Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, 77030, USA.
Med Phys. 2018 Feb;45(2):875-883. doi: 10.1002/mp.12695. Epub 2017 Dec 22.
Y-microsphere selective internal radiation therapy ( Y-SIRT or Y-radioembolization) is used in the management of unresectable liver tumors. Y-SIRT presents a unique situation where the total Y activity inside the liver can be determined with high accuracy (> 95%). Y bremsstrahlung single-photon emission computed tomography (SPECT)/computed tomography (CT) can be self-calibrated to provide quantitative images that facilitate voxel-level absorbed dose calculations. We investigated the effects of different approaches for Y-SPECT self-calibration on the quantification of absorbed doses following Y-SIRT.
Y bremsstrahlung SPECT/CT images of 31 patients with hepatocellular carcinoma, collected following Y-SIRT, were analyzed, yielding 48 tumor and 31 normal liver contours. We validated the accuracy of absorbed doses calculated by a commercial software against those calculated using Monte Carlo-based radiation transport. The software package was used to analyze the following definitions of SPECT volume of interest used for Y-SPECT self-calibration: (a) SPECT field-of-view (FOV), (b) chest-abdomen contour, (c) total liver contour, (d) total liver contour expanded by 5 mm, and (e) total liver contour contracted by 5 mm. Linear correlation and Bland-Altman analysis were performed for tumor and normal liver tissue absorbed dose volume histogram metrics between the five different approaches for Y-SPECT self-calibration.
The mean dose calculated using the commercial software was within 3% of Monte Carlo for tumors and normal liver tissues. The tumor mean dose calculated using the chest-abdomen calibration was within 2% of that calculated using the SPECT FOV, whereas the doses calculated using the total liver contour, expanded total liver contour, and contracted total liver contour were within 68%, 47%, and 107%, respectively, of doses calculated using the SPECT FOV. The normal liver tissue mean dose calculated using the chest-abdomen contour was within 1.3% of that calculated using the SPECT FOV, whereas the doses calculated using the total liver contour, expanded total liver contour, and contracted total liver contour were within 73%, 50%, and 114%, respectively, of doses calculated using the SPECT FOV.
The mean error of < 3% for commercial software can be considered clinically acceptable for Y-SIRT dosimetry. Absorbed dose quantification using Y-SPECT self-calibration with the chest-abdomen contour was equivalent to that calculated using the SPECT FOV, but self-calibration with the total liver contour yielded substantially higher (~70%) dose values. The large biases revealed by our study suggest that consistent absorbed dose calculation approaches are essential when comparing Y-SIRT dosimetry between different clinical studies.
Y-微球选择性内放射治疗（Y-SIRT 或 Y-放射性栓塞）用于不可切除的肝脏肿瘤的治疗。Y-SIRT 呈现出一种独特的情况，即可以高精度（>95%）确定肝脏内的总 Y 活性。Y 韧致辐射单光子发射计算机断层扫描（SPECT）/计算机断层扫描（CT）可以自我校准，提供便于体素水平吸收剂量计算的定量图像。我们研究了不同的 Y-SPECT 自我校准方法对 Y-SIRT 后吸收剂量量化的影响。
对 31 例肝细胞癌患者接受 Y-SIRT 后的 Y 韧致辐射 SPECT/CT 图像进行分析，得出 48 个肿瘤和 31 个正常肝脏轮廓。我们验证了商业软件计算的吸收剂量的准确性，与基于蒙特卡罗辐射输运的吸收剂量计算结果相比较。使用软件包分析了用于 Y-SPECT 自我校准的以下 SPECT 感兴趣区定义：（a）SPECT 视野（FOV），（b）胸部-腹部轮廓，（c）总肝轮廓，（d）扩展 5mm 的总肝轮廓，以及（e）收缩 5mm 的总肝轮廓。对五种不同的 Y-SPECT 自我校准方法进行线性相关性和 Bland-Altman 分析，得到肿瘤和正常肝脏组织吸收剂量体积直方图指标的结果。
使用商业软件计算的平均剂量与蒙特卡罗计算的肿瘤和正常肝组织的平均剂量相差在 3%以内。使用胸部-腹部校准计算的肿瘤平均剂量与使用 SPECT FOV 计算的平均剂量相差在 2%以内，而使用总肝轮廓、扩展总肝轮廓和收缩总肝轮廓计算的剂量分别为 SPECT FOV 计算的剂量的 68%、47%和 107%。使用胸部-腹部轮廓计算的正常肝脏组织平均剂量与使用 SPECT FOV 计算的平均剂量相差在 1.3%以内，而使用总肝轮廓、扩展总肝轮廓和收缩总肝轮廓计算的剂量分别为 SPECT FOV 计算的剂量的 73%、50%和 114%。
商业软件的平均误差<3%可被认为是 Y-SIRT 剂量测定的临床可接受值。使用胸部-腹部轮廓的 Y-SPECT 自我校准进行吸收剂量量化与使用 SPECT FOV 计算的结果相当，但使用总肝轮廓进行自我校准会产生高得多（约 70%）的剂量值。我们的研究揭示了较大的偏差，这表明在比较不同临床研究中的 Y-SIRT 剂量测定时，必须采用一致的吸收剂量计算方法。
