Fogliata Antonella, Fleckenstein Jens, Schneider Frank, Pachoud Marc, Ghandour Sarah, Krauss Harald, Reggiori Giacomo, Stravato Antonella, Lohr Frank, Scorsetti Marta, Cozzi Luca
Radiotherapy and Radiosurgery Department, Humanitas Research Hospital, Milan-Rozzano I-20098, Italy.
Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Mannheim D-68167, Germany.
Med Phys. 2016 Jan;43(1):205. doi: 10.1118/1.4938060.
Flattening filter free (FFF) beams generated by medical linear accelerators are today clinically used for stereotactical and non-stereotactical radiotherapy treatments. Such beams differ from the standard flattened beams (FF) in the high dose rate and the profile shape peaked on the beam central axis. Definition of new parameters as unflatness and slope for FFF beams has been proposed based on a renormalization factor for FFF profiles. The present study aims to assess the dosimetric differences between FFF beams generated by linear accelerators from different vendors, and to provide renormalization and parameter data of the two kinds of units.
Dosimetric data from two Varian TrueBeam and two Elekta Versa HD linear accelerators, all with 6 and 10 MV nominal accelerating potentials, FF and FFF modes have been collected. Renormalization factors and related fit parameters according to Fogliata et al. ["Definition of parameters for quality assurance of flattening filter free (FFF) photon beams in radiation therapy," Med. Phys. 39, 6455-6464 (2012)] have been evaluated for FFF beams of both units and energies. Unflatness and slope parameters from profile curves were evaluated. Dosimetric differences in terms of beam penetration and near-the-surface dose were also assessed.
FFF profile parameters have been updated; renormalization factors and unflatness from the Varian units are consistent with the published data. Elekta FFF beam qualities, different from the Varian generated beams, tend to express similar behaviour as the FF beam of the corresponding nominal energy. TPR20,10 for 6 and 10 MV FF and FFF TrueBeam beams are 0.665, 0.629 (6 MV) and 0.738, 0.703 (10 MV). The same figures for Versa HD units are 0.684, 0.678 (6 MV) and 0.734, 0.721 (10 MV).
Renormalization factor and unflatness parameters evaluated from Varian and Elekta FFF beams are provided, in particular renormalization factors table and fit parameters.
如今，医用直线加速器产生的无均整器（FFF）束流在立体定向和非立体定向放射治疗中得到了临床应用。此类束流与标准均整束流（FF）不同，具有高剂量率且在束流中心轴上剂量分布呈峰值状。基于FFF剂量分布的归一化因子，有人提出了FFF束流的新参数，如不均整度和斜率。本研究旨在评估不同厂家生产的直线加速器所产生的FFF束流之间的剂量学差异，并提供这两种设备的归一化和参数数据。
收集了两台瓦里安TrueBeam和两台医科达Versa HD直线加速器的剂量学数据，所有加速器的标称加速电位均为6和10 MV，具备FF和FFF模式。根据Fogliata等人的研究[《放射治疗中无均整器（FFF）光子束质量保证参数的定义》，《医学物理》39, 6455 - 6464（2012）]，对两台设备两种能量的FFF束流评估了归一化因子及相关拟合参数。对剂量分布曲线的不均整度和斜率参数进行了评估。还评估了束流穿透和表面附近剂量方面的剂量学差异。
更新了FFF剂量分布参数；瓦里安设备的归一化因子和不均整度与已发表数据一致。医科达FFF束流特性与瓦里安产生的束流不同，其表现出与相应标称能量的FF束流相似的行为。6和10 MV的FF和FFF TrueBeam束流的组织空气比TPR20,10分别为0.665、0.629（6 MV）和0.738、0.703（10 MV）。Versa HD设备的相应数值为0.684、0.678（6 MV）和0.734、0.721（10 MV）。
给出了从瓦里安和医科达FFF束流评估得到的归一化因子和不均整度参数，特别是归一化因子表和拟合参数。
