Nakagawa K, Aoki Y, Akanuma A, Onogi Y, Terahara A, Sakata K, Muta N, Sasaki Y, Kawakami H, Hanakawa K
Department of Radiology, University of Tokyo, Japan.
Int J Radiat Oncol Biol Phys. 1994 Dec 1;30(5):1233-8. doi: 10.1016/0360-3016(94)90334-4.
Although portal imaging is a promising method of verification during static multiport irradiation, it cannot be applied directly to dynamic irradiation such as rotational conformation with multileaf collimator movement. A real-time beam monitoring system based on megavoltage computed tomography scanning has been developed to establish a verification method for the rotational conformation technique.
Exit beam through the patient is extracted by the same detector unit as used for megavoltage scanning during the actual treatment. Beam edge is defined as the 50% level of the maximum dose of the detector array. Megavoltage computed tomography is done after patient setup and just prior to the actual irradiation. Detected beam pathways are overlaid on this image approximately every 1 s. Therapists can monitor correlation between the target and actual beam pathways on a real-time computer display.
The accuracy of field edge detection has been proven to be less than 2 mm from various measurements. Real-time monitoring is more useful in rotational conformation than in static multiport irradiation due to dynamic movement of the collimator. Field errors were identified in two of 54 sessions using this method.
Although several limitations remain to be solved, the method presented is a useful tool for treatment verification of high accuracy radiation therapy, particularly rotational conformation irradiation.
尽管门静脉成像在静态多端口照射期间是一种很有前景的验证方法，但它不能直接应用于动态照射，如带有多叶准直器运动的旋转适形照射。基于兆伏级计算机断层扫描开发了一种实时束流监测系统，以建立旋转适形技术的验证方法。
在实际治疗期间，通过与用于兆伏级扫描相同的探测器单元提取穿过患者的出射束流。束流边缘定义为探测器阵列最大剂量的50%水平。在患者摆位后且在实际照射之前进行兆伏级计算机断层扫描。大约每1秒将检测到的束流路径叠加在该图像上。治疗师可以在实时计算机显示器上监测靶区与实际束流路径之间的相关性。
通过各种测量已证明场边缘检测的精度小于2毫米。由于准直器的动态运动，实时监测在旋转适形中比在静态多端口照射中更有用。使用该方法在54个疗程中有两个疗程发现了野误差。
尽管仍有几个局限性有待解决，但所提出的方法是高精度放射治疗，特别是旋转适形照射治疗验证的有用工具。
