نشریه سنجش و ایمنی پرتو
سال دوازدهم شماره 1 (پیاپی 45، بهار 1402)

One of the best methods for detecting breast cancer, especially in its early stages, is X-ray mammography. However, few studies have examined the risk of developing cancer in tissues other than the breast. The aim of the current study is to determine the absorbed dose in sensitive body organs during mammography. Simulation was performed using the GATE code. In the first step, an X-ray tube was created to produce suitable energy spectra for mammography. Then, a quality control phantom was designed to assess image quality, including spatial resolution and contrast-to-noise ratio (CNR). An adult ORNL phantom with different organs was designed, and the geometry of a digital mammography device was simulated in two main mammography views (CC and MLO) to calculate the dose in the organs. Finally, it was found that the radiation dose to body tissues such as the uterus, which is outside the primary X-ray field, is low (on average 0.022 μGy). However, the highest dose is received by the contralateral breast, about 2735.5 μGy, in the lungs about 48.9 μGy, in the heart about 7.6 μGy and in the stomach about 5.8 μGy after the examined breast and tumor. Based on the results, in our study, the energy of 25 keV is introduced as the optimal energy.

In the present research, the increase of nuclear spin effects on the fission barrier was studied for different nuclei. Then, the deposited energy in the target was calculated using MCNPX code. Based on F7 tally, the released energies due to fission and the neutron production rate were measured for 238,240,242,244Pu, 242,244,246,248Cm and 252,254Cf isotopes. It was shown that by increasing the spin of nuclei from 4+ to 26+, the rate of neutron production for different isotopes also increases. The simulation results showed that the increase in the energy of incident neutrons is proportional to the increase in the spin of the target nucleus. At last, the mutual effect of increasing spin on the nuclear deformation was investigated which indicates a good agreement with the simulation results. One of the most important results of this work is that neutron collision with any energy increases the spin of nucleus. Finally, based on the comparison, it was found that the results of CNS (Cranked Nilsson-Strutinsky) code are confirmed with that of MCNPX.

Skeletal metastases are prevalent complications related to patients with solid tumor cancer. Till now several boneseeking radiopharmaceuticals have been developed for bone metastases. Interesting features of bisphosphonates attracted attentions to them in the field of radiopharmaceutical therapy and studies on new generation of them have been doing too. The aim of this study was to produce and quality control of a radiopharmaceutical made with ibandronate as the third generation of bisphosphonates. For this purpose, Ibandronate was labeled with beta-emitting radionuclide of rhenium-188. Radionuclide purity was investigated using gamma spectrometry and radiochemical purity by thin layer chromatography. Finally, the biodistribution of this radiopharmaceutical was evaluated in mice. The results showed that the radiochemical purity of this compound is about 97%. the highest uptake (ID/g) was related to bone and the amount of this uptake was 7.11% at 12 hours after injection. The kidneys and stomach were the two organs that had the most activity after bone. Considering the possibility of producing the 188Re-IBA radiopharmaceutical, as well as the proper distribution of this radiopharmaceutical in target and non-target organs, it can be concluded that the ibandronate as the third generation of bisphosphonates this radiopharmaceutical can be useful in the bone metastases treatment.

Lead and hot cell equipment are needed to perform radiochemical processes to extract the desired radioisotope from the hot target. The proper design and shielding of this equipment are important to reduce the radiation exposure of employees. In this article, based on the gamma rays emitted from the hot target used in the molybdenum-99 production process, the calculations related to the design of a suitable shield for a chamber with specific dimensions made of Barite Concrete to make a hot cell or made of Lead to make a lead cell, has been done. The simulation results with MCNP6.2 Monte Carlo code show that the shield thickness to limit the dose rate to 10 µSv/h, for making hot cell or lead cells equals 90 cm and 24 cm, respectively.

Microdosimetry is an approach that can be very effective in improving the quality of radiation therapy. Based on the possible concept of deposited energy in microbiological tissues and environments, this knowledge can help to calculate and examine the quantities related to the effect of radiation. In this research, using the Geant4-DNA code in conjunction with experimental cross-sections and the µ-randomness method, the microdosimetry quantities known as the frequency-mean lineal energy and frequency-mean specific energy were calculated for low-energy electrons. The calculations concerned cylinders that are comparable in size with living organisms such as DNA, nucleosome, and chromatin fiber, distributed randomly in a sphere of water with a diameter of about the average size of the nucleus of human cells. The results were compared with the ones obtained based on the default cross-sections of Geant4-DNA. We found that the average values of (frequency-mean) lineal and specific energy calculated with experimental cross-sections were larger than those calculated with default cross sections. The maximum difference of these quantities was observed, in the so-called small and medium cylinders, at 0.1 keV and, in the large cylinder, at 0.3 keV. Also, for a volume comparable in size to DNA, a good correspondence between the results of frequency-mean lineal energy with experimental cross-sections and the electron DNA-damage in the cell was observed.

The use of brachytherapy using ophthalmic plaques due to their lower cost, and ease of access compared to other radiotherapy methods is widely used to treat various types of eye malignancies, especially uvea melanoma (iris, ciliary body, and choroid). Beta emitter applicators of 106Ru/106Rh, have a lot of use in brachytherapy of intraocular tumors. Treating eye melanomas using beta-emitting 106Ru/106Rh plaques in Europe and Iran is popular. Estimating the dose distribution of eye plaques according to the location of the tumor is of great importance. In this study, two 106Ru/106Rh betta emitter concave eye plaque models, CCA and CCB, manufactured by the BEBIG Eckert & Ziegler BEBIG GmbH Company, were simulated using GATE Monte Carlo simulation code. Knowledge of the exact dose distributions in tumors and each organ at risk is critical in eye plaque brachytherapy for uveal melanoma treatment. In this regard, an eye phantom includes different parts sclera, choroid, retina, cornea, vitreous, optic nerve, lens, cornea, anterior chamber, and a tumor with thickness of 3 mm and a base diameter of 10 mm, were modeled using the GATE Monte Carlo simulation code. For validation purposes, at first, the energy spectrum of the 106Ru/106Rh source used in the study was verified as an isotropic point source centered in a water phantom using beta particles with a maximum energy of 3.54 MeV. Then the plaque central axis depth dose in the eye phantom was calculated using GATE and compared with available data. Furthermore, the difference between the deposited dose in the different components of the eye phantom shows that due to its smaller dimensions, the CCA eye plaque not only causes more concentration of the dose deposition in the tumor tissue but also greatly reduces the dose reaching structures such as the lens, as a sensitive volume.