Mikell Justin K, Kaza Ravi K, Roberson Peter L, Younge Kelly C, Srinivasa Ravi N, Majdalany Bill S, Cuneo Kyle C, Owen Dawn, Devasia Theresa, Schipper Matthew J, Dewaraja Yuni K
Department of Radiation Oncology, University of Michigan, Ann Arbor, MI, 48109, USA.
Department of Radiology, University of Michigan Medical School, Ann Arbor, MI, USA.
EJNMMI Phys. 2018 Nov 30;5(1):31. doi: 10.1186/s40658-018-0230-y.
The purpose was to validate Y PET gradient-based tumor segmentation in phantoms and to evaluate the impact of the segmentation method on reported tumor absorbed dose (AD) and biological effective dose (BED) in Y microsphere radioembolization (RE) patients. A semi-automated gradient-based method was applied to phantoms and patient tumors on the Y PET with the initial bounding volume for gradient detection determined from a registered diagnostic CT or MR; this PET-based segmentation (PS) was compared with radiologist-defined morphologic segmentation (MS) on CT or MRI. AD and BED volume histogram metrics (D90, D70, mean) were calculated using both segmentations and concordance/correlations were investigated. Spatial concordance was assessed using Dice similarity coefficient (DSC) and mean distance to agreement (MDA). PS was repeated to assess intra-observer variability.
In phantoms, PS demonstrated high accuracy in lesion volumes (within 15%), AD metrics (within 11%), high spatial concordance relative to morphologic segmentation (DSC > 0.86 and MDA < 1.5 mm), and low intra-observer variability (DSC > 0.99, MDA < 0.2 mm, AD/BED metrics within 2%). For patients (58 lesions), spatial concordance between PS and MS was degraded compared to in-phantom (average DSC = 0.54, average MDA = 4.8 mm); the average mean tumor AD was 226 ± 153 and 197 ± 138 Gy, respectively for PS and MS. For patient AD metrics, the best Pearson correlation (r) and concordance correlation coefficient (ccc) between segmentation methods was found for mean AD (r = 0.94, ccc = 0.92), but worsened as the metric approached the minimum dose (for D90, r = 0.77, ccc = 0.69); BED metrics exhibited a similar trend. Patient PS showed low intra-observer variability (average DSC = 0.81, average MDA = 2.2 mm, average AD/BED metrics within 3.0%).
Y PET gradient-based segmentation led to accurate/robust results in phantoms, and showed high concordance with MS for reporting mean tumor AD/BED in patients. However, tumor coverage metrics such as D90 exhibited worse concordance between segmentation methods, highlighting the need to standardize segmentation methods when reporting AD/BED metrics from post-therapy Y PET. Estimated differences in reported AD/BED metrics due to segmentation method will be useful for interpreting RE dosimetry results in the literature including tumor response data.
目的是在体模中验证基于钇正电子发射断层扫描（Y PET）梯度的肿瘤分割，并评估分割方法对钇微球放射性栓塞（RE）患者报告的肿瘤吸收剂量（AD）和生物有效剂量（BED）的影响。将一种基于梯度的半自动方法应用于Y PET上的体模和患者肿瘤，梯度检测的初始边界体积由配准的诊断性计算机断层扫描（CT）或磁共振成像（MR）确定；将这种基于PET的分割（PS）与CT或MRI上放射科医生定义的形态学分割（MS）进行比较。使用两种分割方法计算AD和BED体积直方图指标（D90、D70、平均值），并研究一致性/相关性。使用骰子相似系数（DSC）和平均一致距离（MDA）评估空间一致性。重复进行PS以评估观察者内变异性。
在体模中，PS在病变体积（误差在15%以内）、AD指标（误差在11%以内）方面显示出高精度，相对于形态学分割具有较高的空间一致性（DSC＞0.86且MDA＜1.5毫米），并且观察者内变异性较低（DSC＞0.99，MDA＜0.2毫米，AD/BED指标误差在2%以内）。对于患者（58个病变），与体模相比，PS和MS之间的空间一致性有所下降（平均DSC = 0.54，平均MDA = 4.8毫米）；PS和MS的平均肿瘤AD分别为226±153和197±138戈瑞。对于患者AD指标，分割方法之间的最佳皮尔逊相关系数（r）和一致性相关系数（ccc）在平均AD方面被发现（r = 0.94，ccc = 0.92），但随着指标接近最小剂量而变差（对于D90，r = 0.77，ccc = 0.69）；BED指标呈现类似趋势。患者PS显示出较低的观察者内变异性（平均DSC = 0.81，平均MDA = 2.2毫米，平均AD/BED指标误差在3.0%以内）。
基于Y PET梯度的分割在体模中产生了准确/稳健的结果，并且在报告患者的平均肿瘤AD/BED方面与MS具有高度一致性。然而，诸如D90等肿瘤覆盖指标在分割方法之间的一致性较差，这突出表明在报告治疗后Y PET的AD/BED指标时需要标准化分割方法。由于分割方法导致的报告AD/BED指标的估计差异将有助于解释文献中的RE剂量学结果，包括肿瘤反应数据。
