An end-to-end examination of geometric accuracy of IGRT using a new digital accelerator equipped with onboard imaging system.
An end-to-end examination of geometric accuracy of IGRT using a new digital accelerator equipped with onboard imaging system.
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DOI：
10.1088/0031-9155/57/3/757
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发表时间：
2012-02-07
影响因子：
3.5
通讯作者：
Xing L
中科院分区：
文献类型：
--
作者：
Wang L;Kielar KN;Mok E;Hsu A;Dieterich S;Xing L
瓦里安的新型数字直线加速器TrueBeam™STx配备了高剂量率无滤波平坦（FFF）模式（6 MV和10 MV）、高清多叶准直器（HDMLC） （2.5 mm叶宽）以及机载成像（OBI）功能。基于truebeam的IGRT进行了一系列端到端幻影测试，以确定使用IMRT和RapidArc™提供的所有光束模式的图像引导设置和剂量传递过程的几何精度。在这些测试中，使用带有Ball Cube II插入物的拟人化假体和分析软件（FilmQA™（3cognition））来评估TrueBeam™图像引导设置和给药的准确性。将精度为0.15 mm的激光切割EBT2薄膜嵌入到模体中。首先用GE Discovery-ST CT扫描仪扫描插入薄膜的假体，然后将图像导入规划系统。使用RapidArc和IMRT与FFF和WFF（带平坦滤波）光束创建了不同大小的假设目标周围的陡峭剂量下降计划。研究了4种RapidArc计划（6 MV和10 MV FFF）和5种IMRT计划（6 MV和10 MV FFF； 6 MV， 10 MV和15 MV WFF）。6 MV FFF的RapidArc计划的目标直径为1cm （0.52 cc）、2cm （4.2 cc）和3cm (14.1 cc)，所有其他计划的目标直径为3cm。机载平面和体积成像程序都用于幻影设置和目标定位。然后提供IMRT和RapidArc计划，并使用3%/1 mm和3%/2 mm的Gamma标准将膜测量值与原始治疗计划进行比较。为了使薄膜测量剂量与计算剂量分布对齐所需的位移归因于靶向误差。使用TrueBeam™的图像引导治疗的靶向精度在1mm以内。对于照射3cm靶，在所有计划交付中，伽玛（3%,1mm）均高于90%。对于较小的目标（2厘米和1厘米），6毫伏和10毫伏光束的照射精度相似。在高能光束（15 MV）照射下，精度略有下降。总的来说，伽玛（3%,2mm）在所有方案中都高于97%。我们的端到端测试显示，使用FFF和WFF两种传输方式，对于6和10 MV光束，具有出色的相对剂量学一致性和亚毫米瞄准精度。然而，当治疗小于2 cm的病变或使用15 MV波束时，发现空间和剂量准确性的偏差增加。
The Varian’s new digital linear accelerator (LINAC), TrueBeam™ STx, is equipped with high dose rate flattening filter free (FFF) mode (6 MV and 10 MV), high definition multileaf collimator (HDMLC) (2.5 mm leaf width), as well as onboard imaging (OBI) capabilities. A series of end-to-end phantom tests were performed TrueBeam-based IGRT to determine the geometric accuracy of image-guided setup and dose delivery process for all beam modalities delivered using IMRT and RapidArc™. In these tests, an anthropomorphic phantom with a Ball Cube II insert and the analysis software (FilmQA™ (3cognition)) were used to evaluate the accuracy of TrueBeam™ image-guided setup and dose delivery. Laser cut EBT2 films with 0.15 mm accuracy were embedded into the phantom. The phantom with the film inserted was first scanned with a GE Discovery-ST CT scanner, and the images were then imported to the planning system. Plans with steep dose fall off surrounding hypothetical targets of different sizes were created using RapidArc and IMRT with FFF and WFF (with flattening filter) beams. Four RapidArc plans (6 MV and 10 MV FFF) and five IMRT plans (6 MV and 10 MV FFF; 6 MV, 10 MV and 15 MV WFF) were studied. The RapidArc plans with 6 MV FFF were planned with target diameters of 1 cm (0.52 cc), 2 cm (4.2 cc), and 3 cm (14.1 cc), and all other plans were planned with a target diameter of 3 cm. Both onboard planar and volumetric imaging procedures were used for phantom setup and target localization. The IMRT and RapidArc plans were then delivered, and the film measurements were compared with the original treatment plans using a Gamma criteria of 3%/1 mm and 3%/2 mm. The shifts required in order to align the film measured dose with the calculated dose distributions was attributed to be the targeting error. Targeting accuracy of image-guided treatment using TrueBeam™ was found to be within 1 mm. For irradiation of the 3 cm target, the Gammas (3%, 1 mm) were found to be above 90% in all plan deliveries. For irradiations of smaller targets (2 cm and 1 cm), similar accuracy was achieved for 6 MV and 10 MV beams. Slightly degraded accuracy was observed for irradiations with higher energy beam (15 MV). In general, Gammas (3%, 2 mm) were found to be above 97% for all the plans. Our end-to-end tests showed an excellent relative dosimetric agreement and sub millimeter targeting accuracy for 6 and 10 MV beams, using both FFF and WFF delivery methods. However, increased deviations in spatial and dosimetric accuracy were found when treating lesions smaller than 2 cm or with 15 MV beam.