نشریه سنجش و ایمنی پرتو
سال یازدهم شماره 2 (پیاپی 42، تابستان 1401)

This radiological monitoring system consisting of a 2-inch NaI(Tl) crystal coupled to a PM tube and mounted on a multi-rotor UAV has been developed to fast detect radioactive sources. To assess its performance, a set of experiments for the detection of low-level Co-60 and Cs-137 point sources in a soccer field was performed. Then, the radiological map was made and then fused with the geographical one using image processing techniques. The results show that at 50 cm, all 5-point sources were successfully identified in their actual locations. By decreasing the flight height, the ability of the drone-based radiological monitor in recognizing radioactive sources significantly increases. The results confirmed that the drone system with the scintillation detector enabled the accurately identifying radiological anomalies by surveying a contaminated area.

Nuclear accidents are sometimes unavoidable, but the risks can be significantly reduced with preparedness and prudence. Therefore one must have a proper assessment of the consequences of the accident. In this research, a three-dimensional simulation of the reactor core has been used to estimate the leakage rate of radioisotopes in case of the worst accident in the Bushehr nuclear power plant. The main parameters of the Bushehr reactor core simulation were benchmarked with the FSAR. Then the time-dependent activity and the isotopes are assumed as the source term for the accident, and the incident of complete melting of the reactor core and the entry of all pollutants into the environment was calculated. Activity changes over time were calculated for 18 years after the accident.Furthermore, by examining more than a hundred radioisotopes, the most active ones were figured out. Results were calculated for these isotopes' source terms over time up to 18 years after the accident. Finally, specific activity caused by each of the important isotopes was presented in order to prioritize the elimination of contaminants. Calculations were done using the MCNPX2.7.E code and considering the Burn card.

Specific absorbed fraction is one of the important parameters for estimating the internal dose. In this paper, the specific absorbed fraction for a number of body organs has been calculated using the Zubal Voxel phantom. The GATE Monte Carlo code version 7.2 was used to simulate the single-energy photons and electrons related to the radioactive isotope 177Lu. kidney, liver, and spleen were considered as source organs in this simulation and the specific absorbed fractions of these source organs were compared with the values ​​obtained from previous studies. The most relative difference between the values of this study and previous studies was observed to be 41% and related to the photons with the energy of 71 keV when the spleen and liver were considered as the source and target organs, respectively. In most data, discrepancies are acceptable and the obtained data are consistent with the previous data and have been verified. Using the data obtained from this study, the S-factors used for dosimetric calculations in the MIRD method were calculated and presented.

Intraoperative electron radiotherapy (IOERT) is a relatively new method of direct ionizing radiation to the tumor or tumor bed during surgery. In order to properly treat the intended target, it is necessary to examine the radiation dose curves and the shield used to protect healthy tissues and organs. In particular, radiation therapy during breast surgery requires the protection of critical tissues within the field and underlying the target volume such as the heart and lungs. In this case, a thin layer of high-Z material is placed between the treated (breast) tissue and the underlying vital tissue. The breast, lung, and radiation shield were geometrically considered as three coaxial cylinders. Using the MCNPX code, breast tissue, shield, and lung were irradiated with 6, 9, and 12 MeV electrons. The flux and dose of electrons and secondary photons in different tissues were calculated. Investigations showed that for 6 MeV electrons, the use of shielding has a negligible effect on the amount of dose received by the tissues around the breast. At energies of 9 and 12 MeV, Al-Pb shielding and St-PMMA shielding have almost the same performance in reducing the amount of dose received by the tissues around the breast. At the energy of 18 MeV, the Al-Pb shielding has a better performance than the St-PMMA shielding in reducing the dose received by the organs adjacent to the breast tissue.

Adjacent radiation fields are applied in some radiotherapeutic cases. When using these radiation fields, considerable dose errors across the junction of radiation fields are possible. Therefore, it is necessary to evaluate the accuracy of the dose calculated by the treatment planning system (TPS) when using the adjacent radiation fields. The present study aimed to quantify the dose calculation accuracy of ISOgray TPS for the photon-photon adjacent fields. To assess the accuracy of dose calculations, the dose profiles were first measured by a Semiflex TM31010 at 1, 1.5, 5, and 10 cm depths for different field sizes (6 × 6, 10 × 10, and 20 × 20 cm2). In the second step, corresponding data were extracted from the ISOgray TPS. Finally, the dosimetric performance of TPS was evaluated using a gamma index analysis. The overall dose calculation accuracy of ISOgray TPS was within the acceptable range for the build-up region (with acceptance criteria of dose difference (DD) = 15% and distance to agreement (DTA) =3 mm) and the depths after the build-up region (with acceptance criteria of DD = 5% and DTA = 3 mm). Moreover, the overall accuracy of dose calculations was not affected by the field size. A more detailed analysis of the findings revealed that the accuracy of dose calculations in the match line regions of the adjacent radiation fields for 1cm beam profiles was within the acceptable range; however, it declined for other depths. The findings showed that the overall dose calculation accuracy of ISOgray TPS was acceptable for evaluated adjacent radiation fields. However, the accuracy of dose calculations in the match line regions of the adjacent radiation fields for the depth after build-up was not within the acceptable range.

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.