Tanaka Yoshihiro, Mizuno Hirokazu, Akino Yuichi, Isono Masaru, Masai Norimasa, Yamamoto Toshijiro
Department of Radiation Therapy, Japanese Red Cross Society Kyoto Daiichi Hospital, Kyoto-shi, Kyoto, Japan.
Department of Medical Physics and Engineering, Osaka University Graduate School of Medicine, Suita-shi, Osaka, Japan.
J Appl Clin Med Phys. 2019 Feb;20(2):51-62. doi: 10.1002/acm2.12518. Epub 2019 Jan 13.
If the vendor's representative beam data (RBD) for TrueBeam linear accelerators are to be valid for use in clinical practice, the variations in the beam data used for beam modeling must be small. Although a few studies have reported the variation of the beam data of the TrueBeam machines, the numbers of machines analyzed in those studies were small. In this study, we investigated the variation in the beam data for 21 TrueBeam machines collected from 17 institutions with their agreement. In the exponential regions, the percent depth dose (PDD) values showed very small variation, <1% for all the photon energies analyzed. Similarly, the off-center ratio (OCR) values also showed small variation for all energies. In the field regions, the standard deviations of the values of dose difference (DD) between the data for each machine and the study average were <1% for field sizes ≥100 × 100 mm . The maximum distance-to-agreement from the average data was <0.5 mm in the penumbra regions. The output factor (OPF) values also showed very small variation (<1%) for all energies and field sizes. Both the PDD and OCR of the average study data showed good agreement with the vendor's RBD for field sizes ≥100 × 100 mm . The OPF of the average study data also showed good agreement with the vendor's RBD for all field sizes. However, although all the institutions used ionization chambers with similar cavity volumes, the 30 × 30 mm field size showed large DD variations (≥2%) in OCR in the field regions. We conclude that the intermachine variability of TrueBeam linear accelerators was very small except for small field dosimetry, supporting the validity of the use of the RBD for clinical applications. The use of the vendor's RBD might greatly facilitate the quick installation of a new linear accelerator.
如果瓦里安TrueBeam直线加速器的供应商代表束流数据（RBD）要在临床实践中有效使用，用于束流建模的束流数据变化必须很小。尽管有一些研究报告了TrueBeam机器束流数据的变化，但这些研究中分析的机器数量较少。在本研究中，我们调查了从17家机构收集的21台TrueBeam机器的束流数据变化，这些机构均表示同意。在指数区，百分深度剂量（PDD）值变化非常小，对于所有分析的光子能量均<1%。同样，离轴比（OCR）值在所有能量下变化也很小。在射野区，对于射野尺寸≥100×100 mm的情况，每台机器的数据与研究平均值之间的剂量差（DD）值的标准差<1%。在半值层区，与平均数据的最大距离一致性<0.5 mm。输出因子（OPF）值在所有能量和射野尺寸下变化也非常小（<1%）。对于射野尺寸≥100×100 mm，平均研究数据的PDD和OCR与供应商的RBD均显示出良好的一致性。平均研究数据的OPF在所有射野尺寸下与供应商的RBD也显示出良好的一致性。然而，尽管所有机构都使用了腔体积相似的电离室，但在射野区，30×30 mm射野尺寸的OCR显示出较大的DD变化（≥2%）。我们得出结论，除小射野剂量学外，TrueBeam直线加速器的机器间变异性非常小，这支持了RBD用于临床应用的有效性。使用供应商的RBD可能会极大地促进新直线加速器的快速安装。
