Thomas M Allan, Laforest Richard, Karageorgiou John, Giardina Dan, Fraum Tyler J, Malone Chris D, Mikell Justin K
Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO, 63130, USA.
Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, 63130, USA.
EJNMMI Phys. 2024 Dec 18;11(1):104. doi: 10.1186/s40658-024-00705-4.
Prior studies have established that macroaggregated albumin (MAA)-SPECT/CT offers more robust lung shunt fraction (LSF) and lung mean absorbed dose (LMD) estimates in Y radioembolization in comparison to planar imaging. However, incomplete SPECT/CT coverage of the lungs is common due to clinical workflows, complicating its potential use for LSF and LMD calculations. In this work, lung truncation in MAA-SPECT/CT was addressed via correction strategies to improve Y treatment planning.
Lung truncation was simulated in 56 cases with adequate (> 90%, mean: 98%) lung coverage in MAA-SPECT/CT by removing slices in ~ 5 mm increments from the lung apices to the diaphragm. A wide range of lung coverages from 100% to < 1% in ~ 2% increments were created. LSF and LMD were calculated with four methods. (1) 2D planar imaging standard (not truncated), truncated lung SPECT/CT data was: (2) used with no corrections (SPECT), (3) uniformly extrapolated to full lung coverage (SPECT), (4) fit with an empirical model to predict lung counts at full lung coverage (SPECT). To determine counts for LSF, full lung volumes, those modified at the lung/liver boundary (Lungs 2-cm), and those isolated to the left lung (Left Lung) were used. The correction methods were then applied to 31 independent cases without full lung coverage (< 90%, mean: 74%). The variations in LSF and LMD estimates from each correction method were analyzed.
Averaged across simulated lung coverages from 40 to 80%, percent errors relative to non-truncated data for SPECT were (mean ± σ) - 22% ± 15% for LSF and 34% ± 29% for LMD. SPECT had similar errors with 29% ± 26% for both LSF and LMD. SPECT yielded the most accurate and precise estimates for LSF and LMD, with errors of 11% ± 20% for both. The Left Lung approach equalized LMD errors in all three correction methods, with percent errors of 3% ± 17% (SPECT), 2% ± 17% (SPECT), and 4% ± 13% (SPECT). In the 31 cases without ground truth LSF or LMD, Left Lung produced highly comparable LMD estimates, with a mean (max) coefficient of variation across the three correction methods of 4% (20%).
LSF and LMD can be estimated for Y radioembolization using truncated lung coverage data in MAA-SPECT/CT. Empirical models to predict lung counts at full lung coverage produced LSF and LMD estimates with minimal bias and uncertainty. With lung/liver boundary adjustments, all SPECT/CT methods assessed in this work yielded LMD estimates comparable to ground truth, even down to 50% lung coverage.
先前的研究已经证实，与平面成像相比，在钇[90Y]放射性栓塞治疗中，大颗粒聚合白蛋白（MAA）-SPECT/CT能提供更可靠的肺分流分数（LSF）和肺平均吸收剂量（LMD）估计值。然而，由于临床工作流程的原因，肺部SPECT/CT覆盖不完整的情况很常见，这使得其在LSF和LMD计算中的潜在应用变得复杂。在这项研究中，通过校正策略解决了MAA-SPECT/CT中的肺部截断问题，以改善钇[90Y]治疗计划。
在56例MAA-SPECT/CT肺部覆盖率足够（>90%，平均：98%）的病例中模拟肺部截断，从肺尖到膈肌以约5毫米的增量去除切片。创建了从100%到<1%、以约2%的增量变化的广泛肺部覆盖率范围。用四种方法计算LSF和LMD。（1）二维平面成像标准（未截断），截断的肺部SPECT/CT数据为：（2）不进行校正使用（SPECT），（3）均匀外推至全肺覆盖（SPECT），（4）用经验模型拟合以预测全肺覆盖时的肺部计数（SPECT）。为确定LSF的计数，使用了全肺体积、在肺/肝边界处修改的体积（肺2厘米）以及分离出的左肺体积（左肺）。然后将校正方法应用于31例肺部未完全覆盖（<90%，平均：74%）的独立病例。分析了每种校正方法对LSF和LMD估计值的差异。
在40%至80%的模拟肺部覆盖率范围内平均计算，相对于未截断数据，SPECT的LSF百分比误差为（均值±标准差）-22%±15%，LMD为34%±29%。SPECT的误差与之相似，LSF和LMD均为29%±26%。SPECT对LSF和LMD的估计最为准确和精确，误差均为11%±20%。左肺方法在所有三种校正方法中使LMD误差均等，百分比误差分别为3%±17%（SPECT）、2%±17%（SPECT）和4%±13%（SPECT）。在31例无真实LSF或LMD的病例中，左肺产生的LMD估计值具有高度可比性，三种校正方法的平均（最大）变异系数为4%（20%）。
使用MAA-SPECT/CT中截断的肺部覆盖数据可以估计钇[90Y]放射性栓塞治疗的LSF和LMD。预测全肺覆盖时肺部计数的经验模型产生的LSF和LMD估计值偏差和不确定性最小。通过肺/肝边界调整，本研究中评估的所有SPECT/CT方法产生的LMD估计值与真实值相当，即使肺部覆盖率低至50%。
