Department of Radiation Oncology, Division of Medical Physics, University of Iowa Hospitals and Clinics, Iowa City, Iowa 52242
J Appl Clin Med Phys. 2012 Jul 5;13(4):3701. doi: 10.1120/jacmp.v13i4.3701.
The purpose of this study was to report the characteristics of an equivalent quality unflattened (eqUF) photon beam in clinical implementation and to provide a generalized method to describe unflattened (UF) photon beam profiles. An unflattened photon beam with a beam quality equivalent to the corresponding flat 6 MV photon beam (WF) was obtained by removing the flattening filter from a Siemens ONCOR Avant-Garde linear accelerator and adjusting the photon energy. A method independent from the WF beam profile was presented to describe UF beam profiles and other selected beam characteristics were examined. The short-term beam stability was examined by dynamic beam profiles, recorded every 0.072 s in static and gated delivery, and the long-term stability was evidenced by the five-year clinical quality assurance records. The dose rate was raised fivefold using the eqUF beam. The depth of maximum dose (d(max)) shifted 3 mm deeper, but the percent depth dose beyond d(max) was very similar to that of the WF beam. The surface dose and out-of-field dose were lower, but the penumbra was slightly wider. The variation in head scatter and phantom scatter with changes in field size was smaller; the variation in the profile shape with change in depth was also smaller. The eqUF beam is stable 0.072 s after the beam is turned on, and the five-year beam stability was comparable to that of the WF beam. A fivefold dose rate increase was observed in the eqUF beam with similar beam characteristics to other reported UF beam data except for a deeper dmax and a slightly wider penumbra. The initial and long-term stability of the eqUF beam profile is on parity with the WF beam. The UF beam profile can be described in the generalized method independently without relying on the WF beam profile.
本研究的目的是报告等效平坦（eqUF）光子束在临床实施中的特点，并提供一种通用方法来描述非平坦（UF）光子束的轮廓。通过从 Siemens ONCOR Avant-Garde 直线加速器中去除平坦化滤波器并调整光子能量，获得了与相应的平坦 6 MV 光子束（WF）等效质量的非平坦光子束。提出了一种不依赖于 WF 束轮廓的方法来描述 UF 束轮廓，并检查了其他选定的束特性。通过动态束轮廓检查短期束稳定性，在静态和门控输送中每 0.072 秒记录一次，通过五年的临床质量保证记录证明长期稳定性。使用 eqUF 束将剂量率提高了五倍。最大剂量深度（d(max)）加深了 3 毫米，但 d(max)以外的百分深度剂量与 WF 束非常相似。表面剂量和场外剂量较低，但半影稍宽。随着射野大小的变化，头部散射和体模散射的变化较小；随着深度的变化，轮廓形状的变化也较小。在打开光束后的 0.072 秒内，eqUF 束是稳定的，五年的光束稳定性与 WF 束相当。在 eqUF 束中观察到五倍的剂量率增加，其束特性与其他报道的 UF 束数据相似，除了 d(max)更深和半影稍宽之外。eqUF 束的初始和长期稳定性与 WF 束相当。UF 束轮廓可以用通用方法独立描述，而不依赖于 WF 束轮廓。
