Department of Radiation Oncology, Wake Forest School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157, USA.
Radiat Oncol. 2011 Dec 28;6:180. doi: 10.1186/1748-717X-6-180.
This study seeks to increase clinical operational efficiency and accelerator beam consistency by retrospectively investigating the application of statistical process control (SPC) to linear accelerator beam steering parameters to determine the utility of such a methodology in detecting changes prior to equipment failure (interlocks actuated).
Steering coil currents (SCC) for the transverse and radial planes are set such that a reproducibly useful photon or electron beam is available. SCC are sampled and stored in the control console computer each day during the morning warm-up. The transverse and radial - positioning and angle SCC for photon beam energies were evaluated using average and range (Xbar-R) process control charts (PCC). The weekly average and range values (subgroup n = 5) for each steering coil were used to develop the PCC. SCC from September 2009 (annual calibration) until two weeks following a beam steering failure in June 2010 were evaluated. PCC limits were calculated using the first twenty subgroups. Appropriate action limits were developed using conventional SPC guidelines.
PCC high-alarm action limit was set at 6 standard deviations from the mean. A value exceeding this limit would require beam scanning and evaluation by the physicist and engineer. Two low alarms were used to indicate negative trends. Alarms received following establishment of limits (week 20) are indicative of a non-random cause for deviation (Xbar chart) and/or an uncontrolled process (R chart). Transverse angle SCC for 6 MV and 15 MV indicated a high-alarm 90 and 108 days prior to equipment failure respectively. A downward trend in this parameter continued, with high-alarm, until failure. Transverse position and radial angle SCC for 6 and 15 MV indicated low-alarms starting as early as 124 and 116 days prior to failure, respectively.
Radiotherapy clinical efficiency and accelerator beam consistency may be improved by instituting SPC methods to monitor the beam steering process and detect abnormal changes prior to equipment failure.PACS numbers: 87.55n, 87.55qr, 87.56bd.
本研究通过回顾性调查统计过程控制（SPC）在直线加速器束流转向参数中的应用，旨在提高临床运行效率和加速器束流稳定性，以确定该方法在设备故障（联锁启动）前检测变化的实用性。
横向和径向平面的转向线圈电流（SCC）设定为可获得重复性有用的光子或电子束。在早晨预热期间，SCC 每天都会被采样并存储在控制台计算机中。使用平均和极差（Xbar-R）过程控制图（PCC）评估光子束能的横向和径向定位和角度 SCC。每周的平均和极差值（子组 n=5）用于为每个转向线圈开发 PCC。评估了 2009 年 9 月（年度校准）至 2010 年 6 月束流转向故障后两周的 SCC。使用前 20 个子组计算 PCC 的限值。使用传统的 SPC 指南制定适当的行动限值。
PCC 高报警行动限值设定为平均值的 6 个标准差。超过此限值的值将需要物理学家和工程师进行束扫描和评估。使用两个低警报来指示负趋势。建立限值（第 20 周）后收到的警报表明偏差（X 图）和/或不受控制的过程（R 图）存在非随机原因。6 MV 和 15 MV 的横向角度 SCC 分别在设备故障前 90 天和 108 天达到高报警。该参数继续呈下降趋势，直至高报警，直至故障。6 MV 和 15 MV 的横向位置和径向角度 SCC 表明低报警最早分别在故障前 124 天和 116 天开始。
通过实施 SPC 方法来监测束流转向过程并在设备故障前检测异常变化，可能会提高放射治疗的临床效率和加速器束流稳定性。
PACS 编号：87.55n、87.55qr、87.56bd。
