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Objective:To understand the radioactivity levels of water source in five key cities of Chengdu, Yibin, Mianyang, Guangyuan, Leshan in Sichuan province, and evaluate the radiation safety of these water sources.Methods:From 2016 to 2020, the measuring site selection, sampling and analysis were made for measuring the radioactivity levels of total alpha, total beta, 90Sr, 137Cs, 226Ra, U, Th in drinking water sources in these five cities. Reference was made, respectively, to the national standards Determination of total α radioactivity concentration in water thick source method (EJ/T 1075-1998), Determination of total β radioactivity in water evaporation method (EJ/T 900-1994), Radiochemical analysis method of strontium-90 in water and biological samples ash (HJ 815-2016), radiochemical analysis of cesium-137 in the ash of water and biological samples (HJ 816-2016), Analysis and determination of radium-226 in water (GB 11214-1989), Analysis of trace uranium in environmental samples -3 laser fluorescence law (HJ 840-2017), and Food safety in the test of radioactive substances in food determination of natural thorium and uranium (GB 14883.7-2016). Results:The activity concentration ranges from 0.011 to 0.076 Bq/L for total alpha, 0.027 to 0.098 Bq/L for total beta, 0.21 to 0.45 mBq/L for 137Cs, 1.0 to 2.4 mBq/L for 90Sr, 6.1 to 16.0 mBq/L for 226Ra, 0.06 to 0.21 μg/L for Th, and 0.73 to 3.30 μg/L for U. There were no significant differences in the concentrations of total alpha, total beta, 90Sr, 137Cs, 226Ra, U and Th in different water sources and different years ( P>0.05). There were no significant differences in the concentrations of total alpha, total beta, 90Sr, 137Cs and 226Ra during different water periods ( P>0.05). There were statistical differences in U activity concentration in different water periods ( H=16.53, P<0.05), and statistical differences in Th activity concentration in different water periods ( H=15.61, P<0.05). Conclusions:The survey showed that the total alpha, total beta, 90Sr, 137Cs, 226Ra, U and Th radioactivity levels in drinking water sources in Chengdu, Yibin, Mianyang, Guangyuan and Leshan of Sichuan province were at the same level as the relevant data in the Natural environmental radioactivity level in China published by the State Environmental Protection Bureau in 1995. All of there values were within the data range released by the 2013-2021 National Radiation Environment Monitoring Quality Report issued by the Radiation Environment Monitoring Technology Center of the Ministry of Ecology and Environment. The radioactivity level in water sources in the five key cities was at a safe level.
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Objective@#To study a method for verifying the doses to PTV and OAR as well as the 2D dose distribution arising from IMRT through using radiochromic films and TLDs.@*Methods@#Totally 7 medical electronic linear accelerators from Varian, Siemens and Elekta were selected. The polystyrene phantom provided by IAEA was conducted with CT scan. After irradiation with 6 MV X-rays, the TLDs and films were returned to the secondary standard dosimetry laboratory of China CDC for measurement and estimation.@*Results@#According to the IAEA requirements, the relative deviations between TLD-measured and TPS-planned values for PTV and OAR doses were both within ±7.0%. For PTV, the measured relative deviations for 5 accelerators were in the range of -4.0% to 3.4%, consistent with the IAEA requirements, whereas the values for the other 2 accelerators were in the range of -7.0% to 10.6%, not consistent with the requirements. For OAR, the values for 4 accelerators were in the range of -5.6% to 3.3%, consistent with the IAEA requirements, whereas the values for the other 3 accelerators were in the range of -20.8% to 11.5%, not meeting the requirements. As required by the IAEA, the 2D dose distribution 3 mm/3% pass rate should be higher than 90%. The measured values for 5 accelerators were in the range of 91.8% to 98.5%, consistent with the requirements, whereas the values measured for the other 2 were 45.0% and 77.0% respectively, not meeting the requirements.@*Conclusions@#It is feasible for using TLDs and radiochromic films to verify the doses to PTV and OAR and the 2D dose distribution in IMRT. This method should be applied to not only quality verification but also hospital internal audit to the extent possible.
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Objective To study a method for verifying the doses to PTV and OAR as well as the 2D dose distribution arising from IMRT through using radiochromic films and TLDs.Methods Totally 7 medical electronic linear accelerators from Varian,Siemens and Elekta were selected.The polystyrene phantom provided by IAEA was conducted with CT scan.After irradiation with 6 MV X-rays,the TLDs and films were returned to the secondary standard dosimetry laboratory of China CDC for measurement and estimation.Results According to the IAEA requirements,the relative deviations between TLD-measured and TPS-planned values for PTV and OAR doses were both within ±7.0％.For PTV,the measured relative deviations for 5 accelerators were in the range of-4.0％ to 3.4％,consistent with the IAEA requirements,whereas the values for the other 2 accelerators were in the range of-7.0％ to 10.6％,not consistent with the requirements.For OAR,the values for 4 accelerators were in the range of-5.6％ to 3.3％,consistent with the IAEA requirements,whereas the values for the other 3 accelerators were in the range of-20.8％ to 11.5％,not meeting the requirements.As required by the IAEA,the 2D dose distribution 3 mm/3％ pass rate should be higher than 90％.The measured values for 5 accelerators were in the range of 91.8％ to 98.5％,consistent with the requirements,whereas the values measured for the other 2 were 45.0％ and 77.0％ respectively,not meeting the requirements.Conclusions It is feasible for using TLDs and radiochromic films to verify the doses to PTV and OAR and the 2D dose distribution in IMRT.This method should be applied to not only quality verification but also hospital internal audit to the extent possible.
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Objective To verify the accuracy of multi-leave collimators (MLC) leaves position in intensity modulated radiation therapy (IMRT) using radiochromic films.Methods 7 medical electronic linear accelerators of Varian,Elekta or Siemens design were chosen.25 cm× 25 cm films were put on 30 cm×30 cm×3.0 cm homogeneous solid phantom and covered with a 2.0 cm thick of homogeneous solid phantom.The CT scanned images were transmitted to TPS for plan preparation.A 5 strip picket fence pattern was formed by MLC leaf,each 3 cm long and 0.6 cm wide,with 3.0 cm wide strip separation.At the maximum dose point,the SSD was 100 cm,with 250 MU per strip.After exposure,the films were transmitted to the dosimetry laboratory at IAEA for measurement and calculation.Results For 6 of 7 accelerators chosen,the differences of film-measured and TPS-planned MLC leaf position for every fence were within ± 0.5 mm as required by IAEA,and the other one not consistent with the requirements.The difference of film-measured MLC leaf position between each pair and all pair for 7 accelerators were within ± 0.5 mm,in line with IAEA's requirements.The differences of film-measured MLC leaf actual width were within 0.75 mm,as required by IAEA,for 6 accelerators and-0.8 mm for the other one,not consistent with the IAEA requirements.The standard deviations of film-measured MLC leaf actual width for all pairs for 6 accelerators were ＜0.3 mm,in line with IAEA requirements,but 0.4 mm for the other one,not consistent with IAEA requirements.Conclusions It is simple,fast and accurate to use radiochromic films for verification of the accuracy of MLC leaf position in IMRT.Therefore it is advisable to widely use radiochromic films in IMRT clinical practice.
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Objective To measure absorbed dose and verify two-dimensional dose distribution from IMRT MLC using thermoluminescence dosimeters (TLDs) and films.Methods The teflon phantom was scanned by CT and its images were transmitted to TPS for planning.The 6 Gy-corresponding MUs were calculated at 90 cm SSD and 10 cm depth and on 5 cm × 5 cm radiation field.All the plans were implemented at 7 medical linear accelerators,which were produced by Varian,Elekta and Siemens and selected from 7 third-grade first-class hospitals according to the technical conditions of various regions in Sichuan province.The homogeneous solid phantoms used in hospitals were covered by 30 cm × 30 cm and 25 cm × 25 cm films.Then,the films were covered by thicker-than-20 cm phantoms.Finally,the plans were implemented by aligning the center of beams to the films center.Results The relative deviations of the measured absorbed dose to TPS-planned dose were 1.4％,3.7％,-2.5％,-0.3％,4.9％,4.9％,5.0％ for TLDs and 4.7％,4.3％,1.5％,3.9％,-1.6％,3.3％,-1.3％ for films,respectively,all consistent with the limit of less than 5％.The passing rates of 2D dose distribution (3 mm/3％) were 99.9％,98.5％,98.5％,97.9％ and 70.0％ for 5 accelerators,with only one not consistent with the requirements.Conclusions It is convenient to measure the absorbed dose to photon beam field and verify two-dimensional dose distribution using TLDs and films,which can provide quality assurance for radiation treatment plans.
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Melamine is a kind of triazine compound and the fluorescence of it can get enhanced in the presence of cationic surfactant in weak alkaline medium. A new fluorescent spectrophotometry based on this principle) has been developed to determine melamine under the optimum conditions such as Tris-HCl buffer solution), pH 8.0 and with CTMAB as sensitizing agent. The linear range, detection limit and relative standard deviation were 25-1000 μg/L, 19 μg/L and 1.6%,respectively. The samples were pretreated according to the solid phase extraction monolithic column to carry out the detection of real milk. This method is simple, rapid and accurate. It can be used to screen and detect the milk samples primarily.