Objective To conduct Monte Carlo simulations on the microselectro-HDR¹⁹²Ir radiation source, investigate dose distributions under various conditions, and provide assistance in optimizing radiotherapy plans. Methods A microselectro-HDR¹⁹²Ir radiation source model was established based on the MCNP5 software. Theoretical calculation formulas were used to validate the simulation results. The dose distributions under different activities and positions were obtained through simulations using the MCNP5 transport program. By fitting the simulation data, the relationship between the safe distance for at-risk organs and treatment time was analyzed. Results As the distance from the origin increased in the X-direction, the distance required for the absorbed dose rate to decrease to half its original value increased, and the isodose lines became sparser. The shapes of the dose distribution diagrams under different activities were consistent, presenting concentric polygons and concentric circles at different distances. Under the condition of the same lethal dose, the difference in the safe distance between two organs increased with time; under different lethal dose conditions, the differences were not significant whether between similar organs or between different organs. Conclusion The Monte Carlo method can accurately describe the radiation field generated by the microselectro-HDR¹⁹²Ir radioactive source during high-dose-rate brachytherapy. Quantitative analysis of the radiation field will help optimize the radiotherapy plan.

Objective To conduct Monte Carlo simulations on the microselectro-HDR¹⁹²Ir radiation source, investigate dose distributions under various conditions, and provide assistance in optimizing radiotherapy plans. Methods A microselectro-HDR¹⁹²Ir radiation source model was established based on the MCNP5 software. Theoretical calculation formulas were used to validate the simulation results. The dose distributions under different activities and positions were obtained through simulations using the MCNP5 transport program. By fitting the simulation data, the relationship between the safe distance for at-risk organs and treatment time was analyzed. Results As the distance from the origin increased in the X-direction, the distance required for the absorbed dose rate to decrease to half its original value increased, and the isodose lines became sparser. The shapes of the dose distribution diagrams under different activities were consistent, presenting concentric polygons and concentric circles at different distances. Under the condition of the same lethal dose, the difference in the safe distance between two organs increased with time; under different lethal dose conditions, the differences were not significant whether between similar organs or between different organs. Conclusion The Monte Carlo method can accurately describe the radiation field generated by the microselectro-HDR¹⁹²Ir radioactive source during high-dose-rate brachytherapy. Quantitative analysis of the radiation field will help optimize the radiotherapy plan.

Objective To conduct Monte Carlo simulations on the microselectro-HDR¹⁹²Ir radiation source, investigate dose distributions under various conditions, and provide assistance in optimizing radiotherapy plans. Methods A microselectro-HDR¹⁹²Ir radiation source model was established based on the MCNP5 software. Theoretical calculation formulas were used to validate the simulation results. The dose distributions under different activities and positions were obtained through simulations using the MCNP5 transport program. By fitting the simulation data, the relationship between the safe distance for at-risk organs and treatment time was analyzed. Results As the distance from the origin increased in the X-direction, the distance required for the absorbed dose rate to decrease to half its original value increased, and the isodose lines became sparser. The shapes of the dose distribution diagrams under different activities were consistent, presenting concentric polygons and concentric circles at different distances. Under the condition of the same lethal dose, the difference in the safe distance between two organs increased with time; under different lethal dose conditions, the differences were not significant whether between similar organs or between different organs. Conclusion The Monte Carlo method can accurately describe the radiation field generated by the microselectro-HDR¹⁹²Ir radioactive source during high-dose-rate brachytherapy. Quantitative analysis of the radiation field will help optimize the radiotherapy plan.

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.

Objective:To analyze the levels of individual doses to radiation workers receiving medical radiation exposure in hospitals in Jiangxi province, so as to provide reference for radiation protection.Methods:The radiation workers of different types in medical institutions in Jiangxi were investigated from 2014 to 2018, involving diagnostic radiology, radiotherapy, nuclear medicine and interventional radiology. Statistical analyses were made of the individual doses to medical radiation workers in the province.Results:The total number of monitored workers were 23 833 with average annual individual effective dose of 0.316 mSv. NR1 and NR5, the ratios of the number of workers receiving annual individual doses exceeding 1 and 5 mSv to the total monitored workers were 4.32% and 0.10%, respectively. During the five-year period, the average annual individual effective dose showed a upward and then downward trend, with peak appearing in 2017. A total of 17 909 diagnostic radiologists were monitored, accounting for 75.14% of the total number of monitored workers. The average annual individual effective dose received by workers was 0.329 mSv, the highest, in interventional radiology, followed by diagnostic radiology 0.318 mSv, nuclear medicine 0.283 mSv, and radiotherapy 0.269 mSv, respectively. There were statistically significant differences among radiation workers of different types ( χ2=489.39, P<0.001). Conclusions:The average annual individual effective dose to the radiation workers in medical institutions in Jiangxi province meets the relevant national standards, but with an upward trend in nuclear medicine. The higher levels of individual doses to radiation workers are seen in primary and secondary hospitals. It should be strengthen the oversight of radiation workers in nuclear medicine and in primary and secondary hospitals.

Objective To investigate the reasons why the routine monitoring of personal dose of occupational external exposure of some radiological workers in our province reached the investigation level in 2018, so as to provide technical support for the correct decision making of administrative departments. Methods The registration forms for monitoring and verifying the personal dose of occupational external exposure were issued to radiation workers whose periodic dose reached or exceeded 1.25 mSv/ cycle. Results A total of 102 person-times were sent out in 53 verification forms, and 95 person-times were collected in 47 copies. The recovery rate was 88.68%, and 7 person-times did not feedback the verification forms. There were 15 cases of actual exposure, accounting for 15.79%, including 5 cases of radiological diagnostic staff, who did not close the protective door when operating exposure. Among them, the other 80 cases, accouting for 84.21% didn't receive actual exposure. Conclusion The vast majority of radiological workers who reached the survey level didn't receive actual exposure. 5 person-time radiological diagnostic staff, during the work did not close the protective door, subjected to abnormal radiation. Interventional medicine, nuclear medicine and industrial mobile flaw detection workers are at higher risk of abnormal exposures during their work. The suspicious results of the questionnaires without feedback were all less than the annual dose limit and the requirements of audit management. We will strengthen supervision of radiation health protection, raise the awareness of radiation protection among radiation workers, and improve radiation protection management and protection conditions for radiation workers in interventional medicine, nuclear medicine and industrial mobile flaw detection furtherly.

Objective To study the frequency of diagnostic medical radiological examinations and the distribution of examinees in Jiangxi province by sampling investigation,including normal X-ray diagnosis,computed tomography (CT),interventional radiology.Methods Hospitals of different levels in Jiangxi province were chosen by the typical sampling method.Questionnaire was used in this study.Results There were more male examinees than female in diagnostic medical radiological examinations.For the distribution of age,the "0-" group accounted for the lowest and the "40-" group the highest proportion.The annual frequency in 2016 in Jiangxi was 543.07 examinations per 1 000 population for normal X-ray diagnosis,244.79 examinations per 1 000 population for CT scanning,6.28 examinations per 1 000 population for interventional radiology.Conclusions The frequency of diagnostic medical radiological examinations in Jiangxi has been increased rapidly which made a huge challenge for radiological protection.Therefore,the supervision and management of diagnostic medical radiological examinations should be enhanced and medical resources should be rationally allocated.

Objective: To study the frequency of clinical nuclear medicine procedures and the distribution of examinees in Jiangxi povince, and to estimate the annual frequency of clinical nuclear medicine procedures in Jiangxi in 2017. Methods: A survey was made with questionnaires on all medical institutions carrying out clinical nuclear medicine practices in the province. Results: Except for positron emission tomography (PET) examinations, the frequency of nuclear medicine procedures for females was much higher than that for males. The total frequency of nuclear medicine procedures was 0.67 examinations per 1 000 population in 2017, and the frequencies for diagnosis and treatment were 0.58 and 0.09 examinations per 1 000 population, respectively. Conclusions The frequency of clinical nuclear medicine procedures in Jiangxi increased rapidly after the "Ninth Five-Year Plan" period. It is necessary to further standardize the diagnosis and treatment of nuclear medicine procedures, to enhance the awareness of radiation protection of nuclear medicine staff and to promote the healthy and orderly development of nuclear medicine.

Objective: To Effects of n-hexane on learning and memory and the expressions of nerve growth factor (NGF) mRNA and nerve growth factor receptor (NGFR) mRNA of brain tissue in mice exposed to N-hexane. Methods: 40 Kunming mice were randomly divided into low-dose group, meddle-dose group, high-dose dose group and control group, with 10 mice in each group. All the groups were orally exposed to n-hexane in different doses: low-dose group with 43.5 mg/kg, middle-dose group with 86.5 mg/kg and high-dose group with 173.0 mg/kg, 1 time per day for 20 d. After the poisoning, the Y-arm test and the expressions of NGF mRNA and NGFR mRNA and the concentrations of NGF and NGFR in the brain tissues of each group were measured. Results: In the first Y-arm test, there existed a significant difference in correct reaction rate generally in all groups (P<0.05), and correct reaction rate in the middle-dose group and the high-dose group were low significantly compared with that in the control group(P<0.05). In the second Y-arm test, there existed a significant differences in total electric shock time and correct reaction rate generally in all groups (P<0.01), and the total electric shock time prolonged significantly and the correct response rate decreased significantly in 3 dose groups compared with those of the control group(P<0.05). The expression levels of NGF mRNA in brain tissues of low, meddle and high dose-groups were 0.81±0.66, 0.67±0.37 and 0.69±0.26, and the expression levels of NGFR mRNA were 1.22±0.42, 1.98±0.84 and 2.01±2.01, respectively. Compared with the control group, the expressions of NGF mRNA in the 3 dose groups decreased significantly (P<0.05), and the expression of NGFR mRNA in middle-and high-dose groups increased significantly (P<0.05). The concentrations of NGF in brain tissues of low,meddle and high dose-groups were 39.97±7.24 ng/L, 39.26±7.88 ng/L,31.70±8.21 ng/L,and the concentrations of NGFR were 17.37±6.82 ng/L,21.37±7.16 ng/L, 22.46±7.70 ng/L, respectively. Compared with the control group, the concentrations of NGF in high-dose groups decreased significantly(P<0.05), and the concentrations of NGFR in middle-and high-dose groups increased significantly (P<0.05). Conclusion N-hexane exposure can result in decrease of learning and memory in mice, which may be related to abnormal expression of NGF mRNA and NGFR mRNA in brain tissue.

OBJECTIVETo explore the clinical efficacy of GEMOX regimen on patients with refractory non-hodgkin's lymphoma.

METHODSEighty-two cases of non-Hodgkin's lymphoma were divided into 2 groups: gemcitabine+oxaliplation(Gem+Oxa) group (42 cases) and vinorelbine+oxaliplatin(Vin+Oxa) group (40 cases) according to chemotherapy regimens. The clinical efficacy, side effects, progression-free survival situation in 2 groups were compared.

RESULTSThere was no significant difference on the clinical effects of 2 groups (P>0.05); The therapeutic efficacy for B cell lymphoma was higher than that for T cell lymphoma(P<0.05); The therapeutic effects for I-II stages was lower than that for III-IV stages(P<0.05); The incidences of platelet decline, nausea and vomit, peripheral nerve symptoms in Gem+Oxa group were lower than those in Vin+Oxa group(P<0.05); There was no significant difference in the median progression free survival(P>0.05).

CONCLUSIONThe efficacy of GEMOX regimen for refractory non-Hodgkin's lymphoma has been confirmed to be good, it has distinct clinical curative effect, it can prolong the progression-free survival time in patients with B cell lymphoma, specially for III-IV stages. It can be used as the preferred method for the treatment of patients with refractory NHL.