Intensity modulated radiation therapy (IMRT) is a highly accurate technique that is usually implemented in either dynamic or step-and-shoot fashion with many segments each having low monitor units (MUs). The present s...Intensity modulated radiation therapy (IMRT) is a highly accurate technique that is usually implemented in either dynamic or step-and-shoot fashion with many segments each having low monitor units (MUs). The present study evaluated the effects of beam startup characteristics on the dose delivery accuracy for each segment at low MUs for step-and-shoot IMRT with an Elekta Precise accelerator at the highest dose rates. We used a two-dimensional semi-conductor detector for the dose measurements. The field size of each segment was assumed to be 20 ×20 cm2 and each segment was set to deliver 1 - 10 MUs. Our results show a variation in dose delivery accuracy between segments for the same IMRT beam, which can be attributed to the beam startup characteristics. This variability is attributed to the changes in the transient changes in the temperatures of the electron gun filament and the magnetron. That is, the transient increase in the temperature of the filament leads to increasing doses with time and that of the magnetron leads to decreasing doses with time during the first few MUs.展开更多
The stability of delivery of low monitor unit (MU) setting is important especially for step-and-shoot intensity-modulated radiotherapy (IMRT), because the nature of the technique is inherent to repeat beam on/off acco...The stability of delivery of low monitor unit (MU) setting is important especially for step-and-shoot intensity-modulated radiotherapy (IMRT), because the nature of the technique is inherent to repeat beam on/off according to the number of the segments. This study evaluates the dose linearity and profile flatness/symmetry under low MU settings for Vero4DRT, a new linear-accelerator based irradiation system that currently implements step-and-shoot IMRT. To evaluate the dose linearity and flatness/symmetry, the point doses and beam profiles were measured as functions of MU and dose rates. The accuracy of dose delivery depended on the dose rate. Under all dose rates, the dose was linear within 1% above 5 MU and within 2% above 3 MU. The beam symmetry was degraded in-line compared with crossline, although both profiles were symmetric within 2% at all dose settings. The profile flatness was also within 2% above 5 MU at any dose rate and showed no significant variation among the low MU settings. To ensure stable beam delivery without increasing the treatment time of Vero4DRT, we recommend a delivery of 5 MU per segment at a dose rate of 500 MU/min.展开更多
广域测量系统(wide area monitoring system,WAMS)的发展为电力系统低频振荡在线辨识奠定了基础。WAMS采集的信号含有高斯白噪声,经低通滤波处理后会产生高斯色噪声,因此会对模式识别的准确性产生不利影响。针对这一问题,提出以实测信...广域测量系统(wide area monitoring system,WAMS)的发展为电力系统低频振荡在线辨识奠定了基础。WAMS采集的信号含有高斯白噪声,经低通滤波处理后会产生高斯色噪声,因此会对模式识别的准确性产生不利影响。针对这一问题,提出以实测信号的四阶混合平均累计量(fourth-order mixed mean cumulant,FOMMC)的对角切片来代替实测信号,并结合矩阵束(matrix pencil,MP)算法对振荡模式进行识别的方法。仿真结果表明,FOMMC-MP算法能够有效从色噪声环境中辨识出系统主导模态。展开更多
针对目前低压配电网线损统计对数据的准确性和实时性等要求,提出并实现了一种基于全球移动通信系统GSM(Global System for Mobile Communication),利用监测终端装置所采集的数据进行实时计算低压配网线损功率的在线监测系统。该系统能...针对目前低压配电网线损统计对数据的准确性和实时性等要求,提出并实现了一种基于全球移动通信系统GSM(Global System for Mobile Communication),利用监测终端装置所采集的数据进行实时计算低压配网线损功率的在线监测系统。该系统能适应弱环网等复杂的配网运行方式,并能快速准确地计算出低压配网中每条馈线的功率损耗情况,为低压配网线损的分析与管理提供可靠的基础。着重介绍了该线损监测系统的原理和总体结构。此外,还给出了终端监测装置的硬件整体实现方案和软件设计思想。展开更多
文摘Intensity modulated radiation therapy (IMRT) is a highly accurate technique that is usually implemented in either dynamic or step-and-shoot fashion with many segments each having low monitor units (MUs). The present study evaluated the effects of beam startup characteristics on the dose delivery accuracy for each segment at low MUs for step-and-shoot IMRT with an Elekta Precise accelerator at the highest dose rates. We used a two-dimensional semi-conductor detector for the dose measurements. The field size of each segment was assumed to be 20 ×20 cm2 and each segment was set to deliver 1 - 10 MUs. Our results show a variation in dose delivery accuracy between segments for the same IMRT beam, which can be attributed to the beam startup characteristics. This variability is attributed to the changes in the transient changes in the temperatures of the electron gun filament and the magnetron. That is, the transient increase in the temperature of the filament leads to increasing doses with time and that of the magnetron leads to decreasing doses with time during the first few MUs.
文摘The stability of delivery of low monitor unit (MU) setting is important especially for step-and-shoot intensity-modulated radiotherapy (IMRT), because the nature of the technique is inherent to repeat beam on/off according to the number of the segments. This study evaluates the dose linearity and profile flatness/symmetry under low MU settings for Vero4DRT, a new linear-accelerator based irradiation system that currently implements step-and-shoot IMRT. To evaluate the dose linearity and flatness/symmetry, the point doses and beam profiles were measured as functions of MU and dose rates. The accuracy of dose delivery depended on the dose rate. Under all dose rates, the dose was linear within 1% above 5 MU and within 2% above 3 MU. The beam symmetry was degraded in-line compared with crossline, although both profiles were symmetric within 2% at all dose settings. The profile flatness was also within 2% above 5 MU at any dose rate and showed no significant variation among the low MU settings. To ensure stable beam delivery without increasing the treatment time of Vero4DRT, we recommend a delivery of 5 MU per segment at a dose rate of 500 MU/min.
文摘广域测量系统(wide area monitoring system,WAMS)的发展为电力系统低频振荡在线辨识奠定了基础。WAMS采集的信号含有高斯白噪声,经低通滤波处理后会产生高斯色噪声,因此会对模式识别的准确性产生不利影响。针对这一问题,提出以实测信号的四阶混合平均累计量(fourth-order mixed mean cumulant,FOMMC)的对角切片来代替实测信号,并结合矩阵束(matrix pencil,MP)算法对振荡模式进行识别的方法。仿真结果表明,FOMMC-MP算法能够有效从色噪声环境中辨识出系统主导模态。
文摘针对目前低压配电网线损统计对数据的准确性和实时性等要求,提出并实现了一种基于全球移动通信系统GSM(Global System for Mobile Communication),利用监测终端装置所采集的数据进行实时计算低压配网线损功率的在线监测系统。该系统能适应弱环网等复杂的配网运行方式,并能快速准确地计算出低压配网中每条馈线的功率损耗情况,为低压配网线损的分析与管理提供可靠的基础。着重介绍了该线损监测系统的原理和总体结构。此外,还给出了终端监测装置的硬件整体实现方案和软件设计思想。
