Objective:To study the influence of intensive magnet fields on radiation dose measurement, and to demonstrate the feasibility of measuring magnet field correction factor by a combination of medical linac with variable magnet fields in view of needing for accurate measurement of the doses from reference beam arising in MR image-guided radiotherapy.Methods:A photon radiation field and a variable field with 6 MV nominal high voltage were produced by using conventional medical electron linear accelerator equipped with a pair of electromagnets with magnetic field strength up to 1.5 T. Both PTW30013 and PTW31010 ionization chambers were used to test the responses of ionization chambers under different magnetic field strengths at four orientations in which the angles between ionization chamber axis and magnetic field direction were 0°, 180°, 90° and 270°, respectively. The magnetic factors, kB, M was calculated and compared with the reported values in literature. Results:The response of ionization chamber was proportional to the magnetic field strength before it reached to a peak around 1 T, and then fell down as the magnetic field continued to rise. When the magnetic field was 0.35 T, the magnetic factors of PTW31010 were 0.988 2±0.000 3 and 0.997 4±0.000 4 corresponding to 90° and 0° directions, the discrepancy between 0° scenario and literature was 0.05% ± 0.04%. When the magnetic field reached 1.5 T, the magnetic factor of PTW30013 was 0.958 9±0.000 5 at the situation of 90°, which was 0.60% ± 0.05% different from the literature value.Conclusions:Conventional 6 MV medical accelerator equipped with electromagnet can be used to measure the magnetic field factor of reference dosimetry for MRIgRT.

Several new glass vessels, thermistor probes, and water phantoms have been designed and built at the National Institute of Metrology (China) to upgrade and develop the existing water calorimeter. The increased plane-parallel vessels have shorter thermal stability times and shallower positioning depths (∼1.3 cm) than the previous cylindrical vessels, which makes them suitable for electron beams. The sensitivity of the new probes is 10% greater than the previous ones. In this study, detailed experimental and theoretical investigations of various factors affecting the new water calorimeter are performed. The system uncertainty of the water calorimeter is reduced and the robustness of the determination of the absorbed-dose-to-water D w is improved using a variety of geometric detector vessels and two kinds of high-purity water systems saturated with high-purity gases. This new calorimeter is employed as a primary standard for determining the D w , has achieved a combined standard uncertainty of 0.24% for a 60 Co beam, 0.27% for 6 MV and 10 MV photon beams and 0.30% for a 25 MV photon beam. The beam quality conversion factors k Q of ten cylindrical and three plane-parallel ionization chambers are measured using the new calorimeter to improve the reference dosimetry accuracy of high-energy clinical photon beams.

文章首先对BIM技术进行了概述,其次说明了BIM技术在深基坑工程中的应用现状,最后探究了BIM技术在深基坑工程各阶段中的具体应用,包括设计阶段、施工阶段、监测阶段.

随着煤炭采深日益增加,围岩变形破坏的问题在深埋软岩巷道中越来越突出.以宿州朱仙庄煤矿Ⅱ836工作面风巷为主要研究对象,通过运用理论分析、计算等手段,对巷道进行了支护方案设计,并应用"十字布点法"对巷道围岩变化进行了观测.观测结果表明,巷道变形量较小,可以满足巷道安全使用要求.