Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY 10065, United States of America.
Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY 10065, United States of America.
Phys Med Biol. 2021 Feb 5;66(4):045020. doi: 10.1088/1361-6560/abd66a.
Current magnetic resonance imaging (MRI) guided radiotherapy (MRgRT) applies sagittal/coronal 2D-cine to monitor major tumor motions, however, the beam eye's view (BEV) with volumetric tumor projection would be the best measure for radiation beam conformality, independent of tumor through-plane motion. The goal is to assess the feasibility, accuracy, and performance of the BEV approach.
Beam-specific BEV 2D-cine with volume-projected tumor contours were simulated to establish a 2D/3D tumor match against a tumor-motion library based on multi-breath time-resolved (TR) 4DMRI images. Two BEV-library-matching methods were developed: (1) fast screening with tumor center-of-mass (∆COM), in-plane area ratio, and DICE similarity, and finalizing with the highest DICE score and (2) DICE screening for top-3 candidates and finalizing with rigid registration. A 4D-XCAT digital phantom and 8 lung-cancer patients were used for assessment. For each patient, 3 sets of 40 s TR-4DMRI were acquired at 2 Hz and 6 representative BEV were created with the isocenter set at tumor COM in mid-respiration. One TR-4DMRI set (40 × 2 = 80-images) was used to simulate BEV 2D-cine and the other two (160-images) were used to create a library. The matching result was validated against the ground truth within the test set. Using a leave-one-out strategy, the success rate, accuracy, and speed of tumor matching were assessed for volume-projected tumors over 11520 time-points (=8patients•3sets•80images•6BEVs).
Volume-projected tumor contour area on the 6 BEVs varies by 60% ± 8% and [Formula: see text] (in-plane/volume-projected) varies by 82% ± 9%. The [Formula: see text] changes with tumor shape, orientation, and through-plane motion. Method-1 produces 96% matching success (ΔCOM = 0.7 ± 0.2 mm, [Formula: see text]=1.01 ± 0.02, Dice=0.92 ± 0.02) with the computational time of 15 ± 1 ms/match, while method-2 produces 94% ± 1% success (ΔCOM = 0.2 ± 0.1 mm, [Formula: see text]=1.00 ± 0.01, Dice = 0.94 ± 0.02) with 223 ± 13 ms/match.
This study has demonstrated the feasibility, accuracy, and benefits of BEV 2D-cine imaging with tumor-volume projection, allowing real-time tumor motion monitoring and beam conformality checking. Further clinical evaluation is necessary before MRgRT applications.
目前的磁共振引导放射治疗（MRgRT）采用矢状/冠状 2D 电影来监测主要肿瘤运动，但容积肿瘤投影的视线（BEV）将是评估射束适形性的最佳方法，与肿瘤的前后运动无关。本研究旨在评估 BEV 方法的可行性、准确性和性能。
通过对多呼吸时间分辨（TR）4D-MRI 图像的肿瘤运动库，模拟了具有容积肿瘤轮廓的特定射束的 BEV 2D 电影，以建立 2D/3D 肿瘤匹配。开发了两种 BEV 库匹配方法：（1）使用肿瘤质心（∆COM）、平面面积比和 DICE 相似度进行快速筛选，最后使用最高的 DICE 评分进行最终确定；（2）对前 3 名候选者进行 DICE 筛选，最后使用刚性配准进行最终确定。使用 4D-XCAT 数字体模和 8 例肺癌患者进行评估。对于每个患者，在 2 Hz 下采集 3 组 40 s TR-4D-MRI，并在呼吸中期将等中心点设置在肿瘤 COM 处以创建 6 个代表性的 BEV。使用一组 TR-4D-MRI（40×2=80 幅图像）来模拟 BEV 2D 电影，而另外两组（160 幅图像）用于创建库。使用测试集内的地面实况验证匹配结果。使用留一法策略，评估了 8 名患者 3 组 80 幅图像 6 个 BEV 共 11520 个时间点（=8 名患者•3 组•80 幅图像•6 个 BEV）上体积投影肿瘤的匹配成功率、准确性和速度。
6 个 BEV 上的容积投影肿瘤轮廓面积变化 60%±8%，[公式：见文本]（平面内/容积投影）变化 82%±9%。[公式：见文本]随肿瘤形状、方向和前后运动而变化。方法 1 产生 96%的匹配成功率（∆COM=0.7±0.2mm，[公式：见文本]=1.01±0.02，Dice=0.92±0.02），计算时间为 15±1ms/次匹配，而方法 2 产生 94%±1%的成功率（∆COM=0.2±0.1mm，[公式：见文本]=1.00±0.01，Dice=0.94±0.02），计算时间为 223±13ms/次匹配。
本研究证明了具有肿瘤容积投影的 BEV 2D 电影成像的可行性、准确性和优势，允许实时肿瘤运动监测和射束适形性检查。在 MRgRT 应用之前，还需要进行进一步的临床评估。
