Objective To understand the functional status and radiation protection requirements of helical tomotherapy (TOMO) unit when it is applied in clinic treatment so as to promote the construction of TOMO quality control system.Methods A helical tomotherapy unit with a type of tomotherapy Hi-Art was employed as the radiotherapy unit.A series of tests and analyses on dosimetric and radiation safety performance parameters of the TOMO unit were conducted with the use of a A1SL ionization chamber,a set of solid water equivalent phantoms and other test equipments.The performance parameters were compared with that of a conventional 6 MV accelerator with a type of ARTISTE.Results The deviations of static and dynamic output dose were-1.51％ and 1.18％,respectively.The values of PDD10/PDD1.5 and PDD20/PDD1.5 were 0.608 and 0.318 within the range of X-ray quality parameters calibration.Under the different field conditions of 40 cm × 5 cm,40 cm × 2.5 cm and 40 cm × 1 cm,the stability of transverse/longitudinal dose distribution curve was no more than 1.20％ and the offset distance of Jaw width was smaller than 0.5 mm.Radiation leakage ratio of the treatment rotating center from the muhileaf collimator (MLC) was 0.20％.No matter the average or the maximum value of the leakage radiation from couch plane was less than 0.02％.Conclusions The performances and testing requirements of TOMO unit are different from a conventional electron linear accelerator,the quality control index of TOMO unit should be set seperately and tested strictly in terms of the specific requirements of the unit by complying with the QC programme.The reliable quality control system should be established and effectively implemented to serve the radiotherapy quality and radiation safety effectively in the tomotherapy.

Objective To study the radiation dose level and dose distribution of leakage and scattering radiation in a helical tomotherapy (TOMO) room,and to identify the dose distribution characteristic which is different from the conventional radiotherapy so as to provide scientific data for the radiation protection of TOMO.Methods A helical tomotherapy facility typed Tomotherapy Hi-Art was employed as the radiotherapy device.The air kerma from leakage radiation and scattering radiation distributed on the couch plane and in TOMO room were detected mainly by GR-200A TLDs of LiF(Mg,Cu,P),while 100 Gy were being accumulated under the condition of simulation radiation treatment.Then,the leakage radiation ratio and scattering-leakage radiation ratio (the ratio of site radiation dose to isocenter standard output dose) were calculated.Results The radiation level and dose distribution of leakage radiation and scattering radiation in the TOMO treatment room were in bilateral symmetry to the rotation isocenter and the treatment couch longitudinal axis,and the radiation level in front of the radiotherapy device was significantly higher than that of the rear of the TOMO equipment.In the plane of treatment couch,the maximum leakage radiation ratio at the position 100 cm away from the isocenter was only 1.3 × 10-4,and the mean value of the leakage radiation ratio at the position 300 cm away from the isocenter was lower than 2.0 × 10-5.The scattering radiation at 200-300 cm away from the isocenter was accounted for 25％-30％ of the leakage radiation from the responding sites,and the indoor scattering radiation decreased faster than leakage radiation with the distance from the isocenter.Conclusions The radiation level of leakage and scattering in a TOMO room is significantly lower than that in a conventional radiotherapy room.

Objective To assess the level of radiation exposures of operators in three typical types of interventional fluoroscopic procedures.Methods Alderson Radiation Therapy (ART) phantom was used to stimulate the practices of diagnosis and therapy using TLDs for dose measurement.The radiation exposures of eye lens, neck, and breast were measured when the lead shielding of machine was on/off and the equivalent dose and effective dose to the eye lens were estimated.Results Radiation exposure of head was obviously reduced by 85% -90% when the lead shielding was on.The doses in different procedures were different.In cerebral angiography the dose equivalent of eye len was the highest in the three procedures.The annual effective dose for the operators was smaller in peripheral vascular interventions than that in cardiovascular interventional therapy and that in cerebral angiography.Conclusions The operators involved in intervention will receive an annual effective dose of less than 20 mSv as recommended by the ICRP under the protection conditions provided by the current study, except for eye lens.Attention should be paid to the protection of the eyes of operators.

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Objective To investigate the radiation dose levels to the adults examined from diagnostic exposure in Beijing. Methods The radiation doses to the examined individuals were measured by using individual diagnostic radiology equipments in 30 random hospitals from a total of 10 districts and suburban areas, including 1 182 samples of X-ray photography,542 samples of mammography and 410 samples of CT examination. Results 2 134 samples were measured in this study. The dose ranges of X-ray photography, CR, and DR were 0?4 -24?1, 0?3 -13?9 and 0?1 -15?9 mGy, respectively. The average dose range of glandular breast was 0?3-5?4 mGy. In 410 CT samples the value of CTDIw , CTDIvol and DLP were 28?1 - 96?3 mGy, 7?0 - 23?4 mGy, and 162?2 - 898?1 mGy·cm, respectively. Conclusions Several dose levels from diagnostic examination were higher than guidance level for medical exposure in GB 18871-2002,which should be noted.

Objective:To explore the present state of radiation protection in an operational large-sized irradiation facility and the distribution of incurred radiation doses in the controlled area under abnormal conditions, and to analyze the acompanied radiation risk.Methods:With an irradiation facility in operation as the research object, the radiation doses were measured using AT1121 X and gamma dose rate meters for the soruce both in working and storage. Thermoluminescent dosimeters (TLDs) were used to measure the dose distribution in an irradiation field under abnormal conditions. The radiation safety features were checked against the several relevant national standards, with the radiation risks evaluated.Results:The radiation dose rates were in the range of 0.09-0.11 μSv/h, lower than the environmental background level whether in storage or working. Under abnormal working conditions, the radiation dose values from high to low were 1.0-101.3 Sv, 32.7-514.0 mSv and 8.7-183.2 μSv in the irradiation field, respectively. At the outside maze, the doses were close to the background level.Conclusions:The protection features of the irradiation facility meet the requirements of the relevant national standards. Under abnormal conditions, radiation could cause serious damages to the persons staying in the irradiation field. These persons were suggested to access to maze as soon as possible to reduce the exposure time, and activate the emergency protection equipments to deescalate the 60Co source onto the well.

Objective:To compare the calculation result and analyzes the reasons for their differences so as to provide reference for the revision and improvement of the current national standards on radiation shielding design for the room of brachytherapy.Methods:For the initial activity 10 Ci (1 Ci=3.7×10 10 Bq) of radioactive sources, the shielding schemes of brachytherapy room were designed in accordance with UK Institnte of Physics and Engineering in Medicine(IPEM) Report 75, USA NCRP Report 151 and the national standard GBZ/T 201.3-2014, respectively. The differences in shielding limits, occupancy factors and other relevant factors are compared in detail. Results:The annual exposure time in a typical brachytherpy room was about 330 h. The point-specific concrete thickness were 70, 65, 61, 70, 50 cm as required by NCRP Report 151, 41, 43, 30, 40, 39 cm by IREM regulations and 84, 79, 46, 88, 39 cm by GBZ/T 201.3, respectively. The concerned concrete shielding thickness calculated under the GBZ/T 201.3-2014 was generally thicker, with lesser difference from NCRP Report 151 result, whereas that from the IPEM75 report was thinnest. The equivalent lead shielding thicknesses of the protective doors calculated using the three method are 1.170, 0.854 and 1.040 cm, respectively.Conclusions:The shielding thickness calculated using the calculation method and evaluation index recommended by the current Chinese shielding standards for brachytherapy bunker is similar to that reported in NCRP151, but is conservative. In particular, the evaluation index of instantaneous dose equivalent rate required by the current national standards and the relative conservative value of occupancy factor will significantly increase the shielding thickness required by the main shielding area.

Objective: To investigate the implementation of GBZ/T 201.3-2014 Radiation Shielding Specification for Radiotherapy Room--Part 3: Radiotherapy Room of γ-ray Sources (hereinafter referred to GBZ/T 201.3-2014). Methods: A total of 129 personnels, who were involved in the approval and supervision of radiation diagnosis and treatment construction projects in 19 provincial administrative agencies, engaged in radiation protection testing and evaluation of γ-ray radiotherapy rooms in radiation health technology service institutions, and used GBZ/T 201.3-2014 in other institutions (environmental impact assessment, education and scientific research), were selected as the participants using a stratified random sampling method. A questionnaire survey was conducted to assess their awareness and application of the standard. Results: The participants' awareness of GBZ/T 201.3-2014 was ≥63.6%, but the training rate was only 9.1% to 50.0%. The familiarity with the various chapters of the standard was over 86.4%. And 42.6% of the participants reported using the standard at least once a year. Regarding the applicability of the standard, all of the participants believed that the standard meets the needs of approval, supervision, testing, or evaluation, and adapts to the updated development of radiotherapy equipment and technology. And 94.6% of the participants believed that the use of the standard could improve the level of protection design and management, and 92.2% believed that the standard was widely applied. Regarding the adequacy of the standard, 97.7% of the participants believed that the standard's reference for ambient dose equivalent rate was reasonable, while 34.1% believed that the standard needs revision. Conclusion: The participants are satisfied with the standard and believe its applicability. They have a good level of awareness of the standard, but there is a room for improvement in their familiarity with the shielding calculation related content of the standard. The promotion, training, and practicality of the standard need to be strengthened.

Objective To analyze the performance differences of CT scanners with different detector rows between different manufacturers,and to provide the basis for the rational allocation and use of these CT scanners.Methods According to the result from the sentinel surveillance in 2014,a total of 148 medical institutions were equipped with CT scanners in 16 districts of Beijing,including general hospital(53),cancer hospital(5),TCM hospitals(25),children′s hospitals(2),community hospitals(30)and other specialized medical institutions(33).According to the principle of simple random sampling,40 medical institutions are selected,including 14 general hospitals,1 cancer hospital,7 Chinese medicine hospitals,1 children′s hospital,8 community hospitals and 9 other specialized medical institutions.A total of 141 CT scanners are selected from all CT sets of the selected medical institutions from 2012 to 2014.According to GB 17589-2011 X-ray computed tomography device quality assurance testing status test,four parameters related closely to image quality were tested,including CT value(water),noise,high contrast resolution,and low contrast detectability.Results No significant differences were found in CT value(water),noise and low contrast detectability among CT scanners produced by different manufacturers(P＞0.05),whereas high contrast resolution was found to have a remarkable difference(χ2＝34.706,P＜0.05).Significant differences were found in noise,high contrast resolution and low resolution detectability between the CT scanners with ＜64 detector rows and ≥64 detector rows(χ2＝6.978,10.040,15.973,P＜0.05).However,there is no difference in CT value(water)(P＞0.05).For less-than-64 detector row CT scanners,no significant difference was found in CT value(water),noise and low contrast detectability among different manufacturers(P＞0.05).only high contrast resolution differed remarkably(χ2＝9.941,P＜0.05).For more-than-or equal-to-64 detector row CT scanners,CT value(water)and noise have no differences among different manufacturers(P ＞0.05),whereas,there were significant difference in high contrast resolution and low contrast detectability(χ2＝31.376,32.967,P＜0.05).Conclusions There were a few differences in the performance testing of CT scanners from different manufacturers,and the less-than-64 detector row CT scanners have advantages in noise and low contrast detectability compared with the more-than-64 detector row CT scanners,whereas the latter have advantages in high contrast resolution and scanning time,allowing its wider application in medical institutions with more special diseases.

Objective:To monitor and analyze the activity concentrations of 7Be and 210Pb in atmospheric aerosol in Beijing from 2017 to 2020. Methods:Totally 1 074 atmospheric aerosol samples were collected by high flow air sampler (SnowWhite) including 275 in spring, 266 in summer, 262 in autumn and 271 in winter and subjected to analysis by low background high-purity germanium gamma-ray spectrometery (ORTEC) to determine the activity concentrations of 7Be and 210Pb. Results:The activity concentrations of 7Be in atmospheric aerosol were from 0.56 to 14.84 mBq/m 3, with an avearage of 6.84 mBq/m 3, and from 0.01 to 9.37 mBq/m 3 for 210Pb, with an avearage 3.19 mBq/m 3. The differences in activity concentrations of 7Be and 210Pb in atmospheric aerosol among differernt seasons were statistically significant ( F=32.66, 93.93, P<0.05). Activity concentration of 7Be was highest in spring, followed by autumn, and lowest in summer and winter. Activity concentration of 210Pb ranged from winter, autumn, spring to summer in descending order. Conclusions:The activity concentrations of 7Be and 210Pb in atmospheric aerosol in Beijing from 2017 to 2020 fluctated within the range of normal level.