Mishra Bibekananda, Selvam T Palani, Sharma P K Dash
Radiological Safety Division, Atomic Energy Regulatory Board, Niyamak Bhavan, Mumbai, Maharashtra, India.
Radiological Physics and Advisory Division, Health Safety and Environmental Group, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India.
J Med Phys. 2017 Jan-Mar;42(1):18-24. doi: 10.4103/jmp.JMP_99_16.
Detailed structural shielding of primary and secondary barriers for a 6 MV medical linear accelerator (LINAC) operated with flattening filter (FF) and flattening filter free (FFF) modes are calculated. The calculations have been carried out by two methods, one using the approach given in National Council on Radiation Protection (NCRP) Report No. 151 and the other based on the monitor units (MUs) delivered in clinical practice. Radiation survey of the installations was also carried out. NCRP approach suggests that the primary and secondary barrier thicknesses are higher by 24% and 26%. respectively, for a LINAC operated in FF mode to that of a LINAC operated in both FF and FFF modes with an assumption that only 20% of the workload is shared in FFF mode. Primary and secondary barrier thicknesses calculated from MUs delivered on clinical practice method also show the same trend and are higher by 20% and 19%, respectively, for a LINAC operated in FF mode to that of a LINAC operated in both FF and FFF modes. Overall, the barrier thickness for a LINAC operated in FF mode is higher about 20% to that of a LINAC operated in both FF and FFF modes.
计算了配备均整滤过器（FF）和无均整滤过器（FFF）模式运行的6兆伏医用直线加速器（LINAC）主防护层和副防护层的详细结构屏蔽。计算采用了两种方法，一种是使用美国国家辐射防护委员会（NCRP）第151号报告中给出的方法，另一种是基于临床实践中输出的监测单位（MU）。还对这些设施进行了辐射检测。NCRP方法表明，假设在FFF模式下仅分担20%的工作量，与同时运行FF和FFF模式的直线加速器相比，运行FF模式的直线加速器的主防护层和副防护层厚度分别高出24%和26%。根据临床实践方法中输出的监测单位计算得出的主防护层和副防护层厚度也呈现相同趋势，与同时运行FF和FFF模式的直线加速器相比，运行FF模式的直线加速器的主防护层和副防护层厚度分别高出20%和19%。总体而言，运行FF模式的直线加速器的防护层厚度比同时运行FF和FFF模式的直线加速器高出约20%。
