, and its effect decreases as the energy of the photon increases. In the energy spectrum of 6 MV we see fluctuations in the amount of DEF for different concentrations of gadolinium due to the presence of low and high energy spectra of photons.

Careful treatment planning of brachytherapy is an essential aspect of cancer treatment. The aim of this study was to evaluate the accuracy of calculations of treatment design system in GYN brachytherapy by BEBIG-60Co device by performing entrance skin dosimetry (ESD) using TLD dosimeters. For this study, 11 GYN cancer patients selected for brachytherapy to measure skin surface dosimetry. Finally, a comparison was made between the dose calculation from the treatment design system and the dose measured by the TLDs. In about 90% of the cases, there was a good agreement between the treatment dose calculation and the TLD measurement (taking into account the 5.5% uncertainty for the TLD). Increasing the dose in the anterior position of patients 5 and 11 can be due to the displacement of the applicator in the direction of length. For patient No. 8, moving the Ooid applicator to the right has led to an increase in dose and a decrease in the right and left directions. Several factors, such as the movement of markers on the patient's skin and the movement of applicators during patient transfer between imaging and treatment rooms, cause differences in the dose of TLDs compared to the dose of TPS. Therefore, the method of dosimetry of the skin surface can be a suitable method to confirm the accuracy of the dose in the treatment of GYN HDR.

In this study, calcium sulfate nanoparticles doped with different percentages of ytterbium impurities were synthesized using the co-precipitation method. The structural properties and morphology of the nanoparticles were investigated by scanning electron microscopy (SEM) images and X-ray diffraction (XRD) patterns. Using the Williamson-Hall method an approximate size of 36 nm was obtained for the nanocrystallites. The results showed that nanoparticles synthesized with the presence of surfactant have a homogeneous and almost spherical structure. Also, the thermoluminescence glow curve following gamma irradiation and the photoluminescence spectrum of the samples were studied. The emission peak of photoluminescence at wavelength 1070 nm can be attributed to 2F5/2 to 2F7/2 transition. In addition, the results show that the nanoparticles synthesized in this method are sensitive to gamma rays at high doses and show a linear response in the range of 10 Gy up to 104 Gy. The fading of the samples during one month was about %10.

In this paper, a novel dual-band bandpass filter for the measurement and optimization of Wi-Fi waves exposure in the non-ionizing frequency range of 2.4 and 5 gigahertz, has been designed and simulated. In the novel proposed method for detection, initially the Wi-Fi waves have been filtered and then converted to the direct current signal in the detector. This filter consists of a complementary split ring resonator metamaterial and an interdigital capacitor which has been printed on a 50 ohms coplanar waveguide with the Rogers 3003 dielectric. In the equivalent circuit model of the bandpass filter, the complementary split ring resonator has been represented by a tank circuit which is in parallel with the coplanar waveguide. The interdigital coupling capacitor is in series with the waveguide. By adjusting the complementary split ring resonator radius and the interdigital capacitor length, the frequency of transmission poles of the filter can be tuned. The electromagnetic coupling mechanism in the components has been discussed. According to the results of the scattering parameters curve, the return loss at the transmission poles is more than 40 dB while the insertion loss in passbands is less than 0.3 dB.

The Compton camera has been developed to estimate high-energy gamma-ray sources distribution. The advantages of this modality over SPECT system are larger field of view, higher sensitivity, and wider energy range. All of the mentioned properties of this device caused to have special applications for use in nuclear medicine and especially hadron therapy. Image reconstruction in the Compton camera are more complex in comparison with conventional imaging systems. In this way, different methods based on the iteration method have been developed to reconstruct the images. In fact, image reconstruction in Compton camera is performed by using conical projections and cone surfaces which gamma rays are probably emitted from them. Finally, cone surfaces projected into the image matrix. The Compton scattering camera consists of two detectors, the detector closest to the source for the occurrence and recording of the Compton scattering in this detector, and the second detector located behind the primary detector (farther from the source) designed to absorbing  the scattered photons (by the first detector). Position, energy and interaction time are stored by both detectors. Opening angle and the apex of the Compton cone can be calculated by using the amount of energy deposition in the two detectors and the location of the interactions. By having cone characteristics, cone surface is projected into the image space which allows to estimate the values of the traversed voxels. In this way, 3-D distribution of the source could be acquired by single-shot and without collimator. In this paper, the results of the Compton camera simulation in the GATE code are presented along with the written reconstruction algorithm. Then the effects of the detector thickness variations are evaluated by using a simulated phantom consisting of four radioactive spheres with different diameters. Image reconstruction was performed using LM-MLEM algorithm, which is based on the iterative method, in MATLAB software. The results of the image analysis show that the characteristic of the detector in the Compton camera along with iteration number have a strong impact on image quality.