Degree Programs in Comprehensive Human Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Ibaraki, Japan.
Radiation Safety and Quality Assurance division, National Cancer Center Hospital East, Chiba, Japan.
J Appl Clin Med Phys. 2024 Sep;25(9):e14439. doi: 10.1002/acm2.14439. Epub 2024 Jun 20.
Coincidence of the treatment and imaging isocenter coordinates is required to safely perform small-margin treatments, such as stereotactic radiosurgery of multiple brain metastases. A comprehensive and direct methodology for verifying concordance of kilovoltage cone-beam computed tomography (kV-CBCT) and treatment coordinates using an x-ray CT-based polymer gel dosimeter (dGEL) and onboard kV-CBCT was previously reported. Using this methodology, we tested the ability of a new commercially available x-ray CT-based polymer dGEL with a rapid response to provide efficient quality assurance (QA).
The aim of this study was to evaluate the robustness of the three-dimensional geometric QA methodology using dGEL.
The dGEL were commercially manufactured. The prescribed dose for each field was determined by visually identifying the 5, 10, and 20 Gy isodose lines. A linear accelerator was used to irradiate the gels with seven non-coplanar beams. An in-house analysis program was used to identify the beam axes and treatment isocenter in kV-CBCT coordinates by processing the pre- and post-irradiation CBCT images. The impact of the radiation dose on the test reproducibility was examined, and the detectability of an intentional geometric error was assessed.
The treatment isocenter was within 0.4 mm of the imaging isocenter for all radiation doses. The residual error of the test with the intentional error was within 0.2 mm. The analysis and image quality variations for a single dGEL introduced displacement errors less than 0.3 mm.
The test assessed the coincidence of treatment and kV-CBCT isocenter coordinates and detected errors with high robustness. Even for a 10 Gy dose, the test yielded results comparable with those obtained using higher radiation doses owing to the rapid response of the dGEL dosimeter.
为了安全地进行小边缘治疗，如多发脑转移立体定向放射外科，需要治疗和成像等中心坐标重合。以前已经报道了一种使用基于 X 射线的聚合物凝胶剂量计（dGEL）和机载千伏锥形束 CT（kV-CBCT）综合且直接验证千伏锥形束 CT（kV-CBCT）和治疗坐标一致性的方法。使用该方法，我们测试了一种新的商业上可获得的基于 X 射线的快速响应聚合物 dGEL 的三维几何 QA 方法的能力，以提供高效的质量保证（QA）。
本研究的目的是评估使用 dGEL 的三维几何 QA 方法的稳健性。
dGEL 是商业制造的。通过目视识别 5、10 和 20 Gy 等剂量线来确定每个场的规定剂量。使用直线加速器用七个非共面光束照射凝胶。使用内部分析程序通过处理照射前后的 CBCT 图像，在 kV-CBCT 坐标中识别光束轴和治疗等中心。检查了辐射剂量对测试可重复性的影响，并评估了有意几何误差的可检测性。
对于所有辐射剂量，治疗等中心都在成像等中心的 0.4mm 内。具有故意误差的测试的残余误差在 0.2mm 内。单个 dGEL 的分析和图像质量变化会引入小于 0.3mm 的位移误差。
该测试评估了治疗和 kV-CBCT 等中心坐标的一致性，并具有很高的稳健性检测误差。即使对于 10Gy 的剂量，由于 dGEL 剂量计的快速响应，测试也能获得与使用更高辐射剂量相当的结果。
