Application of Monte Carlo simulation in radiation dose estimation and optimization for diagnostic radiology / 中华放射医学与防护杂志

The increasing frequency of radiographic diagnostic imaging and the cumulative dose to the public from radiation has raised widespread concerns. However, accurate measurement of the radiation dose received by the human body is difficult to achieve. Monte Carlo simulation, as a numerical computational method guided by probability statistics theory, has been applied to various dose assessments, imaging optimizations, and radiation protection in radiographic diagnostic imaging. We provide a comprehensive review of the principles of the Monte Carlo method, the modelling process of Monte Carlo simulation and the progress of its application to diagnostic radiological dose estimation.

Mechanical ventilator acquisition strategy in a large private tertiary medical center using Monte Carlo Simulation

Background and Objectives@#Mechanical ventilators are essential albeit expensive equipment to support critically ill patients who have gone into respiratory failure. Adequate numbers should always be available to ensure that a hospital provides the optimal care to patients but the number of patients requiring them at any one time is unpredictable. Finding therefore the best balance in providing adequate ventilator numbers while ensuring the financial sustainability of a hospital is important.@*Methods@#A quantitative method using Monte Carlo Simulation was used to identify the optimal strategy for acquiring ventilators in a large private tertiary medical center in Metro Manila. The number of ventilators needed to provide ventilator needs 90% of the days per month (27/30) was determined using historical data on ventilator use over a period of four years. Four acquisition strategies were investigated: three ownership strategies (outright purchase, installment, and staggered purchase) and a rental strategy. Return on Investment (ROI), Internal Rate of Return (IRR), Modified Internal Rate of Return (MIRR), Net Present Value (NPV), and Payback period (or Breakeven Point) for each strategy were determined to help recommend the best strategy. A qualitative survey was also conducted among doctors, nurses, and respiratory therapists who were taking care of patients hooked to ventilators to find out their experiences comparing hospital-owned and rental ventilators.@*Results@#It was found that a total of 11 respirators were needed by the hospital to ensure that enough respirators were available for its patients at least 90% of the days in any month based on the previous four-year period. This meant acquiring three more ventilators as the hospital already owned eight. Among the strategies studied, projected over a 10-year period, the installment strategy (50% down payment with 0% interest over a 5-year period) proved to be the most financially advantageous with ROI = 9.36 times, IRR = 97% per year, MIRR = 26% per year, NPV = ₱39,324,297.60 and Payback period = 1.03 years). A more realistic installment strategy with 15% (paid quarterly or annually) and 25% annual interest rates were also explored with their financial parameters quite like but not as good as the 0% interest. The outright purchase of three ventilators came in lower (ROI = 4.53 times, IRR = 55% per year, MIRR = 19% per year, NPV = ₱38,064,297.60 and Payback period = 1.81 years) followed last by staggered purchase with ROI = 3.56 times, IRR = 64% per year, MIRR = 28% per year, NPV = ₱29,905,438.08, and payback period of 2.06 years. As there was no investment needed for the rental strategy, the only financial parameter available for it is the NPV which came out as ₱21,234,057.60. The qualitative part of the study showed that most of the healthcare workers involved in the care of patients attached to the ventilator were aware of the rental ventilators. The rental ventilators were generally described as of lower functionality and can more easily break down. The respondents almost uniformly expressed a preference for the hospital-owned ventilators.@*Conclusion@#This analysis showed that the best ventilator ownership strategy from a purely financial perspective for this hospital is by installment with a 50% down payment and 0% interest. Moderate rates of 15% and 25% interest per year were also good. These were followed by outright purchase and lastly by staggered purchase. The rental strategy gave the lowest cumulative 10-year income compared to any of the ownership strategies, but may still be considered good income because the hospital did not make any investment. However, it seems that most of the healthcare workers involved in taking care of patients on ventilators thought the rental ventilators were of lower quality and preferred the hospital-owned ventilators.

Relative bioavailability of cadmium in aquatic products and its application on the cadmium exposure risk assessment / 上海预防医学

ObjectiveTo understand the relative bioavailability （RBA） of cadmium in different aquatic products. Based on the consideration of the gender differences and the relative bioavailability of cadmium in different foods， the physiologically based toxicokinetic （PBTK） model of cadmium was further optimized and verified. The correlation between internal and external exposure in quantitative risk assessment of food safety was optimized， and the provisional tolerable daily intake （PTDI） value of cadmium was derived. MethodsThe relative bioavailability of cadmium in different aquatic products was determined in four-week-old Balb/c female mice. The PBTK model of cadmium metabolism was optimized by ABC-MCMC method using combined internal and external exposure data of cadmium in Shanghai residents， and the PTDI was calculated accordingly. ResultsExcept for scallops and squid， the RBA of aquatic samples was less than 1， indicating that the absorption rate of cadmium in aquatic products was lower than that of cadmium chloride. The higher RBA of squid and scallop may be due to the presence of cadmium in the visceral organs， which is conducive to cadmium absorption and its higher concentration of cadmium. Frying at the temperature less than 160 ℃ reduced cadmium absorption but may increase cadmium absorption at the temperature greater than 160 ℃. The optimized model parameters converged well and the model could reasonably estimate urinary cadmium level according to the external exposure of cadmium. The PTDI value was0.466 4 μg·（kg·day）-1 according to the optimized single-chamber model. ConclusionThe relative bioavailability of cadmium in different foods varies greatly， except for squid and scallops， RBA is less than 1， and cooking processing will affect the RBA of food. The construction of the PBTK model did not only consider the effects of gender differences on cadmium metabolism， but also included the relative bioavailability data to optimize and adjust the correlation coefficient of absorption rate. Compared with the model without RBA adjustment， the adjusted model has enhanced the ability to predict urinary cadmium level， which provides a new， more accurate method for the risk assessment of food safety.

Risk of false conformity decisions due to measurement uncertainty of Active Pharmaceutical Ingredient: A multiparametric evaluation

Abstract Medicines must be subject to physical, chemical, and biological analysis to guarantee their quality, safety, and effectiveness. Despite the efforts to ensure the reliability of analytical results, some uncertainty will always be associated with the measured value, which can lead to false decisions regarding conformity/non-conformity assessment. This work aims to calculate the specific risk of false decisions regarding conformity/non-conformity of acetaminophen oral solution dosage form. The acetaminophen samples from five different manufacturers (A, B, C, D, and E) were subject to an active pharmaceutical ingredient assay, density test, and dose per drop test according to the official compendia. Based on measured values and their respective uncertainties, the risk values were calculated using the Monte Carlo method implemented in an MS Excel spreadsheet. The results for two acetaminophen oral solution samples (C and D) provided an increased total risk value of false acceptance (33.1% and 9.6% for C and D, respectively). On the other hand, the results for the other three acetaminophen samples (A, B, and E) provided a negligible risk of false acceptance (0.004%, 0.025%, and 0.045% for A, B, and E, respectively). This indicates that measurement uncertainty is very relevant when a conformity assessment is carried out, and information on the risks of false decisions is essential to ensure proper decisions.

Nonparametric item response models: a comparison on recovering true scores / Modelos de resposta ao item não-paramétricos: comparando a recuperação de escores verdadeiros / Modelos de respuesta al item no-paramétricos: comparando la recuperación de puntuaciones verdaderas

Nonparametric procedures are used to add flexibility to models. Three nonparametric item response models have been proposed, but not directly compared: the Kernel smoothing (KS-IRT); the Davidian-Curve (DC-IRT); and the Bayesian semiparametric Rasch model (SP-Rasch). The main aim of the present study is to compare the performance of these procedures in recovering simulated true scores, using sum scores as benchmarks. The secondary aim is to compare their performances in terms of practical equivalence with real data. Overall, the results show that, apart from the DC-IRT, which is the model that performs the worse, all the other models give results quite similar to those when sum scores are used. These results are followed by a discussion with practical implications and recommendations for future studies.(AU)

Procedimentos não paramétricos são usados para adicionar flexibilidade aos modelos. Três modelos não paramétricos de resposta ao item foram propostos, mas não comparados diretamente: o Kernel smoothing (KS-IRT); a Curva Davidiana (DC-IRT); e o modelo semiparamétrico Rasch Bayesiano (SP-Rasch). O objetivo principal do presente estudo é comparar o desempenho desses procedimentos na recuperação de escores verdadeiros simulados, utilizando escores de soma como benchmarks. O objetivo secundário é comparar seus desempenhos em termos de equivalência prática com dados reais. De forma geral, os resultados mostram que, além do DC-IRT, que é o modelo que apresenta o pior desempenho, todos os outros modelos apresentam resultados bastante semelhantes aos de quando se usam somatórios. Esses resultados são seguidos de uma discussão com implicações práticas e recomendações para estudos futuros.(AU)

Se utilizan procedimientos no paramétricos para agregar flexibilidad a los modelos. Se propusieron tres modelos de respuesta al ítem no paramétricos, pero no se compararon directamente: Kernel smoothing (KS-IRT); la curva davidiana (DC-IRT); y el modelo bayesiano de Rasch semiparamétrico (SP-Rasch). El objetivo principal del presente estudio es comparar el desempeño de estos procedimientos en la recuperación de puntajes verdaderos simulados, utilizando puntajes de suma como puntos de referencia. El objetivo secundario es comparar su desempeño en términos de equivalencia práctica con datos reales. En general, los resultados muestran que, a excepción de DC-IRT, que es el modelo con peor desempeño, todos los otros modelos presentan resultados bastante similares a los obtenidos cuando se utilizan sumatorios. Estos resultados son seguidos por una discusión con implicaciones prácticas y recomendaciones para estudios futuros.(AU)

Propuesta metodológica para el uso del programa PCXMC 2.0 en modalidad rotacional / Methodological Proposal for the use of the program PCXMC 2.0 in Rotational Mode

RESUMEN Durante los procedimientos intervencionistas que utilizan fluoroscopia, se entrega a los pacientes diferentes niveles de dosis de radiación, que pueden tener un impacto a corto, mediano o largo plazo, así como en su severidad. Esto en función del tipo de radiación utilizada y de la sensibilidad a la radiación del tipo(s) de órgano(s) irradiado, es en este punto que se vuelve determinante conocer la dosis a órganos entregada durante los procedimientos con el fin de asegurar el bienestar de los pacientes, este procedimiento no se puede realizar directamente en los órganos del paciente, por lo que se utilizan programas especializado en cálculos dosimétricos. El software PCXMC 2.0 logra estimar la dosis efectiva a través del método determinístico Monte Carlo, a su vez, agregando la dosis equivalente y evaluación de riesgo para estudios dosimétricos, por lo cual, el objetivo del presente trabajo fue proponer una metodología estandarizada para la utilización del programa PCXMC en el cálculo de estas dos magnitudes

ABSTRACT During interventional procedures that utilize fluoroscopy, patients are exposed to varying levels of radiation doses, which can have short, medium, or long term impacts, as well as varying severities. This depends on the type of radiation used and the radiation sensitivity of the organ(s) being irradiated. At this point, it becomes crucial to determine the organ doses delivered during procedures in order to ensure patient well-being. Since direct measurements cannot be made on the patient's organs, specialized software is used for dosimetric calculations. PCXMC 2.0 software achieves the estimation of effective dose through the deterministic Monte Carlo method, while also incorporating equivalent dose and risk assessment for dosimetric studies. Therefore, the objective of this work was to propose a standardized methodology for the use of the PCXMC 2.0 sofware in the calculation of these two magnitudes.it is important to outline a working method for this software and provide instructions on its operation

Contamination status and exposure risk of mycotoxins in Coicis Semen / 中国中药杂志

By investigating the contamination status and predicting the exposure risk of mycotoxin in Coicis Semen, we aim to provide guidance for the safety supervision of Chinese medicinal materials and the formulation(revision) of mycotoxin limit standards. The content of 14 mycotoxins in the 100 Coicis Semen samples collected from five major markets of Chinese medicinal materials in China was determined by UPLC-MS/MS. The probability evaluation model based on Monte Carlo simulation method was established after Chi-square test and One-way ANOVA of the sample contamination data. Health risk assessment was performed on the basis of margin of exposure(MOE) and margin of safety(MOS). The results showed that zearalenone(ZEN), aflatoxin B_1(AFB_1), deoxynivalenol(DON), sterigmatocystin(ST), and aflatoxin B_2(AFB_2) in the Coicis Semen samples had the detection rates of 84%, 75%, 36%, 19%, and 18%, and the mean contamination levels of 117.42, 4.78, 61.16, 6.61, and 2.13 μg·kg~(-1), respectively. According to the limit standards in the Chinese Pharmacopoeia(2020 edition), AFB_1, AFs and ZEN exceeded the standards to certain extents, with the over-standard rates of 12.0%, 9.0%, and 6.0%, respectively. The exposure risks of Coicis Semen to AFB_1, AFB2, ST, DON, and ZEN were low, while 86% of the samples were contaminated with two or more toxins, which needs more attention. It is suggested that the research on the combined toxicity of different mycotoxins should be strengthened to accelerate the cumulative exposure assessment of mixed contaminations and the formulation(revision) of toxin limit standards.

In vitro pharmacodynamic study of ceftobiprole, vancomycin, linezolid and daptomycin against staphylococcal bloodstream infections / 中华传染病杂志

Objective:To evaluate the antibacterial efficacy of ceftobiprole, vancomycin, linezolid, and daptomycin against Staphylococcus aureus (SAU) and coagulase-negative Staphylococcus (CNS) bloodstream infections, which can provide a reference for clinical medication. Methods:A total of 1 777 strains of staphylococci were isolated from blood culture of 51 hospitals within the Blood Bacterial Resistant Investigation Collaborative System (BRICS) from January to December in 2021. The dilution method was used to assess the minimum inhibitory concentrations (MIC) of ceftobiprole, vancomycin, linezolid and daptomycin on staphylococci. Additionally, the probability of target attainment (PTA) and cumulative fraction of response (CFR) of these medications in varied dosage regimens were predicted using Monte Carlo simulation.Results:Ceftobiprole demonstrated significant antibacterial activity against methicillin-resistant Staphylococcus aureus(MRSA), the MIC 50 and MIC 90 were 0.500 and 1.000 mg/L, respectively, and the MIC range was ≤0.060 to 4.000 mg/L.Meanwhile, the ceftobiprole-resistance rate of SAU was 0.1%(1/1 073), but the resistance rate of CNS was 7.7%(54/704). There was no evidence of staphylococcal resistance to daptomycin or vancomycin. Against methicillin-sensitive Staphylococcus aureus (MSSA), no resistance to the four drugs was observed. Monte Carlo simulation showed that standard drug regimens of ceftobiprole (500 mg once every eight hours) and daptomycin (6 mg·kg -1·d -1) achieved high PTA and CFR against staphylococcus.The current vancomycin and linezolid standard treatment for staphylococcal bloodstream infections had a low CFR. When vancomycin 1 000 mg once every eight hours was used, the CFRs of MRSA and MSSA were both≥90.0%, while the CFR of CNS was still less than 80.0%. CFR of linezolid against staphylococcus was ≥90.0% under the dosages of 600 mg once every eight hours. Conclusions:Ceftobiprole, vancomycin, linezolid and daptomycin all show strong antibacterial activity against staphylococcus.Ceftobiprole and daptomycin standard treatment represent adequate antibacterial efficacy against staphylococcal bloodstream infections. Furthermore, appropriate increase of the dosages of vancomycin and linezolid based on the MIC value and species of bacteria is necessary.

Monte Carlo simulation of photoneutron for a 15 MV medical linear accelerator / 中华放射医学与防护杂志

Objective:To study the photoneutron radiation field caused by photonuclear reaction during the operation of high energy medical linac.Methods:Monte Carlo was used to simulate the photoneutron pollution of Clinic 2300CD medical electron accelerator in 15 MV X-ray mode. The photoneutron spectrum at different positions of the head and the variation in neutron ambient dose equivalent in different irradiation fields were investigated, and the dose distribution of photoneutron on the isocenter plane and the dose attenuation in the water model were analyzed.Results:When the collimator was closed, the average photoneutron energy at the lower surface of target, primary collimator, flattening filter and multi-leaf collimator was 1.08, 1.20, 0.35 and 0.30 MeV, respectively. The neutron ambient dose equivalent at the isocenter first increased and then decreased with the irradiation field expanding, reaching the maximum in about 30 cm × 30 cm irradiation field. With the increase in the depth of the measuring point in water phantom, the neutron fluent first increased and then decreased, while the neutron dose gradually decreased. In different irradiation fields, the photoneutron dose rate was almost close to the background when the depth of the water was 20 cm.Conclusions:By exploring the photoneutron spectrum and dose distribution characteristics of the high energy medical linac head, as well as the dose deposition mechanism of photoneutron in water phantom, this study provides data support for further research on the additional dose and secondary cancer effects on patients caused by photoneutron pollution from the high energy medical linac.

Development of environmentally friendly flexible medical X-ray shielding materials and analysis and optimization of their protective performance / 中华放射医学与防护杂志

Objective:To develope and analyze and optimize the performance of some kinds of environmentally friendly flexible X-ray protective materials in attempt to tackle the various environmental and high energy consumption problems in the development of traditional medical X-ray protective clothing.Methods:The Monte Carlo program was used to establish a simplified model of medical X-ray tube. The aim was to carry out numerical simulation and prediction of the shielding materials′ performance against X-ray, prepare the flexible X-ray shielding materials through experiments and test and verify the their shielding performances The development and optimization path was also obtained by comparing the result between simulation and experiment.Results:Bi was the preferred alternative to toxic Pb elements, while W was able to compensate for weak X-ray absorption zone of Bi. The shielding efficiency of the composite material doped with 25% Bi+ 25% W was able to reach 77.8% and 66.3% at 80 and 120 kV p tube voltages, respectively. Conclusions:With both the selection of elements and the optimization of functional particles, the combination of W and Bi is an economical, environmentally friendly, and efficient shielding way within the energy range of medical diagnostic X-rays. The numerical simulation helps reduce experimental costs, shorten the research period, and improve the design efficiency of X-ray shielding materials.

Analysis of factors influencing the medical insurance balance of hospitalization expenses for gastric cancer surgery patients under DRG payment / 中华医院管理杂志

Objective:To analyze the influencing factors of the medical insurance balance of hospitalization expenses for gastric cancer surgery patients under DRG payment, for reference for promoting the reform of DRG payment in public hospitals and controlling hospitalization expenses reasonably.Methods:The gastric cancer patients enrolled in the gastroenterology department of a tertiary comprehensive hospital from January to July 2022 were selected as the research subjects. The indicators such as patient age, medical insurance balance, hospitalization expenses and their composition were extracted from the hospital information management system and the medical insurance settlement system a certain city. Descriptive analysis was conducted for all data, and stepwise multiple linear regression was used to analyze the influencing factors of patients′ medical insurance balance. Monte Carlo simulation method was used to simulate different combination scenarios of various influencing factors to analyze the probability of medical insurance balance.Results:A total of 205 patients were contained, including 117 in the medical insurance balance group and 88 in the loss group. The difference in hospitalization expenses and medical insurance balance between the two groups of patients were statistically significant ( P<0.05). The intervention of medical insurance specialists, correct DRG enrollment, parenteral nutrition preparation costs, anti infective drug costs, examination costs, and consumables costs were the influencing factors of patient medical insurance balance ( P<0.05). Through Monte Carlo simulation verification, patients with different cost parenteral nutrition preparations, or different anti infective drug schemes had the higher probability of medical insurance balance in the scenario where the medical insurance commissioner intervenes and the DRG enrollment was correct. Conclusions:The hospital adopted interventions from medical insurance specialists to ensure the correct DRG enrollment of patients, accurate use of parenteral nutrition and anti infective drugs, and reasonable control the cost of examinations and consumables, which could increase the probability of medical insurance balance for gastric cancer surgery patients. In the future, hospitals should further promote the procurement of drug consumables in bulk, reduce unnecessary examinations, develop standardized perioperative nutritional interventions and anti infection treatment pathways, ensure the accuracy of DRG enrollment, optimize clinical diagnosis and treatment pathways to improve the efficiency of medical insurance fund utilization and provide high-quality medical services for patients.

Evaluation of the dosing regimen of meropenem in elderly patients with renal insufficiency with Monte Carlo simulation / 中国药房

OBJECTIVE To explore the appropriate dosing regimen of meropenem in the elderly with renal insufficiency. METHODS The meropenem population pharmacokinetics of the two-compartment model of elderly patients were applied for Monte Carlo simulation. The model included the effect of renal function on the parameters. The designed dosages were 0.5， 1， 2 g； the administration modes included intravenous injection （lasting for 6 min） and intravenous drip （0.5， 3 h）； the administration frequencies were q12 h， q8 h. A total of 18 dosing regimens were designed. The probability of target attainment of %fT＞4MIC≥40% and Cmin≤27.5 mg/L were calculated respectively to optimize the dosing regimen. RESULTS For elderly patients with creatinine clearance （CLcr） ≤40 mL/min， when the minimum inhibitory concentration （MIC） was equaled to 1 mg/L， the suggested dosing regimens were “0.5 g， intravenous drip 0.5 h， q12 h”“ 1 g， intravenous injection， q12 h”. When the MIC was equaled to 2 mg/L， the suggested dosing regimens were “0.5 g， intravenous injection， q8 h”“ 1 g， intravenous drip 0.5 h， q12 h”. When the MIC was equaled to 4， 8 mg/L， the suggested dosing regimens were “1 g （or 2 g）， intravenous injection， q8 h”. For elderly patients with CLcr equal to 50 mL/min， when the MIC was equaled to 1 mg/L， the suggested dosing regimens were “0.5 g， intravenous injection， q8 h“”1 g， intravenous injection， q12 h”. When the MIC was equal to 2， 4， 8 mg/L，the suggested dosing regimens were“0.5 g （or 1 g， or 2 g）， intravenous drip for 0.5 h， q8 h”. The appropriate dosing regimens of all the above protocols were above 96.6%. In the dosing regimen of “2 g，intravenous injection or intravenous drip 0.5 h， q8 h”， Cmin＞27.5 mg/L occurred in 40 times among the 1 000 times of simulation， indicating adverse reactions of the nervous system may occur. CONCLUSIONS For the elderly patients with renal insufficiency， the dosing regimen of meropenem should be adjusted accordingly with CLcr＝40 mL/min as the boundary， and the toxicity of nervous system should be considered at the same time.

Evaluation of tegacycline regimens in treatment of gram-negative bacterial infections with Monte Carlo simulation / 中国临床药理学与治疗学

AIM: To evaluate the dose regimens of tegacycline for treatment of hospital-acquired pneumonia, complex abdominal infection and complex skin and soft tissue infection caused by Gram-negative bacterial infections with Monte Carlo model. METHODS: The minimum inhibitory concentrations (MICs) of tegacycline against Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae and Enterobacter cloacae were collected from the CHINET in 2018. The target probability (PTA) and cumulative response fraction (CFR) of different regimens were calculated using Monte Carlo simulation based on PK/PD theory of tegacycline. RESULTS:In the treatments of HAP caused by gram-negative bacteria, when MIC≤0.5 μg / mL, the PTA of 50 mg q12h was greater than 90%, and when MIC≥1 μg / mL, PTA and CFR of 100 mg q12h were both greater than 90%, When MIC≥2 μg/mL, 50 mg q12h, 75 mg q12h and 100 mg q12h doses of PTA were less than 90%. In the treatment of cIAI, when MIC≤0.5 μg / mL, PTA of 50 mg q12h reached the target value, and when MIC=1 μg/mL, PTA of 100 mg q12h was greater than 90%. For complex skin and soft tissue infection, when the MIC≤0.25 μg/mL, the PTA of 75 mg q12h and 100 mg q12h was greater than 90%, and the PTA of the three administration regimen was less than 90%, when the MIC≥0.5 μg/mL. CONCLUSION:The dose of 50 mg q12h is more suitable for the treatment of HAP, when MIC>0.5 μg/mL, tigecycline may need 100 mg q12h to obtain the best clinical efficacy in the treatment of cIAI. For cSSSI. when MIC≤0.25 μg/mL, tigecycline can be administered with 75 mg q12h and 100 mg q12h. For the three types of infections caused by Escherichia coli, the conventional dose of tigecycline may achieve clinical efficacy.

Evaluation of PET Mainstream Scattering Correction Methods / 中国医疗器械杂志

OBJECTIVE@#Current mainstream PET scattering correction methods are introduced and evaluated horizontally, and finally, the existing problems and development direction of scattering correction are discussed.@*METHODS@#Based on NeuWise Pro PET/CT products of Neusoft Medical System Co. Ltd. , the simulation experiment is carried out to evaluate the influence of radionuclide distribution out of FOV (field of view) on the scattering estimation accuracy of each method.@*RESULTS@#The scattering events produced by radionuclide out of FOV have an obvious impact on the spatial distribution of scattering, which should be considered in the model. The scattering estimation accuracy of Monte Carlo method is higher than single scatter simulation (SSS).@*CONCLUSIONS@#Clinically, if the activity of the adjacent parts out of the FOV is high, such as brain, liver, kidney and bladder, it is likely to lead to the deviation of scattering estimation. Considering the Monte Carlo scattering estimation of the distribution of radionuclide out of FOV, it's helpful to improve the accuracy of scattering distribution estimation.

Health risk assessment of chemical substances in drinking water in Shijiazhuang from 2014 to 2021 / 环境与职业医学

Background A variety of substances in drinking water are hazardous to human health and there are health risks associated with ingestion of these substances via drinking water. Objective To assess the carcinogenic and non-carcinogenic health risks of drinking water in Shijiazhuang from 2014 to 2021. Methods The collection, preservation, and testing of 10529 drinking water samples (including finished water and tap water) in Shijiazhuang were conducted from 2014 to 2021 and followed the Standard examination methods for drinking water (GB/T 5750—2006). The health risks of 15 chemicals in drinking water by oral exposure were assessed using the US Environmental Protection Agency's four-step method combined with Monte Carlo simulation. Results Among the 15 chemicals in drinking water assessed for their health risks at general exposure levels and high exposure levels via oral route in Shijiazhuang from 2014 to 2021, the leading three chemicals and related values of carcinogenic risks for adults were cadmium (1.11×10−4, 2.98×10−4), arsenic (5.88×10−5, 1.56×10−4), and chromium (5.48×10−5, 2.41×10−4), and the leading three chemicals and related values of non-carcinogenic risks were fluoride (3.57×10−1, 6.57×10−1), arsenic (1.31×10−1, 3.47×10−1), and nitrate (1.14×10−1, 5.98×10−1). The health risk values of trichloromethane and aluminum were elevated but still in acceptable ranges. Drinking water-associated health risk values were higher in males than in females, such as the cancer risk for general exposure levels of arsenic in men was 5.76×10−5, compared to 5.72×10−5 in women. The health risk values of cadmium, chromium, fluoride, nitrate, and other chemicals in ground water were higher than those of surface water, and the health risk values of trichloromethane and carbon tetrachloride were lower than those in surface water, such as the non-carcinogenic risk value for general exposure levels of fluoride in groundwater was 3.61×10−1, compared to 2.27×10−1 in surface water. Factors such as water transmission and distribution links, water period, and season affected the health risks of drinking water. The general exposure levels of trichloromethane in tap water had a higher carcinogenic risk of 1.75×10−7 compared with 8.17×10−8 in finished water. The general levels of arsenic exposure was higher in the dry season at 1.36×10−1, compared with 1.26×10−1 in the wet season. Conclusion Except that the carcinogenic risk of cadmium at general exposure levels in Shijiazhuang exceeds the maximum acceptable range recommended by US Environmental Protection Agency, the health risk values of the remaining 14 chemicals are below the maximum acceptable risk. The carcinogenic risk values of arsenic and chromium and the non-carcinogenic risk values of fluoride, arsenic, and nitrate are relatively high, but do not exceed the maximum acceptable ranges. The emphasis should be on the management of drinking water in highly exposed areas and populations.

Coarse-Grained Simulation of Amyloid Nucleation under Cooperative Effects of Peptides / 医用生物力学

Objective To explore the cooperative effect from β-propensity of amyloidogenic peptides on amyloid nucleation and its related products. Methods Based on a coarse-grained model for amyloidogenic peptides containing two states ( a soluble state and a β-sheet-forming state), with the consideration of two kinds of cooperative effects on β-propensity of peptides ( inhibiting and promoting the conformational conversion of peptides), the regulation of cooperative effects from amyloidogenic peptides on amyloid nucleation was analyzed through Monte Carlo simulations. Results In the case of the cooperative effect inhibiting the conformational conversion of peptides, amyloid nucleation occurred only within a certain interval of the peptide concentration, as well as inside the oligomers with certain sizes. Besides, the coexistence of on-pathway and off-pathway oligomers was observed. In the case of the cooperative effect promoting the conformational conversion of peptides, the β-sheet protofibril could be observed at physiological concentration as low as 4 μmol / L. Conclusions In this study, a more realistic coarse-grained model for amyloidogenic peptides was developed by introducing the cooperative effects of local concentration on β-propensity of amyloidogenic peptides, with observation of some intriguing phenomena not reported in previous simulations. The research findings not only improve current understandings about the mechanism of amyloid formation, but also provide theoretic references for the therapeutic strategies for curing neurodegenerative diseases

Monte Carlo simulation of α recoil migration of plutonium aerosol / 中国辐射卫生

Objective To evaluate the migration of plutonium aerosol caused by α recoil. Methods In this paper, the recoil deposition and Brownian motion of plutonium-containing nanoaerosols were simulated by Monte Carlo method. The recoil angle and the vertical first landing time of Brownian motion in the process of settling were sampled, and then the lateral displacements of Brownian motion were sampled to determine the final settling position of aerosol. Results For aerosols with particle sizes of 10-50 nm, the maximum migration distance of a single recoil settling was 1.39 μm. Brownian motion increased the migration capacity. Although there was a high likelihood that aerosols settled within 100 μm, there remained a slight probability of long-term suspension in the air. Conclusion The α recoil is one of the mechanisms of plutonium aerosol migration. An important mechanism for long-distance migration of nanoaerosols is that Brownian motion after recoil may cause them to suspend for a long time.

Monte Carlo simulation and analysis of eye lens dose of the first operator in interventional therapy / 中国辐射卫生

Objective To establish a model for estimating the eye lens dose of the first operator in interventional therapy based on the Monte Carlo simulation, and to provide a scientific basis for the rapid and accurate evaluation of the eye lens dose for radiation workers in interventional therapy. Methods Based on the MIRD phantom and eye model for adult Chinese males, the MCNPX program was used to establish the physical model to calculate the spatial distribution of radiation field and eye lens dose for the first operator. A GR200 Type A LiF (Mg, Cu, P) thermoluminescence dosimeter was used for experimental measurement to verify the simulation results. Results Monte Carlo simulation and experimental measurements showed that the spatial distribution of radiation field was symmetrical. Compared with the measured doses, the errors of the simulated eye lens dose of the first operator were between −8.3% and 7.3%. The dose of the left eye lens was higher than that of the right eye. Conclusion The Monte Carlo model constructed in this study initially realizes the simulation of eye lens dose of the first operator in interventional therapy. In the future, the model will be further optimized based on irradiation parameters such as exposure time, tube voltage, tube current, and projection direction used in clinic practice, so as to more accurately evaluate the eye lens dose of interventional therapy staff.

Development of a simplified phantom for calibration of whole-body counter / 中国辐射卫生

Objective To develop a simplified phantom for the calibration of whole-body counters. Methods A simplified phantom design method for the calibration of whole-body counters was established based on the process and method of calibrating whole-body counters. By using the established method and Monte Carlo method, a simplified phantom including the total body, thyroid, lungs, and gastrointestinal tract was designed to calibrate the ORTEC-Stand FAST II whole-body counter. The simplified phantom was compared with the BOMAB phantom through experimental measurements. Results Within the range of 50 keV to 2 MeV, for rays of the same energy in the same organ of the simplified phantom and BOMAB phantom, the simulated data of detection efficiency by whole-body counting showed an error within 5%, and the experimental measurements showed an error within 10%. Conclusion We developed a simplified phantom for the calibration of the whole-body counter, demonstrating the feasibility of using the simplified phantom instead of a physical body phantom for whole-body counter calibration, which can greatly facilitate whole-body counter calibration for internal radiation monitoring.

Model construction and software design of computed tomography radiation system based on visualization / 生物医学工程学杂志

The Monte Carlo N-Particle (MCNP) is often used to calculate the radiation dose during computed tomography (CT) scans. However, the physical calculation process of the model is complicated, the input file structure of the program is complex, and the three-dimensional (3D) display of the geometric model is not supported, so that the researchers cannot establish an accurate CT radiation system model, which affects the accuracy of the dose calculation results. Aiming at these two problems, this study designed a software that visualized CT modeling and automatically generated input files. In terms of model calculation, the theoretical basis was based on the integration of CT modeling improvement schemes of major researchers. For 3D model visualization, LabVIEW was used as the new development platform, constructive solid geometry (CSG) was used as the algorithm principle, and the introduction of editing of MCNP input files was used to visualize CT geometry modeling. Compared with a CT model established by a recent study, the root mean square error between the results simulated by this visual CT modeling software and the actual measurement was smaller. In conclusion, the proposed CT visualization modeling software can not only help researchers to obtain an accurate CT radiation system model, but also provide a new research idea for the geometric modeling visualization method of MCNP.