Purpose/Objective(s)

The precise radiomics analysis on thoracic 4DCT data is easily compromised by the respiratory motion and CT scan parameter setting, thus leading to the risk of overfitting and/or misinterpretation of data in AI-enabled therapeutic model building. In this study, we investigated the impact of respiratory amplitudes, frequencies and CT scan pitch settings within the thoracic 4DCT scan on robust radiomics feature selection.

Materials/Methods

A Three-dimensional QUSAR^TM lung tumor phantom was used to simulate different respiratory amplitudes and frequencies along with different CT scan pitch settings. A total of 43 tumor respiratory patterns extracted from 43 patients with non-small cell lung cancer were used to drive the QUSAR^TM lung tumor phantom to mimic the human tumor motion. The 4DCT images of the QUSAR^TM lung tumor phantom with different respiratory patterns and different CT scan pitch setups were acquired for radiomics feature extraction. A static high-quality CT images of the phantom acquired were also used as a reference for radiomics feature extraction. The range of respiratory amplitudes was mimicked at 3mm at left and right (LR) and anterior and posterior (AP) directions and 3mm - 15 mm at the superior and inferior (SI) direction with an interval of 2 mm. The respiratory frequencies were set at 10, 11, 12, 13, 14, 15 and 20 beats per minute (BPMs), respectively. The CT scan pitches were set at 0.025, 0.048, 0.071, 0.93, 0.108, 0.14, 0.16, 0.18, 0.21, 0.23, and 0.25, respectively, which was based on a procedure described in Med. Phys. 30(1):88-97. The pairwise Concordance Correlation Coefficient (CCC) was used to determine the robustness of radiomics feature extraction via comparing the agreement in feature values between 1766 radiomics features extracted from each image acquired under different combinations of respiratory amplitudes and frequencies and CT scan pitches of 4DCT and those extracted from the static CT images.

Results

(1) When the respiratory amplitudes were at 3, 5, 7, 9, 12 and 15mm in the SI direction, the maximum CCC index could be achieved at the reconstructed 4DCT phase images of 60%, 70%, 30%, 20%, 60%~70% and 10%, respectively. Under these six amplitudes, the maximum intensity projection (MIP) and average intensity projection (AIP) images reconstructed show mean CCC values of 0.778 and 0.609, respectively, in pairwise radiomics feature extraction comparison between 4DCT and static CT. (2) When the respiratory amplitude was set at 12 mm in the SI direction, the maximum CCC index could be consistently achieved at the reconstructed 4DCT phase of 90% for the seven respiratory frequencies of 10, 11, 12, 13, 14, 15 and 20 BPMs, respectively. Under these respiratory states, the MIP and AIP images reconstructed show mean CCC values of 0.702 and 0.562, respectively. (3) When the respiratory amplitude was set at 12 mm and the respiratory frequency was set at 13 BPM, the maximum CCC index could be obtained at the reconstructed 4DCT phase of 90% for all scan pitches used except the 0% phase which was obtained at the pitch setting of 0.048. Under these CT scan pitch settings, the MIP and AIP images reconstructed show mean CCC values of 0.558 and 0.782, respectively. (4) The total number of robust features were 50, 34 and 35 with different respiratory amplitudes and phases and CT scanning pitch used (CCC values ≥ 0.99).

Conclusion

In 4DCT, the respiratory amplitude, frequency and CT scan pitch are three limiting factors that greatly affect the robustness of radiomics feature extraction. The reconstructed 4DCT phases with better robustness along with suitable respiratory amplitude, frequency and CT scan pitch determined could be used to guide the breathing training for patients with lung cancer for radiation therapy to improve the robust radiomics feature extraction process.

中文翻译：

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呼吸运动和 CT 俯仰对 4DCT 肺部成像中放射组学特征提取鲁棒性的影响。

目的/目标

对胸部 4DCT 数据的精确放射组学分析很容易受到呼吸运动和 CT 扫描参数设置的影响，从而导致人工智能治疗模型构建中数据过度拟合和/或误解的风险。在这项研究中，我们调查了胸部 4DCT 扫描中呼吸幅度、频率和 CT 扫描间距设置对稳健放射组学特征选择的影响。

材料/方法

三维 QUSAR ^TM肺肿瘤体模用于模拟不同的呼吸幅度和频率以及不同的 CT 扫描间距设置。从 43 名非小细胞肺癌患者中提取的总共 43 种肿瘤呼吸模式用于驱动 QUSAR ^TM肺肿瘤模型以模拟人类肿瘤运动。QUSAR ^{TM的 4DCT 图像}获得具有不同呼吸模式和不同CT扫描间距设置的肺肿瘤体模用于放射组学特征提取。获得的体模的静态高质量 CT 图像也被用作放射组学特征提取的参考。呼吸幅度的范围在左右（LR）和前后（AP）方向模拟为3mm，在上下（SI）方向模拟为3mm - 15mm，间隔为2mm。呼吸频率分别设置为每分钟 10、11、12、13、14、15 和 20 次 (BPM)。CT 扫描间距分别设置为 0.025、0.048、0.071、0.93、0.108、0.14、0.16、0.18、0.21、0.23 和 0.25，其基于 Med. 物理。30（1）：88-97。

结果

(1)当呼吸幅度在SI方向3、5、7、9、12和15mm时，在重建的4DCT相位图像60%、70%、30%、20%时可以达到最大CCC指数，分别为 60%~70% 和 10%。在这六个振幅下，在 4DCT 和静态 CT 之间的成对放射组学特征提取比较中，重建的最大强度投影 (MIP) 和平均强度投影 (AIP) 图像的平均 CCC 值分别为 0.778 和 0.609。(2) 当呼吸幅度在SI方向设置为12 mm时，10、11、12、13、14、15这7个呼吸频率在重构的4DCT相位90%时可以一致地达到最大CCC指数和 20 BPM，分别。在这些呼吸状态下，重建的 MIP 和 AIP 图像显示平均 CCC 值分别为 0.702 和 0.562，分别。(3) 当呼吸幅度设置为 12 mm，呼吸频率设置为 13 BPM 时，除获得的 0% 相位外，所有使用的扫描间距在 90% 的重建 4DCT 相位处均可获得最大 CCC 指数螺距设置为 0.048。在这些 CT 扫描间距设置下，重建的 MIP 和 AIP 图像显示平均 CCC 值分别为 0.558 和 0.782。(4) 使用不同呼吸幅度和相位以及CT扫描间距的鲁棒特征总数为50、34和35(CCC值≥0.99)。在这些 CT 扫描间距设置下，重建的 MIP 和 AIP 图像显示平均 CCC 值分别为 0.558 和 0.782。(4) 使用不同呼吸幅度和相位以及CT扫描间距的鲁棒特征总数为50、34和35(CCC值≥0.99)。在这些 CT 扫描间距设置下，重建的 MIP 和 AIP 图像显示平均 CCC 值分别为 0.558 和 0.782。(4) 使用不同呼吸幅度和相位以及CT扫描间距的鲁棒特征总数为50、34和35(CCC值≥0.99)。

结论

在 4DCT 中，呼吸幅度、频率和 CT 扫描间距是三个限制因素，极大地影响了放射组学特征提取的鲁棒性。重建的具有更好鲁棒性的 4DCT 相位以及确定的合适的呼吸幅度、频率和 CT 扫描间距可用于指导肺癌患者进行放射治疗的呼吸训练，以改进鲁棒的放射组学特征提取过程。