Yudelev M, Maughan R L, Jordan L E, Saxena R
Gershenson Radiation Oncology Center, Wayne State University, Detroit, MI 48201, USA.
Health Phys. 1997 Mar;72(3):361-7. doi: 10.1097/00004032-199703000-00003.
The sources of the induced activity from the d(48.5)+Be fast neutron therapy beam of the Harper Hospital superconducting cyclotron have been investigated. The distribution of activity in the treatment room was measured, and the levels of dose equivalent to the staff were established. Activation spectra were measured with a high purity RE-Ge detector. Peaks corresponding to 28Al, 56Mn, 24Na, 64Cu, 66Cu, and 187W were present in the spectra. The dose equivalents due to the induced activation were measured by means of an ionization chamber type survey meter at six locations in the room. Irradiations of 120 monitor units were given at 15-min intervals, thus simulating the clinical situation. The measurements were made between the irradiations. The highest levels were registered around the treatment head. Two patterns are clearly distinguishable in these measurements. A fast decaying component with approximately 2 min half-life can be ascribed predominantly to 28Al and a slow growing component reaching saturation after about 4-5 treatments is associated with the presence of 56Mn. For uniform treatment load the activation build-up in each location was similar every day of the week with minimal values measured after the week end shut down. Personnel monitoring is achieved with dosimeters capable of detecting an extended range of neutron energies as well as beta rays and photons. Correlation between the number of fields treated and the doses to the radiation therapy technologists was shown. The mean dose equivalent received by the therapists is 7.1 +/- 0.2 microSv per treatment field. Means of reducing personnel dose equivalent levels are proposed.
已对哈珀医院超导回旋加速器的d(48.5)+Be快中子治疗束产生的感生放射性来源进行了研究。测量了治疗室内的放射性分布，并确定了工作人员的剂量当量水平。用高纯锗探测器测量了活化谱。谱中出现了对应于28Al、56Mn、24Na、64Cu、66Cu和187W的峰。通过电离室型巡测仪在室内六个位置测量了感生活化产生的剂量当量。以15分钟的间隔进行120个监测单位的照射，从而模拟临床情况。在照射期间进行测量。最高水平记录在治疗头周围。在这些测量中可清楚区分出两种模式。半衰期约为2分钟的快速衰减成分主要可归因于28Al，而在约4-5次治疗后达到饱和的缓慢增长成分与56Mn的存在有关。对于均匀的治疗负荷，每周的每一天每个位置的活化积累情况相似，在周末停机后测量到最小值。通过能够检测广泛中子能量以及β射线和光子的剂量计来实现人员监测。显示了治疗野数量与放射治疗技术人员所受剂量之间的相关性。治疗师每次治疗野平均接受的剂量当量为7.1±0.2微希沃特。提出了降低人员剂量当量水平的方法。
