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  • Author: Mahdi Ghorbani x
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Abstract

Due to the application of coil-shaped coils in a compressed gas flow exchanger and water pipe flow in airconditioner devices, air conditioning and refrigeration systems, both industrial and domestic, need to be optimized to improve exchange capacity of heat exchangers by reducing the pressure drop. Today, due to the reduction of fossil fuel resources and the importance of optimal use of resources, optimization of thermal, mechanical and electrical devices has gained particular importance. Compressed heat exchangers are the devices used in industries, especially oil and petrochemical ones, as well as in power plants. So, in this paper we try to optimize compressed heat exchangers. Variables of the functions or state-of-the-machine parameters are optimized in compressed heat exchangers to achieve maximum thermal efficiency. To do this, it is necessary to provide equations and functions of the compressed heat exchanger relative to the functional variables and then to formulate the parameter for the gas pressure drop of the gas flow through the blades and the heat exchange surface in relation to the heat duty. The heat transfer rate to the gas-side pressure drop is maximized by solving the binary equation system in the genetic algorithm. The results show that using optimization, the heat capacity and the efficiency of the heat exchanger improved by 15% and the pressure drop along the path significantly decreases.

Dosimetric characterizations of GZP6 60Co high dose rate brachytherapy sources: application of superimposition method

Background. Dosimetric characteristics of a high dose rate (HDR) GZP6 Co-60 brachytherapy source have been evaluated following American Association of Physicists in MedicineTask Group 43U1 (AAPM TG-43U1) recommendations for their clinical applications.

Materials and methods. MCNP-4C and MCNPX Monte Carlo codes were utilized to calculate dose rate constant, two dimensional (2D) dose distribution, radial dose function and 2D anisotropy function of the source. These parameters of this source are compared with the available data for Ralstron 60Co and microSelectron192Ir sources. Besides, a superimposition method was developed to extend the obtained results for the GZP6 source No. 3 to other GZP6 sources.

Results. The simulated value for dose rate constant for GZP6 source was 1.104±0.03 cGyh-1U-1. The graphical and tabulated radial dose function and 2D anisotropy function of this source are presented here. The results of these investigations show that the dosimetric parameters of GZP6 source are comparable to those for the Ralstron source. While dose rate constant for the two 60Co sources are similar to that for the microSelectron192Ir source, there are differences between radial dose function and anisotropy functions. Radial dose function of the 192Ir source is less steep than both 60Co source models. In addition, the 60Co sources are showing more isotropic dose distribution than the 192Ir source.

Conclusions. The superimposition method is applicable to produce dose distributions for other source arrangements from the dose distribution of a single source. The calculated dosimetric quantities of this new source can be introduced as input data to the GZP6 treatment planning system (TPS) and to validate the performance of the TPS.

Abstract

The aim of this study is the evaluation of electron dose enhancement and photon contamination production by various nanoparticles in the electron mode of a medical linac. MCNPX Monte Carlo code was used for simulation of Siemens Primus linac as well as a phantom and a tumor loaded with nanoparticles. Electron dose enhancement by Au, Ag, I and Fe2O3 nanoparticles of 7, 18 and 30 mg/ml concentrations for 8, 12 and 14 MeV electrons was calculated. The increase in photon contamination due to the presence of the nanoparticles was evaluated as well. The above effects were evaluated for 500 keV and 10 keV energy cut-offs defined for electrons and photons. For 500 keV energy cut-off, there was no significant electron dose enhancement. However, for 10 keV energy cut-off, a maximum electron dose enhancement factor of 1.08 was observed for 30 mg/ml of gold nanoparticles with 8 MeV electrons. An increase in photon contamination due to nanoparticles was also observed which existed mainly inside the tumor. A maximum photon dose increase factor of 1.07 was observed inside the tumor with Au nanoparticles. Nanoparticles can be used for the enhancement of electron dose in the electron mode of a linac. Lower energy electron beams, and nanoparticles with higher atomic number, can be of greater benefit in this field. Photons originating from nanoparticles will increase the photon dose inside the tumor, and will be an additional advantage of the use of nanoparticles in radiotherapy with electron beams.

Abstract

Aim

The aim of this study is to quantify the influence of the photon energy spectrum of brachytherapy sources on task group No. 43 (TG-43) dosimetric parameters.

Background

Different photon spectra are used for a specific radionuclide in Monte Carlo simulations of brachytherapy sources.

Materials and methods

MCNPX code was used to simulate 125I, 103Pd, 169Yb, and 192Ir brachytherapy sources. Air kerma strength per activity, dose rate constant, radial dose function, and two dimensional (2D) anisotropy functions were calculated and isodose curves were plotted for three different photon energy spectra. The references for photon energy spectra were: published papers, Lawrence Berkeley National Laboratory (LBNL), and National Nuclear Data Center (NNDC). The data calculated by these photon energy spectra were compared.

Results

Dose rate constant values showed a maximum difference of 24.07% for 103Pd source with different photon energy spectra. Radial dose function values based on different spectra were relatively the same. 2D anisotropy function values showed minor differences in most of distances and angles. There was not any detectable difference between the isodose contours.

Conclusions

Dosimetric parameters obtained with different photon spectra were relatively the same, however it is suggested that more accurate and updated photon energy spectra be used in Monte Carlo simulations. This would allow for calculation of reliable dosimetric data for source modeling and calculation in brachytherapy treatment planning systems.

Background. The aim of this study is to evaluate the performance of a color scanner as a radiochromic film reader in two dimensional dosimetry around a high dose rate brachytherapy source.

Materials and methods. A Microtek ScanMaker 1000XL film scanner was utilized for the measurement of dose distribution around a high dose rate GZP6 60Co brachytherapy source with GafChromic® EBT radiochromic films. In these investigations, the non-uniformity of the film and scanner response, combined, as well as the films sensitivity to scanner’s light source was evaluated using multiple samples of films, prior to the source dosimetry. The results of these measurements were compared with the Monte Carlo simulated data using MCNPX code. In addition, isodose curves acquired by radiochromic films and Monte Carlo simulation were compared with those provided by the GZP6 treatment planning system.

Results. Scanning of samples of uniformly irradiated films demonstrated approximately 2.85% and 4.97% nonuniformity of the response, respectively in the longitudinal and transverse directions of the film. Our findings have also indicated that the film response is not affected by the exposure to the scanner’s light source, particularly in multiple scanning of film. The results of radiochromic film measurements are in good agreement with the Monte Carlo calculations (4%) and the corresponding dose values presented by the GZP6 treatment planning system (5%).

Conclusions. The results of these investigations indicate that the Microtek ScanMaker 1000XL color scanner in conjunction with GafChromic EBT film is a reliable system for dosimetric evaluation of a high dose rate brachytherapy source.

Abstract

Background: Ionizing radiation has an indispensable role in diagnostic radiology and clinical treatments. Apparently, medical exposure in diagnostic radiology pertains to be the preeminent man-made source of radiation.

Objective: The aim of the present scientific study is to calculate the Entrance Surface Dose (ESD) and Effective Dose (ED) in digital radiography in Mazandaran province.

Materials and methods: The study was performed on 3600 patients in digital X-ray rooms 15 hospitals and the required data were collected from two age groups (10>15 years and adults) in each projection. Based on the results of this study, ESD and ED were calculated for skull (PA), skull (lateral), cervical spine (AP), cervical spine (lateral), chest (PA), chest (lateral), abdomen (AP), lumbar spine (AP), lumbar spine (lateral), pelvis (AP), thoracic spine (AP) and thoracic spine (lateral) examinations. It was calculated using PCXMC software (version 2.0).

Results: In this study, mean ESDs for the 10-15 year group varied from 0.97±0.21 mGy to 3.62±1.38 mGy for chest (PA) and lumbar spine (lateral), respectively. For the adult group varied from 1.05±0.31 to 3.85±1.44 for cervical spine (AP) and lumbar spine (lateral), respectively. And also ED value was from in the range of 10.40 µSv to 378.46 µSv for skull (PA) 10-15 year group and abdomen adults, respectively

Conclusion: This survey revealed a significant variation in the radiation dose of digital radiology examinations among hospitals in Mazandaran province. Application of a dose reference level (DRL) could be an optimization procedure for reducing the patient’s dose in Mazandaran province.

Abstract

Background

Interstitial rotating shield brachytherapy (I-RSBT) is a recently developed method for treatment of prostate cancer. In the present study TG-43 dosimetric parameters of a 153Gd source were obtained for use in I-RSBT.

Materials and methods

A 153Gd source located inside a needle including a Pt shield and an aluminum window was simulated using MCNPX Monte Carlo code. Dosimetric parameters of this source model, including air kerma strength, dose rate constant, radial dose function and 2D anisotropy function, with and without the shields were calculated according to the TG-43 report.

Results

The air kerma strength was found to be 6.71 U for the non-shielded source with 1 GBq activity. This value was found to be 0.04 U and 6.19 U for the Pt shield and Al window cases, respectively. Dose rate constant for the non-shielded source was found to be 1.20 cGy/(hU). However, for a shielded source with Pt and aluminum window, dose rate constants were found to be 0.07 cGy/(hU) and 0.96 cGy/(hU), on the shielded and window sides, respectively. The values of radial dose function and anisotropy function were tabulated for these sources. Additionally, isodose curves were drawn for sources with and without shield, in order to evaluate the effect of shield on dose distribution.

Conclusions

Existence of the Pt shield may greatly reduce the dose to organs at risk and normal tissues which are located toward the shielded side. The calculated air kerma strength, dose rate constant, radial dose function and 2D anisotropy function data for the 153Gd source for the non-shielded and the shielded sources can be used in the treatment planning system (TPS).

Abstract

Background. In December, 2019, China, has experienced an outbreak of novel coronavirus disease 2019 (COVID-19). Coronavirus has now spread to all of the continents. We aimed to consider clinical characteristics, laboratory data of COVID-19 that provided more information for the research of this novel virus.

Methods. We performed a retrospective cohort study on the clinical symptoms and laboratory findings of a series of the 100 confirmed patients with COVID-19. These patients were admitted to the hospitals affiliated to Babol University of Medical Sciences (Ayatollah Rohani, Shahid Beheshti and Yahyanejad hospitals) form 25 February 2020 to 12 March 2020.

Results. Nineteen patients died during hospitalization and 81 were discharged. Non-survivor patients had a significantly higher C-reactive protein (CRP) (MD: 46.37, 95% CI: 20.84, 71.90; P= 0.001), white blood cells (WBCs) (MD: 3.10, 95% CI: 1.53, 4.67; P< 0.001) and lower lymphocyte (MD: -8.75, 95% CI: -12.62, -4.87; P< 0.001) compared to survivor patients Data analysis showed that comorbid conditions (aRR: 2.99, 95%CI: 1.09, 8.21, P= 0.034), higher CRP levels (aRR: 1.02, 95%CI: 1.01, 1.03, P= 0.044), and lower lymphocyte (aRR: 0.82, 95%CI: 0.73, 0.93, P= 0.003) were associated with increased risk of death.

Conclusions. Based on our findings, most non-survivors are elderly with comorbidities. Lymphopenia and increased levels of WBCs along with elevated CRP were associated with increased risk of death. Therefore, it is best to be regularly assessed these markers during treatment of COVID-19 patients.