Monte Carlo calculation of neutron doses to organs of a female undergoing a pelvic 18 MV irradiation

Applying of high-energy photon beams beside all advantages obstacled by photoneutrons that may cause extra dose to the patient that has not been considered in routine radiotherapy. The purpose of this study is calculation of neutron and gamma doses to a female undergoing a pelvic 18 MV irradiation. A simplified Linac head model as a sphere with 10 cm radius of tungsten and with the total spectrum of an isotropic neutron distribution was located inside a typical bunker. The female anthropomorphic phantom was irradiated with equal weighted four-field pelvic box (18MV). MCNPX (2.4.0) code was used to calculate of absorbed doses. The greatest effective dose, 1.04 mSv Gy-1, was calculated for the AP field while the lowest effective dose, 0.36 mSv Gy-1, was obtained for the RL field. The Percent risk of fatal second malignancy of neutron contamination following a 70 Gy x-ray treatment dose (with equal weights for each field, 17.5 Gy) is 0.152 , including 0.056 for the AP field, 0.033 for the PA field, 0.031 for the RL field and 0.032 for the LL field. If this dose delivered only with the AP field, the risk would be 0.224 , which is 32 higher than that is in case of 4-field irradiation. Our present analysis shows that this simplified model can be used to estimating of photoneutron doses

The effects of backscattered radiation into beam monitor chamber: Study of 6 and 18 MV conventional and removed flattening filter clinical accelerator

In some linear accelerators (Linac), the collected charges in beam monitor chamber (BMC) is partly caused by the backscattered particles from the accelerator components downstream the BMC that influence the Linac output factors. In the intensity modulated radiation therapy technique, the desired dose distribution can be achieved through an unflattened beam. Although removing the flattening filter provides some advantages, the amount of backscatter radiation into BMC can be changed. In this study, contribution of backscattered particles into the BMC response of a Varian 2300 C/D Linac with and without a flattening filter was determined for 6, 18 MV photon beams. The experimental procedure included telescopic method and calculation procedure consisted of Monte Carlo simulation (MCNPX, version 2.4.0), were used to investigate the contribution of backscattered particles into the BMC performance. Our results showed a 2.3 and 3 increase in backscatter for a 0.5 � 0.5 cm2 field compared to a 40 � 40 cm2 field for 6 MV and 18 M V, respectively. The energy deposition from backscattered radiation is mainly caused by backscattered electrons. Removing the flattening filter did not change the BMC performance for a conventional Linac with a flattening filter. However, this result was not valid for small fields (e.g. 0.5 � 0.5 cm2, 18 MV). The corrected backscatter factors is necessary to taking into account the contribution of backscattered radiation in the monitor chamber response for small fields in the case of the free flattening filter Linacs (18 MV)

High-dose-rate 192Ir brachytherapy dose verification: A phantom study

Background: The high-dose-rate (HDR) brachytherapy might be an effective tool for palliation of dysphagia. Because of some concerns about adverse effects due to absorbed radiation dose, it is important to estimate absorbed dose in risky organs during this treatment. Objectives: This study aimed to measure the absorbed dose in the parotid, thyroid, and submandibular gland, eye, trachea, spinal cord, and manubrium of sternum in brachytherapy in an anthropomorphic phantom. Materials and Methods: To measure radiation dose, eye, parotid, thyroid, and submandibular gland, spine, and sternum, an anthropomorphic phantom was considered with applicators to set thermoluminescence dosimeters (TLDs). A specific target volume of about 23 cm3 in the upper thoracic esophagus was considered as target, and phantom planned computed tomography (CT) for HDR brachytherapy, then with a micro-Selectron HDR (192Ir) remote after-loading unit. Results: Absorbed doses were measured with calibrated TLDs and were expressed in centi-Gray (cGy). In regions far from target (� 16 cm) such as submandibular, parotid and thyroid glands, mean measured dose ranged from 1.65 to 5.5 cGy. In closer regions (� 16 cm), the absorbed dose might be as high as 113 cGy. Conclusions: Our study showed similar depth and surface doses; in closer regions, the surface and depth doses differed significantly due to the role of primary radiation that had imposed a high-dose gradient and difference between the plan and measurement, which was more severe because of simplifications in tissue inhomogeneity, considered in TPS relative to phantom. © 2015, Iranian Journal of Cancer Prevention

Different patterns of association between education and wealth with non-fatal myocardial infarction in Tehran, Iran: A population-based case-control study

Background: Myocardial Infarction (MI) is a main cause of death and disability worldwide, which involves a number of genetic, physiopathologic and socio-economic determinants. The aim of this study was to assess the patterns of association between education, wealth and some other risk factors with non-fatal MI in Tehran population. Methods: Data derived from a second round of large cross-sectional study, Urban HEART-2, conducted in Tehran in 2011. Out of 118542 participants, all 249 self-reported incident cases of nonfatal MI were selected as the case group. A number of 996, matched on age and sex, were selected as controls. Principle component analysis (PCA) was used to calculate wealth index and logistic regression model to assess relations between the study variables. Results: Mean (SD) age of participants was 60.25 (12.26) years. A total of 870 (69.9) of the study subjects were men. Education, wealth status, family violence, hypertension and diabetes were observed as independent predictors of non-fatal MI. Overall, as the level of education increased, the odds of non-fatal MI decreased (p<0.001). We observed an almost J-shaped association between wealth status and non-fatal MI. No significant associations were found between marital status, BMI and current smoking with non-fatal MI (p<0.05). Conclusion: We found different patterns of association between education and wealth with nonfatal MI among Tehran adults. Lower risk of non-fatal MI is linked to high educated groups whereas economically moderate group has the lowest risk of non-fatal MI occurrence

The influence of using different reconstruction algorithms on sensitivity of quantitative 18F-FDG-PET volumetric measures to background activity variation

Introduction: This study aims to investigate the influence of background activity variation on image quantification in differently reconstructed PET/CT images. Methods: Measurements were performed on a Discovery-690 PET/CT scanner using a custom-built NEMA-like phantom. A background activity level of 5.3 and 2.6 kBq/ml 18F-FDG were applied. Images were reconstructed employing four different reconstruction algorithms: HD (OSEM with no PSF or TOF), PSF only, TOF only, and TOFPSF, with Gaussian filters of 3 and 6.4 mm in FWHM. SUVmax and SUVpeak were obtained and used as cut-off thresholding; Metabolic Tumor Volume (MTV) and Total Lesion Glycolysis (TLG) were measured. The volume recovery coefficients (VRCs), the relative percent error (�MTV), and Dice similarity coefficient were assessed with respect to true values. Results: SUVmax and SUVpeak decreased and MTV increased as function of increasing the background dose. The most differences occur in smaller volumes with 3-mm filter; Non-TOF and Non-PSF reconstruction methods were more sensitive to increasing the background activity in the smaller and larger volumes, respectively. The TLG values were affected in the small lesions (decrease up to 12). In a range of target volumes, differences between the mean �MTV in the high and low background dose varied from -11.8 to 7.2 using SUVmax and from 2.1 to 7.6 using SUVpeak inter reconstruction methods. Conclusion: The effect of the background activity variation on SUV-based quantification in small lesion was more noticeable than large lesion. The HD and TOFPSF algorithms had the lowest and the highest sensitivity to background activity, respectively. © 2018 Iranian Journal of Nuclear Medicine. All Rights Reserved

Diagnostic accuracy of dual-source computerized tomography coronary angiography in symptomatic patients presenting to a referral cardiovascular center during daily clinical practice

Background: There are numerous studies that address the diagnostic value of dual-source computed tomography (DSCT) as an alternative to conventional coronary angiography (CCA). However, the benefit of application of DSCT in a real world clinical setting should be evaluated. Objectives: To determine the diagnostic accuracy of DSCT technique compared with CCA as the gold standard method in detection of coronary artery stenosis among symptomatic patients who are presented to a referral cardiovascular center during daily clinical practice. Patients and Methods: Evaluating the medical records of a tertiary care referral cardiovascular center, 47 patients who had undergone DSCT and CCA, and also met the inclusion and exclusion criteria of the study were selected. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and likelihood ratios (LRs) of the DSCT imaging technique were calculated. Results: In total, 97.8 of the segments (628/642) could be visualized with diagnostic image quality via DSCT coronary angiography. The mean heart rate during DSCT was 69.2±12.2 bpm (range: 39 - 83 bpm), and the mean Agatston score was 507.7±590.5 (range: 0 - 2328). Per segment analysis of the findings revealed that the sensitivity, specificity, PPV, NPV, positive LR (PLR) and negative LR (NLR) of DSCT technique for evaluation of patients with coronary artery disease were 93.7, 96.8, 92.7, 97.2, 29.4, and 0.066, respectively. Also per vessel, analysis of the findings showed a sensitivity of 97.1, a specificity of 94.0, PPV of 95.3, NPV of 96.3, PLR of 16.1, and NLR of 0.030. Conclusion: Our results indicate that DSCT coronary angiography provides high diagnostic accuracy for the evaluation of CAD patients during daily routine practice of a referral cardiovascular setting. © 2016, Tehran University of Medical Sciences and Iranian Society of Radiology

A full quantitative analysis of 18 MV photon beam from 2100 C/D-Varian clinical linear accelerator with and without flattening filter

Background: During intensity modulated radiation therapy (IMRT) technique, theoretically, presence of flattening filter (FF) across the beamline of clinical linear accelerator (linac) is not essential to obtain uniform lateral profiles due to intensity modulation of photon beams by multileaf collimators (MLCs). The aim of this study was to investigate the dosimetrical properties of 18 MV photon beam-Varian linac with and without FF. Materials and Methods: All dose measurements were performed on 18 MV, FF mode-Varian 2100C/D linac. The FF and flattening filter free (FFF) modes of linac were modeled by MCNPX 2.4. code. The photon and contaminant electrons spectra, dose rate, present depth doses (PDD), lateral dose profiles, total and collimator scatter factors and out of field doses were calculated and compared with and without FF. Results: Removing the FF increased the photon and contaminant electron fluences by factors of 5.48 and 3.94 for a 5 � 5 cm2 field size, respectively. The surface dose increased up to 155. The flatness of dose profile was disturbed and deteriorated with increase of field size. Despite the dependence of the total scattering factor on field size, the variation of collimator scattering factors was neglected. The out-of-field dose decreased about 81.5 for a 5 � 5 cm2 field size. Conclusion: Removing FF from the linac head increases the dose rate and decreases the out-of-field dose, but the increased skin dose and deteriorated flatness of lateral dose profile are the main disadvantages of the FFF mode. © 2019 Novin Medical Radiation Institute. All rights reserved

Monte carlo estimation of electron contamination in a 18 MV clinical photon beam

Background: The electron contamination may reduce or even diminish the skin sparing property of the megavoltage beam. The detailed characteristics of contaminant electrons are presented for different field sizes and cases. Materials and Methods: The Monte Carlo code, MCNPX, has been used to simulate 18 MV photon beam from a Varian Linac-2300 accelerator. All dose measurements were carried out using a PTW-MP2 scanner with an ionization chamber (0.6 CC) at the water phantom. Results: The maximum electron contaminant dose at the surface ranged from 6.1 for 5 � 5 cm2 to 38.8 for 40 � 40 cm2 and at the depth of maximum dose was 0.9 up to 5.77 for the 5 � 5 cm2 to the 40 � 40 cm2 field sizes, respectively. The additional contaminant electron dose at the surface for the field with tray increased 2.3 for 10 � 10 cm2, 7.3 for 20 � 20 cm2, and 21.4 for 40 � 40 cm2 field size comparing to the standard field without any accessories. This increase for field with tray and shaping block was 5.3 and 13.3 for 10 � 10 and 20 � 20 cm2, respectively, while, the electron contamination decreased for the fields with wedge, i.e. 2.2 for the 10 � 10 cm2 field. Conclusion: The results have provided more comprehensive knowledge of the high-energy clinical beams and may be useful to develop the accurate treatment planning systems capable of taking the electron contamination in to account

Applying a basic development needs approach for sustainable and integrated community development in less-developed areas: Report of ongoing Iranian experience

Introduction: Despite considerable achievements in the provision of basic developmental facilities in terms of drinking water, access to primary healthcare services, high-quality and nutritious food, social services, and proper housing facilities, there are many rural and slum communities in Iran where these essential needs remain unfulfilled. Lack of equity is prominent, as large differences exist in underprivileged provinces. New policies developed in the past two decades have resulted in substantial achievements in meeting population needs and reducing the socio-economic gap; nevertheless, poverty levels, unemployment due to a large increase in the birth rate in the early 1980s, and lack of community participation are matters yet to be addressed. To overcome these deficiencies, a basic development needs approach was adopted to promote the concept of community self-help and self-reliance through intersectoral collaboration, creating an environment where people could take an active part in the development process, with the Iranian government providing the necessary support to achieve the desired level of development. Description of the project: Following firm commitment from the Iranian government and technical support from the World Health Organization Regional Office, basic development needs was assigned a high priority in health and health-related sectors, reflected in the third National Masterplan (2001-2005). A comprehensive intersectoral plan was designed, and pilot projects were commenced in three villages. Each village elected a representative, and committee clusters were formed to run and monitor projects identified by a process of local needs assessment and priority assignment. In each region, a variety of needs were elicited from these assessments, which were actively supported by local authorities. Lesson learned: A basic development needs approach was found to be a reliable discipline to improve community participation, needs-led resource allocation and intersectoral co-operation in community development, particularly in underprivileged areas. Iran's initial experience of basic development needs has gained widespread public support but will require periodical evaluation as it is introduced into other rural and urban regions across the country. © 2004 The Royal Institute of Public Health. Published by Elsevier Ltd. All rights reserved

Preliminary report of a nationwide case-control study for identifying risk factors of tuberculosis following renal transplantation

Background. Tuberculosis (TB) is an important infection encountered posttransplantation, especially among patients in developing countries, where there are high incidences of morbidity and mortality. Materials and Methods. One hundred and twenty subjects (1) from 15 major kidney transplantation centers in Iran from 1984 to 2003 were compared with 440 controls who were matched for operative time, treatment center, and surgical team. Results. Mean ages of research subjects and controls were 38.6 and 36.6 years (P = .04), respectively. The mean duration of pretransplantation hemodialysis was 29 months (range, 2 to 192 months) in research subjects and 20 months (range, 1 to 180 months) in controls (P = .003). Positive past history of tuberculosis was detected in 4 (3.3) research subjects and in 7 (1.5) controls (P = .2). Fifty-two research subjects (43.3) and 241 controls (54.8) had pretransplantation purified protein derivative of tuberculin less than 5 mm (P = .02). Mean dosages of initial and maintenance immunosuppressive drugs in research subjects and in controls were not significantly different. Sixty research subjects (50) and 152 controls (34.5) had rejection prior to diagnosis of TB (P = .03). Conclusion. To our knowledge, this is the first study that demonstrates an increased risk of posttransplant TB by prolonged duration of pretransplant hemodialysis and number of posttransplant rejection episodes. Further study is needed to clarify these findings specifically with respect to various immunosuppressive regimens. © 2005 by Elsevier Inc. All rights reserved