Bhangle Janhavi R, Sathiya Narayanan V K, Deshpande Shrikant A
Department of Radiation Oncology, Ruby Hall Clinic, Pune, India.
J Med Phys. 2007 Jul;32(3):103-7. doi: 10.4103/0971-6203.35722.
For step-and-shoot type delivery of intensity-modulated radiation therapy (IMRT), beam stability characteristics during the first few monitor units need to be investigated to ensure the planned dose delivery. This paper presents the study done for Siemens ONCOR impression plus linear accelerator before commissioning it for IMRT treatment. The beam stability for 6 and 15 MV in terms of dose monitor linearity, monitor unit stability and beam uniformity is investigated in this work. Monitor unit linearity is studied using FC65G chamber for the range 1-100 MU. The dose per MU is found to be linear for small monitor units down to 1 MU for both 6 and 15 MV beams. The monitor unit linearity is also studied with portal imaging device for the range 1-20 MU for 6 MV beam. The pixel values are within ±1σ confidence level up to 2 MU; for 1 MU, the values are within ±2σ confidence level. The flatness and symmetry analysis is done for both energies in the range of 1-10 MU with Kodak diagnostic films. The flatness and symmetry are found to be within ±3% up to 2 MU for 6 MV and up to 3 MU for 15 MV.
对于调强放射治疗（IMRT）的步进-射野式照射，需要研究最初几个监测单位期间的射束稳定性特征，以确保计划的剂量传递。本文介绍了在西门子ONCOR impression plus直线加速器投入IMRT治疗调试之前所做的研究。在这项工作中，研究了6兆伏和15兆伏射束在剂量监测线性、监测单位稳定性和射束均匀性方面的射束稳定性。使用FC65G电离室研究了1至100监测单位范围内的监测单位线性。对于6兆伏和15兆伏射束，发现对于低至1监测单位的小监测单位，每监测单位的剂量呈线性。还使用门静脉成像设备研究了6兆伏射束在1至20监测单位范围内的监测单位线性。像素值在高达2监测单位时处于±1σ置信水平内；对于1监测单位，值处于±2σ置信水平内。使用柯达诊断胶片对两种能量在1至10监测单位范围内进行了平坦度和对称性分析。发现对于6兆伏，高达2监测单位时平坦度和对称性在±3%以内；对于15兆伏，高达3监测单位时平坦度和对称性在±3%以内。
