Objective To study the step aceuracy of 252Cf neutron afterloading radiotherapy machine and the dose deviation caused by step deviation.Methods EBT3 film was used to measure the steps of the 252Cf neutron source,and then the center of each 252Cf neutron source was identified by measuring the optical density value by using the ImageJ software.Double ion chambersmethod was used to measure the dose deviation dlue to the 252 Cf neutron source position shift.Results 252 Cf neutron source step accuracy may amount to 0.01 mm using EBT3 film measurement,when 252Cf neutron source position deviation is less than 3 mm,the dose deviation is less than 2.5％.Conclusions The study on the step accuracy and position deviation of the 252Cf neutron source can provide a reference for the quality control standard of the 252Cf neutron afterloading radiotherapy machine.

OBJECTIVE:To optimize the extraction technology of Compound Rhodiolae crenulatae granule. METHODS:The pharmacodynamic index of learning and memory ability was used to screen the water extraction,water extraction and alcohol pre-cipitation and alcohol extraction methods for Compound R. crenulatae granule in mice by Y-type water maze test. Using the compre-hensive scores of salidroside,ferulic acid extraction amount and extraction yield as indexes,orthogonal test was used to optimize the ethanol volume fraction,extraction time,solvent amount and extraction times,and verification test was conducted. RESULTS:Products by alcohol extraction can significantly improve learning and memory ability in the 3 methods;the optimal extraction tech-nology was confirmed to 8-fold 70% ethanol reflux extracting for 3 times,1.0 h each time. In verification test,average extraction amount of salidroside and ferulic acid were 4.884 mg/g and 1.669 mg/g,and average extraction yield was 33.52%(all RSD<2%, n=3). CONCLUSIONS:The optimized extraction technology is stable,reliable,simple and feasible,which can be used for indus-trial extraction of Compound R. crenulatae granule.

Objective To establish testing and evaluation methods for radiation shielding performance of a self-shielded radiotherapy system by measuring the radiation levels around the self-shielded head and neck radiotherapy system. Methods A total of 14 monitoring points were selected outside the restricted zone of the system. Under radiation conditions from five different fixed directions, an ion chamber survey meter was used to measure and identify the maximum ambient dose equivalent rate at the 14 points. The time-averaged dose rate was then calculated based on the workload. In accordance with relevant radiation protection standards, an instantaneous dose rate of 10 μSv/h and a time-averaged dose rate of 2.0 μSv/h were proposed as the criteria for shielding protection evaluation. Results Based on the ambient dose equivalent rates at the 14 monitoring points outside the restricted zone, the maximum instantaneous dose rate outside the restricted zone was 7.4 μSv/h. With a workload of 15 patients per day, the maximum time-averaged dose rate was 1.0 μSv/h, which can be used as the criteria for shielding protection evaluation. Conclusion By considering both instantaneous dose rate and time-averaged dose rate, a comprehensive safety assessment of the radiation shielding performance of a self-shielded radiotherapy system can be conducted.