Tapp Katie N, Lea William B, Johnson Matthew S, Tann Mark, Fletcher James W, Hutchins Gary D
Department of Radiology and Imaging Science, Indiana University School of Medicine, Indianapolis, Indiana; and School of Health Sciences, Purdue University, West Lafayette, Indiana.
Department of Radiology and Imaging Science, Indiana University School of Medicine, Indianapolis, Indiana; and.
J Nucl Med. 2014 Sep;55(9):1452-8. doi: 10.2967/jnumed.113.133629. Epub 2014 Jun 30.
PET/CT imaging after radioembolization is a viable method for determining the posttreatment (90)Y distribution in the liver. Low true-to-random coincidence ratios in (90)Y PET studies limit the quantitative accuracy of these studies when reconstruction algorithms optimized for traditional PET imaging are used. This study examined these quantitative limitations and assessed the feasibility of generating radiation dosimetry maps in liver regions with high and low (90)Y concentrations.
(90)Y PET images were collected on a PET/CT scanner and iteratively reconstructed with the vendor-supplied reconstruction algorithm. PET studies on a Jaszczak cylindric phantom were performed to determine quantitative accuracy and minimum detectable concentration (MDC). (90)Y and (18)F point-source studies were used to investigate the possible increase in detected random coincidence events due to bremsstrahlung photons. Retrospective quantitative analyses were performed on (90)Y PET/CT images obtained after 65 right or left hepatic artery radioembolizations in 59 patients. Quantitative image errors were determined by comparing the measured image activity with the assayed (90)Y activity. PET images were converted to dose maps through convolution with voxel S values generated using MCNPX, a Monte Carlo N-particle transport code system for multiparticle and high-energy applications. Tumor and parenchyma doses and potential bias based on measurements found below the MDC were recorded.
Random coincidences were found to increase in (90)Y acquisitions, compared with (18)F acquisitions, at similar positron emission rates because of bremsstrahlung photons. Positive bias was observed in all images. Quantitative accuracy was achieved for phantom inserts above the MDC of 1 MBq/mL. The mean dose to viable tumors was 183.6 ± 156.5 Gy, with an average potential bias of 3.3 ± 6.4 Gy. The mean dose to the parenchyma was 97.1 ± 22.1 Gy, with an average potential bias of 8.9 ± 4.9 Gy.
The low signal-to-noise ratio caused by low positron emission rates and high bremsstrahlung photon production resulted in a positive bias on (90)Y PET images reconstructed with conventional iterative algorithms. However, quantitative accuracy was good at high activity concentrations, such as those found in tumor volumes, allowing for adequate tumor (90)Y PET/CT dosimetry after radioembolization.
放射性栓塞术后的PET/CT成像对于确定肝脏中治疗后（90）Y的分布是一种可行的方法。当使用针对传统PET成像优化的重建算法时，（90）Y PET研究中较低的真符合与随机符合比限制了这些研究的定量准确性。本研究检查了这些定量限制，并评估了在（90）Y浓度高和低的肝脏区域生成辐射剂量图的可行性。
在PET/CT扫描仪上采集（90）Y PET图像，并使用供应商提供的重建算法进行迭代重建。对Jaszczak圆柱形体模进行PET研究，以确定定量准确性和最小可检测浓度（MDC）。使用（90）Y和（18）F点源研究来调查由于轫致辐射光子导致的检测到的随机符合事件可能增加的情况。对59例患者在右或左肝动脉放射性栓塞65次后获得的（90）Y PET/CT图像进行回顾性定量分析。通过将测量的图像活性与测定的（90）Y活性进行比较来确定定量图像误差。通过与使用MCNPX（一种用于多粒子和高能应用的蒙特卡罗N粒子输运代码系统）生成的体素S值进行卷积，将PET图像转换为剂量图。记录肿瘤和实质剂量以及基于低于MDC的测量值的潜在偏差。
由于轫致辐射光子，在相似的正电子发射率下，与（18）F采集相比，（90）Y采集中发现随机符合增加。在所有图像中均观察到正偏差。对于MDC高于1 MBq/mL的体模插入物，实现了定量准确性。存活肿瘤的平均剂量为183.6±156.5 Gy，平均潜在偏差为3.3±6.4 Gy。实质的平均剂量为97.1±22.1 Gy，平均潜在偏差为8.9±4.9 Gy。
由低正电子发射率和高轫致辐射光子产生导致的低信噪比，在用传统迭代算法重建的（90）Y PET图像上产生了正偏差。然而，在高活性浓度下，如在肿瘤体积中发现的浓度，定量准确性良好，允许在放射性栓塞术后进行充分的肿瘤（90）Y PET/CT剂量测定。
