移动式加速器术中放射治疗辐射场剂量水平的测量与分析

Measurement and analysis on the radiation level of Intra-operative radiotherapy(IORT) with a mobile accelarator

目的掌握移动式加速器(简称加速器)术中放射治疗时在手术室及其外围产生的辐射水平,制订手术室可行的屏蔽设计方案,加强术中放射治疗的防护管理。方法以某医院设置的1台Mobetron移动式加速器和术中放射治疗场所为研究对象,采用12MeV电子束、输出量率1000cGy/min进行模拟术中放射治疗,分别使用LiF(Mg,Cu,P)热释光剂量计(TLD)和6150-AD型环境剂量率仪对术中放射治疗手术室内及其外围的辐射水平进行测量。结果 (1)术中放射治疗手术室内的辐射场剂量水平及其分布:Z=75cm平面(治疗床平面)内,加速器前方100cm处的剂量率为40.8～62.8mGy/h,后方100cm处的剂量率为0.13～11.2mGy/h;加速器前方和侧向300cm处的剂量率为2.05～6.35mGy/h。(2)术中放射治疗辐射安全设置状况及手术室外围的辐射水平:术中放射治疗手术室及其准备间设为控制区,防护门均与出束联锁;照射时东墙外走廊(中间隔有准备间)最高剂量率为9.0μGy/h,北墙外控制室内最高剂量率为19.5μGy/h,西墙外清洁走廊和南墙外、楼下场所最高剂量率分别为24.2、14.5和23.0μGy/h。结论加速器在手术室内产生的辐射主要为轫致辐射的杂散辐射,但应相对固定术中放射治疗场所并结合实测辐射值制订并优化场所的屏蔽设计方案。

Objective To enhance the protective management and to design a feasible shielding project by measuring the real radiation level of Intra-operative radiotherapy （IORT） with a mobile accelerator （accelerator） in/outside the operating room. Methods A Mobetron mobile accelerator and the operating room were selected as the research object. Under the condition of simulating IORT with 1000cGy/min of 12MeV electron beam, the radiation level both from the IORT operating room and from its peripheral place were obtained by the test tools including LiF（ Mg, Cu,P）thermoluminescent dosimeters（TLDs） , an environmental dose rate meter typed 6150-AD. Results （1）The radiation level and dose distribution in the IORT operating room. In the Z =75 plane（couch plane）, an exposure value of approximately 40. 8 -62. 8mGy/h at 100cm in the front of the unit and a value of approximately 0.13 - 11.2mGy/h at 100cm at the back of the accelerator were measured, while a value of approximately 2. 05 - 6.35mGy/h at 300cm in the front of the device and at the lateral of the unit. （2）The radiation safety setting of the IORT operating room and the radiation level outside the room. The IORT operating room and its preparing rooms were regarded as controlled area and all doors of the site were interlocked with beam on. Under the circumstance of the above radiation state set, there were maximum of 9.0μGy/h in the aisle （which is separated by the preparing rooms） outside east wall and 19.5 μGy/h in the controlling room outside north wall of the operating room. At the same time, 24.2, 14.5 and 23.0μGy/h were shown as the maximum value from clean hall outside west wall, the place outside south wall and under the floor correspondingly. Conclusion The radiation resulted from IORT accelerator operation was belong to mixed scatter radiation of hremsstrahlung in the operating room. It is desirable that an IORT operating room should be located at an appropriate immovable place and the shielding design plan should be determined and optimized on the basis of practical radiation level.