Monte Carlo evaluation of object shape effects in iodine-1 31 SPET tumor activity quantification
Monte Carlo evaluation of object shape effects in iodine-1 31 SPET tumor activity quantification
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DOI：
10.1007/s002590100551
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发表时间：
2001-07-01
期刊：
影响因子：
--
通讯作者：
Koral, KF
中科院分区：
文献类型：
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作者：
Dewaraja, YK;Ljungberg, M;Koral, KF
在我们的临床碘-131单光子发射断层扫描（SPET）定量放射免疫治疗，校准和部分体积校正的基础上的测量与phantomy包含球模拟患者的肿瘤，即使真实的肿瘤往往是非球形的。在这项研究中，蒙特卡罗模拟被用来评估对象的形状如何影响“溢出”和“溢出”，这是与I-131 SPET的空间分辨率差的量化误差的主要来源。模拟形状不同（球体、圆柱体和不规则结构）但活动和体积相同的物体。迭代重建采用衰减和三能量窗散射补偿。在重建图像中使用物理边界和使用扩展边界来定义VOI，以允许有限的分辨率。当使用物理边界时，溢出和溢出对于非球形结构比对于球形结构更显著。在对象体积的范围内（50-200毫升），并在所有的背景水平，在圆柱体中的VOI计数低于VOI计数的领域。这种低估随着物体尺寸的减小而增加（对于冷背景，在200 ml时为-18%，50 ml时为-39%）。它也随着背景活动的增加而减少，因为溢出部分地补偿了溢出。结果表明，当VOI大于物体的物理尺寸时，只有在冷背景的情况下，结果才与物体的形状和尺寸无关。使用与我们诊所中使用的程序类似的程序进行活性定量。通过简单的基于球体的部分体积校正改善了非球形物体的量化，但在某些情况下误差仍然很大（例如，对于冷背景中的50 ml圆柱体，误差为-39%;对于基于非霍奇金淋巴瘤患者的X射线计算机断层扫描上勾画的典型肿瘤定义的200 ml不规则结构，误差为-35%）。通过患者特异性Monte Carlo模拟进行部分容积校正可提供更好的定量准确性。
In our clinical iodine-131 single-photon emission tomography (SPET) quantification for radioimmunotherapy, calibration and partial volume correction are based on measurements with phantoms containing spheres to simulate patient tumors even though real tumors are frequently nonspherical. In this study, Monte Carlo simulation was used to evaluate how object shape influences "spill-out" and "spill-in", which are major sources of quantification error associated with the poor spatial resolution of I-131 SPET. Objects that varied in shape (spheres, cylinders, and an irregular structure) but were identical in activity and volume were simulated. Iterative reconstruction employed both attenuation and triple-energy-window scatter compensation. VOIs were defined in the reconstructed images both using physical boundaries and using expanded boundaries to allow for the limited resolution. When physical boundaries were used, both spill-out and spill-in were more significant for nonspherical structures than for spherical structures. Over the range of object volumes (50-200 ml) and at all background levels, VOI counts in cylinders were lower than VOI counts in spheres. This underestimation increased with decrease in object size (for the cold background -18% at 200 ml and -39% at 50 ml). It also decreased with increase in background activity because spill-in partially compensated for spill-out. It was shown that with a VOI larger than physical size, the results are independent of object shape and size only in the case of cold background. Activity quantification was carried out using a procedure similar to that used in our clinic. Quantification of nonspherical objects was improved by simple sphere-based partial volume correction, but the error was still large in some cases (for example, -39% for a 50-ml cylinder in a cold background and -35% for a 200-ml irregular structure defined on the basis of a typical tumor outlined on an X-ray computed tomography scan of a patient with non-Hodgkin's lymphoma). Partial volume correction by patient-specific Monte Carlo simulation may provide better quantification accuracy.