Uusijärvi Helena, Bernhardt Peter, Ericsson Thomas, Forssell-Aronsson Eva
Department of Radiation Physics, Göteborg University, Sahlgrenska University Hospital, SE-413 45 Göteborg, Sweden.
Med Phys. 2006 Sep;33(9):3260-9. doi: 10.1118/1.2229428.
Various radionuclides have been proposed for systemic tumor therapy. However, in most dosimetric analysis of proposed radionuclides the charged particles are taken into consideration while the potential photons are ignored. The photons will cause undesirable irradiation of normal tissue, and increase the probability of toxicity in, e.g., the bone marrow. The aim of this study was to investigate the dosimetric properties according to particle range, photon emission, and subcellular radionuclide distribution, of a selection of radionuclides used or proposed for radionuclide therapy, and to investigate the possibility of dividing radionuclides into groups according to their dosimetric properties. The absorbed dose rate to the tumors divided by the absorbed dose rate to the normal tissue (TND) was estimated for different tumor sizes in a mathematical model of the human body. The body was simulated as a 70-kg ellipsoid and the tumors as spheres of different sizes (1 ng-100 g). The radionuclides were either assumed to be uniformly distributed throughout the entire tumor and normal tissue, or located in the nucleus or the cytoplasm of the tumor cells and on the cell membrane of the normal cells. Fifty-nine radionuclides were studied together with monoenergetic electrons, positrons, and alpha particles. The tumor and normal tissue were assumed to be of water density. The activity concentration ratio between the tumor and normal tissue was assumed to be 25. The radionuclides emitting low-energy electrons combined with a low photon contribution, and the alpha emitters showed high TND values for most tumor sizes. Electrons with higher energy gave reduced TND values for small tumors, while a higher photon contribution reduced the TND values for large tumors. Radionuclides with high photon contributions showed low TND value for all tumor sizes studied. The radionuclides studied could be divided into four main groups according to their TND values: beta emitters, Auger electron emitters, photon emitters, and alpha emitters. The TND values of the beta emitters were not affected by the subcellular distribution of the radionuclide. The TND values of the Auger electron emitters were affected by the subcellular radionuclide distribution. The photon emitters showed low TND values that were only slightly affected by the subcellular radionuclide distribution. The alpha emitters showed high TND values that were only slightly affected by the subcellular radionuclide distribution. This dosimetric characterization of radionuclides may be valuable in choosing the appropriate radionuclides for specific therapeutic applications.
已有多种放射性核素被提议用于全身肿瘤治疗。然而，在对提议的放射性核素进行的大多数剂量分析中，仅考虑了带电粒子，而忽略了潜在的光子。光子会对正常组织造成不良照射，并增加例如骨髓中毒性发生的概率。本研究的目的是根据粒子射程、光子发射以及亚细胞放射性核素分布，研究用于或提议用于放射性核素治疗的一系列放射性核素的剂量学特性，并研究根据其剂量学特性将放射性核素分组的可能性。在人体数学模型中，针对不同大小的肿瘤估算肿瘤吸收剂量率与正常组织吸收剂量率之比（TND）。人体模拟为一个70千克的椭球体，肿瘤模拟为不同大小（1纳克至100克）的球体。放射性核素要么假定在整个肿瘤和正常组织中均匀分布，要么位于肿瘤细胞的细胞核或细胞质以及正常细胞的细胞膜上。研究了59种放射性核素以及单能电子、正电子和α粒子。假定肿瘤和正常组织的密度与水相同。假定肿瘤与正常组织的活度浓度比为25。发射低能电子且光子贡献较低的放射性核素，以及α发射体在大多数肿瘤大小情况下均显示出较高的TND值。能量较高的电子对于小肿瘤会使TND值降低，而光子贡献较高则会使大肿瘤的TND值降低。光子贡献较高的放射性核素在所有研究的肿瘤大小情况下均显示出较低的TND值。根据TND值，所研究的放射性核素可分为四个主要组：β发射体、俄歇电子发射体、光子发射体和α发射体。β发射体的TND值不受放射性核素亚细胞分布的影响。俄歇电子发射体的TND值受亚细胞放射性核素分布的影响。光子发射体显示出较低的TND值，仅受亚细胞放射性核素分布的轻微影响。α发射体显示出较高的TND值，仅受亚细胞放射性核素分布的轻微影响。放射性核素的这种剂量学特征对于为特定治疗应用选择合适的放射性核素可能具有重要价值。
