Sgouros G
Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
Med Phys. 1998 Aug;25(8):1487-90. doi: 10.1118/1.598323.
Yttrium-90 is widely used in radioimmunotherapy but does not emit photons for imaging. Indium-111, a chemically similar atom has been used instead as a tracer for the distribution of 90Y-labeled antibodies. Recent advances in gamma camera technology have made it possible to image at energies higher than 364 keV. This work provides a theoretical analysis of the feasibility of using 87Y (485 keV, 92.2% yield) as a tracer for in vivo imaging of 90Y-labeled antibodies. Yttrium-87 may be produced by the 87Sr(p,n)87Y reaction in a cyclotron and has a 3.3 day half-life. This reaction also yields a metastable state of 87Y (87mY). Yttrium-87, itself decays to a metastable state of 87Sr (87mSr). The level of these contaminants and their anticipated impact on the utility of 87Y as a tracer for 90Y are examined theoretically. Dosimetry is performed to assess the absorbed dose associated with using 87Y. A 100 h delay following the end of bombardment of an isotopically enriched 87Sr target reduces the activity of the metastable state of 87Y in the product by 10- to 15-fold, with greater delays resulting in a further reduction. A rapid equilibration between 87Y and its daughter, 87mSr, is expected, in vivo. Although strontium is known to concentrate in bone, the electron emissions of 87mSr are short range, thereby making possible biologic effects highly position dependent; the photon emissions allow for independent imaging which may be used to perform dosimetry and thereby directly assess potential toxicity. 87Y merits further consideration as an imaging tracer for 90Y.
钇-90广泛应用于放射免疫治疗，但不发射用于成像的光子。铟-111是一种化学性质相似的原子，已被用作钇-90标记抗体分布的示踪剂。γ相机技术的最新进展使得在高于364keV的能量下成像成为可能。这项工作对使用钇-87（485keV，产率92.2%）作为钇-90标记抗体体内成像示踪剂的可行性进行了理论分析。钇-87可通过回旋加速器中的87Sr(p,n)87Y反应产生，半衰期为3.3天。该反应还会产生钇-87的亚稳态（87mY）。钇-87本身会衰变为锶-87的亚稳态（87mSr）。从理论上研究了这些污染物的水平及其对钇-87作为钇-90示踪剂效用的预期影响。进行剂量测定以评估与使用钇-87相关的吸收剂量。对同位素富集的87Sr靶进行轰击结束后延迟100小时，可使产物中钇-87亚稳态的活度降低10至15倍，延迟时间越长，活度进一步降低。预计在体内钇-87与其子体87mSr之间会迅速达到平衡。虽然已知锶会在骨骼中富集，但87mSr的电子发射射程短，因此生物效应高度依赖位置；光子发射可用于独立成像，可用于进行剂量测定，从而直接评估潜在毒性。钇-87作为钇-90的成像示踪剂值得进一步考虑。
