Holeman G R, Price K W, Friedman L F, Nath R
Med Phys. 1977 Nov-Dec;4(6):508-15. doi: 10.1118/1.594339.
High-energy x-ray radiotherapy machines in the supermegavoltage region generate complex neutron energy spectra which make an exact evaluation of neutron shielding difficult. Fast neutrons resulting from photonuclear reactions in the x-ray target and collimators undergo successive collisions in the surrounding materials and are moderated by varying amounts. In order to examine the neutron radiation exposures quantitatively, the neutron energy spectra have been measured inside and outside the treatment room of a Sagittaire medical linear accelerator (25-MV x rays) located at Yale-New Haven Hospital. The measurements were made using a Bonner spectrometer consisting of 2-, 3-, 5-, 8-, 10- and 12-in.-diameter polyethylene spheres with 6Li and 7Li thermoluminescent dosimeter (TLD) chips at the centers, in addition to bare and cadmium-covered chips. The individual TLD chips were calibrated for neutron and photon response. The spectrometer was calibrated using a known PuBe spectrum Spectrometer measurements were made at Yale Electron Accelerator Laboratory and results compared with a neutron time-of-flight spectrometer and an activation technique. The agreement between the results from these independent methods is found to be good, except for the measurements in the direct photon beam. Quality factors have been inferred for the neutron fields inside and outside the treatment room. Values of the inferred quality factors fall primarily between 4 and 8, depending on location.
超高能区域的高能X射线放射治疗机能产生复杂的中子能谱，这使得对中子屏蔽进行精确评估变得困难。X射线靶和准直器中的光核反应产生的快中子在周围材料中经历连续碰撞，并以不同程度被慢化。为了定量检查中子辐射暴露情况，在位于耶鲁-纽黑文医院的一台Sagittaire医用直线加速器（25兆伏X射线）治疗室的内部和外部测量了中子能谱。测量使用了一个邦纳谱仪，它由直径为2英寸、3英寸、5英寸、8英寸、10英寸和12英寸的聚乙烯球组成，球心放置有6Li和7Li热释光剂量计（TLD）芯片，此外还有裸芯片和镉覆盖芯片。各个TLD芯片针对中子和光子响应进行了校准。该谱仪使用已知的钚铍谱进行了校准。谱仪测量在耶鲁电子加速器实验室进行，并将结果与中子飞行时间谱仪和活化技术进行了比较。发现除了在直接光子束中的测量结果外，这些独立方法的结果之间的一致性良好。已经推断出治疗室内部和外部中子场的品质因数。推断出的品质因数的值主要在4到8之间，具体取决于位置。
