Jentzen W, Freudenberg L, Bockisch A
Department of Nuclear Medicine, University of Duisburg-Essen, Essen, Germany.
Q J Nucl Med Mol Imaging. 2011 Feb;55(1):21-43.
Iodine-131-labelled agents are successfully used in cancer treatment. In the pretherapy dosimetry approach, positron emission tomography/computed tomography (PET/CT) using (124)I provides a modality to estimate absorbed dose to tumours and can be considered as the preferred imaging method for this purpose in (131)I radiopharmaceutical therapies. For accurate dosimetry, serial measurements of activity concentrations (ACs) over an appropriate time period are necessary. Consequently, accurate AC determination is of paramount importance in PET/CT-based lesion dosimetry using (124)I-labelled agents. After presenting an historical overview of (124)I clinical application, this review focuses on factors impairing PET image quantification accuracy and on methods of correcting for these effects. Specifically, the emission of prompt gamma photons in the (124)I decay process that are detected in coincidence with each other and with the annihilation photon, and the low (124)I positron branching ration of only 23% raise concerns regarding image quantification accuracy. This review discusses this prompt gamma effect, its impact and approaches to correct for this phenomenon. In (124)I lesion dosimetry, recovery coefficients (RCs) are commonly used to compensate primarily for partial-volume effect but also, in a simplistic way, for prompt gamma coincidence effect; the main methodological factors affecting the RC-corrected (124)I AC are described. Finally, special issues in image (124)I quantification are reviewed, including coadministration of high therapeutic activities of 131I, shine-through artefact, and transmission-contamination effect occurring in stand-alone PET systems.
碘 - 131标记的制剂已成功应用于癌症治疗。在前治疗剂量测定方法中，使用（124）I的正电子发射断层扫描/计算机断层扫描（PET/CT）提供了一种估计肿瘤吸收剂量的方法，并且在（131）I放射性药物治疗中可被视为用于此目的的首选成像方法。为了进行准确的剂量测定，在适当的时间段内对活度浓度（AC）进行连续测量是必要的。因此，在使用（124）I标记制剂的基于PET/CT病变剂量测定中，准确测定AC至关重要。在介绍了（124）I临床应用的历史概况后，本综述重点关注影响PET图像定量准确性的因素以及校正这些影响的方法。具体而言，（124）I衰变过程中产生的瞬发伽马光子与湮灭光子相互符合探测到，以及仅23%的低（124）I正电子分支比引发了对图像定量准确性的担忧。本综述讨论了这种瞬发伽马效应、其影响以及校正该现象的方法。在（124）I病变剂量测定中，恢复系数（RC）通常主要用于补偿部分容积效应，但也以一种简单的方式用于补偿瞬发伽马符合效应；描述了影响经RC校正的（124）I AC的主要方法学因素。最后，综述了图像（124）I定量中的特殊问题，包括高治疗活度的131I的共同给药、穿透伪影以及独立PET系统中发生的传输污染效应。
