Makrigiorgos G M, Adelstein S J, Kassis A I
Department of Radiology, Harvard Medical School, Shields Warren Radiation Laboratory, Boston, Massachusetts.
J Nucl Med. 1989 Nov;30(11):1856-64.
A theoretic examination of the validity at the cellular level of assumptions used in classic internal dosimetry has been undertaken. An alternate dosimetric model accounting for the consequences of selective uptake of a radiolabeled compound by specific cells in a multicellular cluster of hexagonal geometry has been developed. At the cellular level, derived dose estimates for electrons have been compared to dose estimates obtained employing the assumptions of conventional internal dosimetry. The study has been performed for all electron energies and then applied specifically to electrons emitted by 99mTc, 201Tl, 111In, and 123I. The dosimetric consequences of altering (a) the intracellular-to-extracellular radionuclide concentration, (b) the labeled cell density, and (c) the cell size have been examined for the labeled and nonlabeled cells in a cell cluster, and the conditions in which conventional dosimetry underestimates or overestimates the dose to individual cells have been indicated. It is shown that when selective intracellular uptake of a radiolabeled compound occurs in specific cells within a cell cluster, conventional dosimetry underestimates the radiation dose delivered to the labeled cells by twofold to more than 25-fold if the emitted electrons have ranges of a few micrometers or less, i.e., energies smaller than approximately 10 keV. Under the same conditions, conventional dosimetry overestimates slightly (20% to 50%) the electron radiation dose to the nonlabeled cells of the cell cluster. It is shown that inclusion of photons in the calculation of the total dose to individual cells does not alter significantly the conclusions of the present investigation.
已对经典内照射剂量学中所用假设在细胞水平的有效性进行了理论检验。已开发出一种替代剂量学模型，该模型考虑了放射性标记化合物在六边形几何形状的多细胞簇中被特定细胞选择性摄取的后果。在细胞水平上，已将推导出的电子剂量估计值与采用传统内照射剂量学假设获得的剂量估计值进行了比较。该研究针对所有电子能量进行，然后具体应用于由99mTc、201Tl、111In和123I发射的电子。已研究了改变（a）细胞内与细胞外放射性核素浓度、（b）标记细胞密度和（c）细胞大小对细胞簇中标记细胞和未标记细胞的剂量学后果，并指出了传统剂量学低估或高估单个细胞剂量的条件。结果表明，当细胞簇内特定细胞发生放射性标记化合物的选择性细胞内摄取时，如果发射的电子射程为几微米或更小，即能量小于约10keV，传统剂量学将低估传递给标记细胞的辐射剂量2倍至超过25倍。在相同条件下，传统剂量学将略微高估（20%至50%）细胞簇中未标记细胞的电子辐射剂量。结果表明，在计算单个细胞的总剂量时纳入光子不会显著改变本研究的结论。
