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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.
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Objective To explore the effect of low dose ionizing radiation on the thyroid of radiation workers in our country. Methods The literatures were searched of domestic and foreign journals from 1996 to 2017. A total of 15 studies involving 6332 participants were included. These studies were screened according to the inclusion and exclusion criteria. Three indicators of the thyroid function were analyzed in radiation workers, including triiodothyronine ( T3 ) , thyroxine ( T4 ) and thyroid stimulating hormone( TSH) . The Meta analysis was performed using Stata 14. 0 software. Results For radiation workers, the standardized mean difference (SMD) of T3 levels was -0. 32[95% CI ( -0. 61,-0. 04), P=0. 03?, lower than that of the control group. Univariate meta - regression analysis of sources of heterogeneity showed that only gender composition was related to heterogeneity of the study [ adjusted R-squared (Adj R2 ) =29. 99%, P =0. 03]. The SMD of T4 levels was -0. 49 [95%CI ( -0. 94,-0. 03), P=0. 04], lower than that of the control group. Only the gender composition was related to heterogeneity of the study[Adj R2 =26. 60%, P=0. 02]. However, the SMD of TSH levels was 1. 10 [95% CI (0. 32,1. 89), P=0. 006], higher than that of the control group. Conclusions The long term exposure of radiation workers to low dose ionizing radiation may lead to negative impact on thyroid. It is important to strengthen radiation protection of thyroid.
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Objective To explore the effect of low dose ionizing radiation on the thyroid of radiation workers in our country. Methods The literatures were searched of domestic and foreign journals from 1996 to 2017. A total of 15 studies involving 6332 participants were included. These studies were screened according to the inclusion and exclusion criteria. Three indicators of the thyroid function were analyzed in radiation workers, including triiodothyronine ( T3 ) , thyroxine ( T4 ) and thyroid stimulating hormone( TSH) . The Meta analysis was performed using Stata 14. 0 software. Results For radiation workers, the standardized mean difference (SMD) of T3 levels was -0. 32[95% CI ( -0. 61,-0. 04), P=0. 03?, lower than that of the control group. Univariate meta - regression analysis of sources of heterogeneity showed that only gender composition was related to heterogeneity of the study [ adjusted R-squared (Adj R2 ) =29. 99%, P =0. 03]. The SMD of T4 levels was -0. 49 [95%CI ( -0. 94,-0. 03), P=0. 04], lower than that of the control group. Only the gender composition was related to heterogeneity of the study[Adj R2 =26. 60%, P=0. 02]. However, the SMD of TSH levels was 1. 10 [95% CI (0. 32,1. 89), P=0. 006], higher than that of the control group. Conclusions The long term exposure of radiation workers to low dose ionizing radiation may lead to negative impact on thyroid. It is important to strengthen radiation protection of thyroid.
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<p><b>OBJECTIVE</b>To investigate the variable number tandem repeats (VNTR) genetic polymorphisms, genotyping and distribution pattern of clinical Mycobacterium (M.) tuberculosis isolates from Qinghai province.</p><p><b>METHODS</b>The clinical M. tuberculosis strains isolated from the patients with tuberculosis and related background data were collected from Qinghai Provincial Center for Disease Control and Prevention from 2009 to 2012. Genotyping was conducted by using multiple locus VNTR analysis (MLVA). Genomic DNA was extracted and 15 VNTR loci were amplified with PCR and the PCR products were detected with gel electrophoresis. The VNTR diversity and clusters of genotyping were analyzed with BioNumerics (Version 5.0).</p><p><b>RESULTS</b>A total of 251 clinical M. tuberculosis isolates were analyzed with 15 VNTR loci showing that there were great genetic diversity in these isolates. Six of the 15 VNTR loci, showed that the Hunter-Gaston index (HGI) were higher than 0.6, in which the highest resolution was MIRU26. The clusters of genotyping showed that these isolates could be categorized into four gene clusters and 238 genotypes. The four gene clusters accounted for 4.9%, 91.9%, 1.6% and 1.6% of the clinical isolates, respectively.</p><p><b>CONCLUSION</b>The results showed that there is great variety of VNTR genetic polymorphisms in clinical M. tuberculosis isolates in Qinghai province.</p>