Objective To explore the set-up errors of position fixation with simple perforated foam pad in colorectal cancer radiotherapy and their causes as well as the improvement measures.Methods Sixty cases of color-ectal cancer patients undergoing radiotherapy were collected.Prone position was adopted with the position fixed by perforated foam pad and membrane.CBCT imaging was taken weekly before treatment,setup errors were corrected if necessary.Errors throughout the course of treatment for each patient were recorded and compared between patients, followed by analyzing the reasons of errors.Results Before calibration,the maximum errors on the direction of left and right (X-axis),front and back (Z),upside and downside (Y)in these 60 patients were 0.5cm,0.9cm and 0.7cm respectively with the average errors of (0.22 ±0.03)cm,(0.38 ±0.03)cm and (0.27 ±0.04)cm respec-tively.Conclusion The method of applying perforated foam pad and thermoplastic mask in colorectal cancer radio-therapy is currently the most commonly used in the clinical position fixation techniques,by which the small intestine, bladder and other pelvic tissues can be well protected.Due to poor comfort prone position,it is necessary to further improve perforated foam pad through improving the quality of the foam pad,thus improving patients comfort and posi-tioning repeatability and reducing position fixation errors.

Objective To compare the dosimetric differences between free-hand method and virtually optimized method for implanting needles in intracavitary and interstitial combined brachytherapy (IC/IS BT) of cervical cancer,and to explore the improvement space of the existing interstitial brahcytherapy plan.Methods High-dose-rate cervical cancer IC/IS BT plans (short for Treatment-Plan) of 18 cases were retrospectively analyzed.For each treatment plan,Nucletron Oncentra 3D brachytherapy planning system was utilized to redesign the virtually optimized insertion method IC/IS BT plan (short for Optimized-Plan).Dose volume histogram was adopted to evaluate the dose distribution in high-risk clinical target areas and exposure dose to organ at risk (OAR).The plan execution efficiency between two plans was also assessed.Results Comparing these two plans,the differences in conformity and uniformity of dose distribution of the target area were statistically significant (P=0.000,0.008).The differences of D0.01 cm3,D1 cm3,D2 cm3 and D5 cm3 in bladder,rectum,sigmoid and small bowel were all statistically significant (all P＜0.05).Optimized-Plan could reduce the D2 cm3 of bladder,rectum,sigmoid and small bowel by 60.41,36.43,27.53 and 12.43 cGy,respectively.The execution time for the Treatment-Plan and Optimized-Plan were (857.92±243.39) s and (804.53±239.13) s with statistical significance (P＜0.001).Conclusions Compared with the free-hand method,virtually optimized method yields more conformable coverage of the target area and more uniform dose distribution.At the same time,the doses of each OAR are reduced to different degrees and the execution time of the plan is also shortened.

Objective: To analyze factors affecting the delay in the case finding, treatment and diagnosis of tuberculosis among students during 2014-2020，and to provide a reference for the prevention and control measures of tuberculosis among students in Guiyang City. Methods: The medical cases of students with tuberculosis from 2014 to 2020 recorded by "China Disease Prevention and Control Information System" were collected and trend of delays in the detection, treatment, and diagnosis of students with tuberculosis were analyzed, and χ 2 test and multivariate Logistic regression were used to analyze influencing factors. Results: From 2014 to 2020, the rate of delay in the case finding, treatment, and diagnosis of tuberculosis among students in Guiyang showed a relatively stable trend. From 2014 to 2020, Guiyang City reported a total of 1 323 valid cases, the median number of case finding was 16 days,and 48.75% of student TB patients were delayed; the median number of treatment was 11 days, the delay rate of treatment was 43.46%; the median number of diagnosis was 0 day, the diagnosis delay rate was 11.87%. The results of multivariate Logistic regression analysis showed that the floating population was a risk factor for delay in case finding ( OR =1.45), the classification of the source of patients as "other" ( OR =0.19), the level of the first diagnosed unit was county ( OR =0.44), and the type of the first diagnosed unit was general hospital ( OR =0.58) were the protective factors for the delayed case finding of tuberculosis in students( P <0.05). Female ( OR =1.32) and floating population ( OR =1.38) were risk factors for delayed treatment. Floating population ( OR =1.51), rural areas ( OR =4.30), urban fringe ( OR =2.76),non severe patients ( OR =5.99) were risk factors for delayed diagnosis,females ( OR =0.65), ethnic minorities ( OR =0.38), college degree ( OR =0.53), and the first diagnosis unit wae a specialist hospital ( OR =0.22) were protective factors for delayed diagnosis of tuberculosis in students ( P <0.05). Conclusion The rates of tuberculosis case finding and treatment delay among students are common, which warrants targeted prevention and control measures to reduce the incidence of student delays and reduce the risk of tuberculosis cluster epidemics in schools.

Objective:To introduce the workflow of individualized 3D-printed intracavitary/interstitial vaginal template design. Dosimetric parameters and operation safety were investigated to evaluate the performance of 3D-printed template and freehand implantation.Methods:Forty patients previously treated with intracavitary/interstitial Ir-192 HDR brachytherapy were enrolled in this study. All patients were randomly divided into the treatment ( n=20) and control groups ( n=20). In the treatment group, twenty patients were treated with individualized 3D-printed template. CT-based preplan was carried out to determine the needle implantation cannels. Template with customized shape and implantation cannels was then produced by a 3D printer. Finally, the template was inserted under CT guidance. In the control group, twenty patients received freehand implantation. Needle insertion was decided empirically without the preplan process. Results:The difference of D 90 for high risk CTV was found to be minor, while the D 2cm 3 in the rectum, bladder and sigmoid was significantly improved in the treatment group. Meanwhile, the high dose region and conformal index were also improved in the treatment group. A total of 273 needles were inserted and one (0.3%) not-used needle was found. No normal tissues were penetrated during needle insertion in the treatment group. In the control group, a total of 203 needles were inserted and 4(2.0%) not-used needles were observed, and normal tissue penetration occurred in 3(1.5%) needle insertion. Conclusions:The individualized 3D-printed template implantation approach has advantages in terms of dosimetry and safety compared with freehand implantation. The actual treatment can achieve the dosimetric design requirements of the preplan.

Objective:To explore a three-dimensional dose distribution prediction method for the left breast cancer radiotherapy planning based on full convolution network (FCN), and to evaluate the accuracy of the prediction model.Methods:FCN was utilized to achieve three-dimensional dose distribution prediction. First, a volumetric modulated arc therapy (VMAT) plan dataset with 60 cases of left breast cancer was built. Ten cases were randomly chosen from the dataset as the test set, and the remaining 50 cases were used as the training set. Then, a U-Net model was built with the organ structure matrix as inputs and dose distribution matrix as outputs. Finally, the model was adopted to predict the dose distribution of the cases in the test set, and the predicted 3D doses were compared with actual planned results.Results:The mean absolute differences of PTV, ipsilateral lung, heart, whole lung and spinal cord for 10 cases were (119.95±9.04) cGy, (214.02±9.04) cGy, (116.23±30.96) cGy, (127.67±69.19) cGy, and (37.28±18.66) cGy, respectively. The Dice similarity coefficient (DSC) of the prediction dose and the planned dose in the 80% and 100% prescription dose range were 0.92±0.01 and 0.92±0.01. The γ rate of 3 mm/3% in the area of 80% and 10% prescription dose range were 0.85±0.03 and 0.84±0.02. Conclusion:FCN can be used to predict the three-dimensional dose distribution of left breast cancer patients undergoing VMAT.

【Objective】 To analyze the positive rate of antibodies against human leukocyte antigen(HLA)and MHC class I chain-related gene A(MICA) in the convalescent plasma from individuals recovered from COVID-19. 【Methods】 HLA-Ⅰ, -Ⅱ and MICA antibodies were screened simultaneously by Luminex platform. The specificity of HLA-Ⅰ and -Ⅱ antibodies was identified by single antigen reagents.The positive rate of antibody in different groups were compared by Chi-square test. 【Results】 A total of 88 cases of convalescent plasma were collected, among which the positive rates of HLA-Ⅰ, -Ⅱ and MICA antibodies were 18.19%, 19.32% and 10.23%, respectively, and 64 individuals (72.73%) were negative for HLA-Ⅰ and -Ⅱ antibodies. 95 blood donors were randomly selected as the control group, and the positive rate of HLA-Ⅰ, -Ⅱ and MICA antibodies were 8.42%, 13.68% and 10.53%, respectively, and 76 individuals(80.00%) were negative for HLA-Ⅰ and -Ⅱ antibodies. There were no significant difference in the positive rates of HLA-Ⅰ, -Ⅱ and MICA antibodies between convalescent individuals and control group. The specificity of HLA antibody to epitopes was different in each convalescent individual with positive HLA antibodies, and most antibodies were targeted to the epitopes of multiple HLA alleles. 【Conclusion】 A certain proportion of HLA antibody was found in the convalescent plasma of individuals recovered from COVID-19. Therefore, HLA antibody screening is helpful to improve the safety of transfusion.