The paper mentioned that prevention of disease was a n independent subject in preventive medicine and expounded the definition, study contents, study methods, study targets and study scopes of the subject. The rel ationships and differences between prevention of disease and other subjects were discussed. The paper introduced advancements of study of this subject.

There is a tendency that the mortality of cerebrovascular disease increases with age.The data from several communities was mathematically analogized, and the mathematical model of age distribution of cerebrovascular disease mortality was establishedby using the exponential curve, Y = aebx .The model gives an account of the law ofage distribution of cerebrovascular disease mortality.The increment rate and"the increment multiple constant"of the increment rate of cerebrovascular disease mortality withage are calculated by using its differential equation, dy/dx =abebx. The two numeralsmay be used as indexes for comparison with risk degree and distribution law of cerebrovascular disease among several communities.In addition, the model may be used to predict cerebrovascular disease mortality and to evaluate the effect of preventive and curative measures for cerebrovascular disease.

Objective　To study killing effect of plasmas ozo ne water on microorganisms by plasmas ozone disinfection solution through plasma s ozone resulting from discharge along surface disinfection solution produced by machine and its effect factors. Methods　Quantitative solut ion test was used to study killing action of plasmas ozone disinfection water to E. coli and staphyrococcus aureus, and to study its eff ect factors. Results　Plasmas ozone water could kill 99.9% E. coli and staphyrococcus aureus after 15 min. The kill ing effect was affected by organism. With the increasing of organism concertrat ion, the killing efficacy increased. Conclusions　Plasmas ozone can effectively kill microorgnisms in water and the efficacy was affected by org anism.

The killing effects of five chemical disinfectants on hepatitis A virus (HAV) were determined by ELISA The results showed that 2% glutaraldehyde completely killed HAV within 10 min and 025% peracetic acid killed 74.5% HAV within 5 min and 40% iodophors killed 60.3% HAV within 5 min. It is suggested that glutaraldehyde, peracetic acid and iodophors are more effective agents to kill HAV.

Objective　To study efficacy of 2,4-dibromo-5, 5-d imethylhydantoin in killing vegetative forms of bacteria and spores of B. subtil is var.niger, and efficacy of 2,4-dibromo-5,5-dimethylhydantoin in dest roying antigenicity of HBsAg. Methods　Neutralizer test and efficacy of so lution of 2,4-dibromo-5,5-dimethylhydantoin in killing vegetative forms of ba cteria and spores. Neutralizer test and efficacy of solution of 2,4-dibromo-5, 5-dimethylhydantoin in destroying HBsAg antigenicity in suspension. Resul ts　The killing rate of Staphylococcus aureus and E. coli. was 100 % a fter exposure to its solution containing 4 mg*L-1 and 2 mg*L-1 av ailable bromo after 10 min and 20 min. The killing rate of spores of Bacil lus subtilis var. Niger also was 100% after exposure to its solution co ntainin g 2 000 mg*L-1 available bromo after 30 min. Its solution containing 1 0 00 mg*L-1 available bromo with could destroy HBsAg in su spension for 5 min. Conclusions　2,4-dibromo-5,5-dimethylhydantoi n can effe ctively kill vegetative forms of bacteria and spores of B. subtilis var.ni ger, and can completely destroy the antigenicity of HBsAg in the water.

A large-scale population survey has been made to clarify the degree of harm and feature of distribution of cerebrovascular disease (CVD) in China. The sample investigated was 5814851 from about a billion people in 29 provinces, municipal cities and autonomous regions except Taiwan in China. The incidence, prevalence and mortality rates have been standardized by the direct method using the world standard population. It has been found that the incidence rate of CVD in China was 109.95 per 100 000 people in 1986 and its 95%CI (confidence interval) was 107. 25 ~ 112. 65 per 100000. The age-standardized incidence rate was 115.87/100000. The point prevalence rate of CVD in China was 245.49 per 100000 people on December 31, 1986 and its 95%CI was 241.57-249.61 per 100000, with an age-standardized prevalence rate of 259.86 per 100000. The mortality rate of CVD was 76.78 per 100000 in 1986 and its 95%CI 74.52~79.04 per 100000, with an age-standardized mortality rate of 80.94 per 100000. It has also been found that there was a tendency for the rates to increase gradually from south to north and to decrease progressively from east to west. The models of linear regression have been established between latitude and rates as well as between longitude and rates, respectively. The incidence, prevalence and mortality rates of CVD differ significantly in various topographic areas. They were much higher in cities than in rural areas, and much higher in men than in women. The incidence, prevalence and mortality rates increased with the age, and their relationships were fitted with logistic curve, respectively.

Point prevalence rate of complete stroke on December 31, 1986 in China was investigated using a retrospecive section study for 5 814 851 people of 29 provinces and cities (excluding Taiwan province), and 14275 stroke cases were found. Point prevalence rate was 245.49 per 100000 people with 95% CI (confidence interval) 241.57-249.61 per 100000 people. The rate standardized by the constituent ratio of population between city and rural area of China in 1986 was 247.66 per 100000 people. The rate age-standardized by the population of China in 1982 accounted for 191.92 per 100000 and the rate agestandardized by the world standard population was 259.86 per 100000 people.It has also been found that there was a tendency for the prevalence rates to increase gradually from south to north and to decrease progressively from east to west. The linear regression models have been fitted between the point prevalence rates and latitude or longitude respectively. The results were Y= 12.3819?-1107.38 (tb = 4.65 df = 5 P = 0.0056) for longitudes and Y = 12.6279?-146.6266 (tb = 11.7517 df = 4 P = 0.0003) for latitudes. There was a difference statistically among various topographic areas. The prevalence rate was much higher in urban areas than rural areas and much higher in men than in women. The prevalence rate increased with age and their relationships have been fitted well with the logistic curve.

Objective: To investigate the effect of Utrecht applicator on dosimetrics of targets and OARs in brachytherapy for advanced cervical cancer. Methods: Data of patients with locally advanced cervical cancer who received brachytherapy with Utrecht Source Applicator from 2017 to 2018 in the Department of Radiotherapy, Cangzhou Hospital of Integrated Traditional Chinese and Western Medicine, Hebei province, were collected. The original plan was intracavitary /interstitial brachytherapy (IC/IS-BT). With the original contour and prescription dose unchanged, the implantation was removed and new intracavitary brachytherapy (IC) plan was designed. The dosimetric parameters of IC/IS plan and IC plan were compared and analyzed, and the effect of IS implantation on dose was evaluated. Results: The D₉₀ of HR-CTV was (88.68±1.84) Gy in IC/IS group and (85.54±0.54) Gy in IC group, with significant difference(t=6.200, P<0.05). In addition, conformity index of the IC/IS plan was significantly higher than that of the IC plan (IC/IS: 0.58±0.08, IC: 0.43±0.05; t=1.010, P<0.05). In terms of OAR, there was no significant difference in dosage between the two groups (P>0.05). Conclusions For the brachytherapy of locally advanced cervical cancer, the use of Utrecht Source Applicator can satisfy the prescription dose coverage. Adding IS insertion needle can improve the optimization space of the plan. Without exceeding the dose limit of OAR, the radiation dose to HR-CTV can be significantly increased, and the uniformity of dose distribution can be improved as well.

Objective To compare the difference of dose distribution between inverse planning simulated annealing (IPSA) and hybrid inverse treatment planning and optimization (HIPO) in 3D brachytherapy plan of cervical cancer,and to provide evidence for selection of reverse planning optimization method for cervical cancer brachytherapy.Methods From Dec 2016 to May 2017,totally 43 cases of patients with cervical cancer radical surgery were selected.Original IPSA brachytherapy treatment plan optimization was applied to all cases.Based on the information of original image,IPSA and HIPO plans were established according to the same initial conditions.Parameters of Dg0,D100,V100％,Homogeneity Index (HI),and conformal index (CI) of the bladder,rectum and sigmoid D2 cm3 data for High-Risk Clinical Target Volume (HR-CTV) were assessed.Results There was no statistically significant difference in D90,D100 and CI for HR-CTV between the two groups.But the V100％ of HR-CTV in HIPO group was significantly higher than that in IPSA group [(87.72 ±0.49)％ vs.(85.01 ± 0.55)％,t =2.54,P ＜0.05].Furthermore,HI in HIPO group was (0.51 ±0.08),which was higher than that in IPSA group (0.42 ± 0.06),and the difference was statistically significant (t =3.02,P ＜ 0.05).Compared with IPSA,bladder D2 cm3 and rectum D2 cm3 [(3.04 ± 0.37) Gy] for HIPO plan were lower [(3.42 ± 0.17) Gy vs.(3.57 ± 0.28) Gy,(3.04 ± 0.37) Gy vs.(3.57 ± 0.28) Gy],which had reached statistical significance (t =0.27,0.19,P ＜ 0.05).There was no statistical significance in the D2 cm3 dose of sigmoid.Conclusions In the treatment of cervical cancer,better target area HI and less irradiated dose of bladder and rectum can be obtained by HIPO optimization than IPSA optimization.

Objective:To customize the individualized 3D printed head film for patients with head tumors undergoing radiotherapy, and to evaluate the physical properties of the material and the precision of this technology compared with the thermoplastic head film.Methods:The 3D printed head film and thermoplastic head film were placed on the solid water surface, and the depth and surface dose were measured at 5 cm by ionization chamber and film, respectively. Thirty patients with head tumors receiving radiotherapy were randomly divided into the control and experimental groups. The patients were fixed with thermoplastic head film and 3D printed head film. The translational and rotational errors in the x, y and z direction were obtained by CBCT.Results:The radiation attenuation rate of two materials at the depth of 5 cm was less than 1%. The dose of thermoplastic head film in the surface position was increased by 27%, and increased by 18% in the 3D printed head film. In two groups, 116 sets of setup errors were collected. The average translational setup errors in the control and experimental groups were 1.29 mm and 1.16 mm, 1.42 mm and 1.24 mm, 1.38 mm and 1.16 mm, respectively, and the average rotational setup errors were 1.29°and 1.08°, 1.02°and 0.96°, 1.01°and 1.00°, respectively. The translational setup errors in the y and z direction and rotational setup errors in the x direction significantly differed between the control and experimental groups (all P<0.05), but no statistical significance was found in the other direction (all P>0.05). Conclusion:The 3D printed head film fixation meets the precise setup requirements of modern radiotherapy, which deserves further application in clinical trials.