Abstract：
OBJECTIVE: Target positions should be acquired during beam delivery for accurate lung stereotactic body radiotherapy. We aimed to perform kilovoltage (kV) imaging during beam irradiation (intra-irradiation imaging) under phase-gated conditions and evaluate its performance.
METHODS: Catphan 504 and QUASAR respiratory motion phantoms were used to evaluate image quality and target detectability, respectively. TrueBeam STx linac and the Developer Mode was used. The imaging parameters were 125 kVp and 1.2 mAs/projection. Flattened megavoltage (MV) X-ray beam energies 6, 10 and 15 MV and un-flattened beam energies 6 and 10 MV were used with field sizes of 5 × 5 and 15 × 15 cm2 and various frame rates for intra-irradiation imaging. In addition, using a QUASAR phantom, intra-irradiation imaging was performed during intensity-modulated plan delivery. The root-mean-square error (RMSE) of the CT-number for the inserted rods, image noise, visual assessment, and contrast-to-noise ratio (CNR) were evaluated.
RESULTS: The RMSEs of intra-irradiation cone-beam computed tomography (CBCT) images under gated conditions were 50-230 Hounsfield Unit (HU) (static < 30 HU). The noise of the intra-irradiation CBCT images under gated conditions was 15-35 HU, whereas that of the standard CBCT images was 8.8-27.2 HU. Lower frame rates exhibited large RMSEs and noise; however, the iterative reconstruction algorithm (IR) was effective at improving these values. Approximately 7 fps with the IR showed an equivalent CNR of 15 fps without the IR. The target was visible on all the gated intra-irradiation CBCT images.
CONCLUSIONS: Several image quality improvements are required; however, intra-irradiated CBCT images showed good visual target detection.
METHODS: Catphan 504 and QUASAR respiratory motion phantoms were used to evaluate image quality and target detectability, respectively. TrueBeam STx linac and the Developer Mode was used. The imaging parameters were 125 kVp and 1.2 mAs/projection. Flattened megavoltage (MV) X-ray beam energies 6, 10 and 15 MV and un-flattened beam energies 6 and 10 MV were used with field sizes of 5 × 5 and 15 × 15 cm2 and various frame rates for intra-irradiation imaging. In addition, using a QUASAR phantom, intra-irradiation imaging was performed during intensity-modulated plan delivery. The root-mean-square error (RMSE) of the CT-number for the inserted rods, image noise, visual assessment, and contrast-to-noise ratio (CNR) were evaluated.
RESULTS: The RMSEs of intra-irradiation cone-beam computed tomography (CBCT) images under gated conditions were 50-230 Hounsfield Unit (HU) (static < 30 HU). The noise of the intra-irradiation CBCT images under gated conditions was 15-35 HU, whereas that of the standard CBCT images was 8.8-27.2 HU. Lower frame rates exhibited large RMSEs and noise; however, the iterative reconstruction algorithm (IR) was effective at improving these values. Approximately 7 fps with the IR showed an equivalent CNR of 15 fps without the IR. The target was visible on all the gated intra-irradiation CBCT images.
CONCLUSIONS: Several image quality improvements are required; however, intra-irradiated CBCT images showed good visual target detection.
摘要：
目的：为了精确的肺部立体定向放射治疗，应在束传递过程中获取目标位置。我们旨在在相位门控条件下在光束辐照（辐照内成像）期间进行千伏（kV）成像，并评估其性能。
方法：使用Catphan504和QUASAR呼吸运动体模评估图像质量和目标可检测性，分别。使用了TrueBeamSTx直线加速器和开发者模式。成像参数为125kVp和1.2mAs/投影。使用平坦的兆伏（MV）X射线束能量6、10和15MV以及未平坦的束能量6和10MV，场大小为5×5和15×15cm2，并且具有各种帧速率，用于照射内成像。此外,使用量子幻影，在调强计划实施期间进行照射内成像.插入杆的CT数的均方根误差(RMSE)，图像噪声,视觉评估，和对比噪声比（CNR）进行了评估。
结果：门控条件下辐照内锥形束计算机断层扫描（CBCT）图像的RMSE为50-230Hounsfield单位（HU）（静态<30HU）。门控条件下照射内CBCT图像的噪声为15-35HU，而标准CBCT图像为8.8-27.2HU。较低的帧速率表现出较大的RMSE和噪声；然而，迭代重建算法(IR)在改善这些值方面是有效的。具有IR的大约7fps显示出没有IR的15fps的等效CNR。目标在所有门控照射内CBCT图像上可见。
结论：需要改善图像质量；然而，照射内CBCT图像显示良好的视觉目标检测。
方法：使用Catphan504和QUASAR呼吸运动体模评估图像质量和目标可检测性，分别。使用了TrueBeamSTx直线加速器和开发者模式。成像参数为125kVp和1.2mAs/投影。使用平坦的兆伏（MV）X射线束能量6、10和15MV以及未平坦的束能量6和10MV，场大小为5×5和15×15cm2，并且具有各种帧速率，用于照射内成像。此外,使用量子幻影，在调强计划实施期间进行照射内成像.插入杆的CT数的均方根误差(RMSE)，图像噪声,视觉评估，和对比噪声比（CNR）进行了评估。
结果：门控条件下辐照内锥形束计算机断层扫描（CBCT）图像的RMSE为50-230Hounsfield单位（HU）（静态<30HU）。门控条件下照射内CBCT图像的噪声为15-35HU，而标准CBCT图像为8.8-27.2HU。较低的帧速率表现出较大的RMSE和噪声；然而，迭代重建算法(IR)在改善这些值方面是有效的。具有IR的大约7fps显示出没有IR的15fps的等效CNR。目标在所有门控照射内CBCT图像上可见。
结论：需要改善图像质量；然而，照射内CBCT图像显示良好的视觉目标检测。
