Oehme Liane, Bartzsch Thomas, Maucksch Ute, Freudenberg Robert, Wunderlich Gerd, Kotzerke Jörg
Nuklearmedizin. 2018 Jun;57(3):108-116. doi: 10.3413/Nukmed-0954-17-12. Epub 2018 Jun 5.
Combined internal-external radiotherapy (CIERT) requires a unified assessment of biologic radiation effects in addition to the total dose. The concept of biological effective dose (BED) was evaluated in a cell model.
The thyroid NIS-positive cell line FRTL-5 was irradiated with X-ray and the radiotracer Tc-99m pertechnetate either alone or in combination. The cellular uptake of the radionuclide during the incubation time of 24 h was controlled by the presence or absence of perchlorate. Dose calculation was performed based on measured uptake values. Cell specific radiobiologic parameters were derived from dose effect curves using the colony forming assay as biological endpoint. For the combination of the radiation qualities the sequence and time difference were varied. Cell survival was compared with the prediction of the BED model.
The radiobiologic parameters from X-ray dose response were α = (0.22 ± 0.02) Gy and β = (0.021 ± 0.001) Gy. The half life for repair was (1.51 ± 0.21) h. These values could also explain the dose response curves for Tc-99m-irradiation with exponential decreasing dose rate. CIERT experiments showed no significant differences in cell survival regarding sequence and irradiation break. When the radionuclide uptake was not prevented the cell survival for the combination of X-ray and Tc-99m was lower than the prediction by BED calculations.
The validity of the BED formalism for different dose rates and radiation qualities was verified. Supraaddive effects measured in the combination of X-ray and intracellular Tc-99m might be caused by Auger and conversion electrons, however further experiments are necessary.
内外联合放射治疗（CIERT）除了需要对总剂量进行评估外，还需要对生物辐射效应进行统一评估。本研究在细胞模型中评估了生物有效剂量（BED）的概念。
用X射线和放射性示踪剂锝-99m高锝酸盐单独或联合照射甲状腺NIS阳性细胞系FRTL-5。在24小时的孵育时间内，通过有无高氯酸盐来控制放射性核素的细胞摄取。基于测量的摄取值进行剂量计算。使用集落形成试验作为生物学终点，从剂量效应曲线中得出细胞特异性放射生物学参数。对于不同辐射性质的联合，改变照射顺序和时间间隔。将细胞存活率与BED模型的预测结果进行比较。
X射线剂量反应的放射生物学参数为α =（0.22±0.02）Gy，β =（0.021±0.001）Gy。修复半衰期为（1.51±0.21）小时。这些值也可以解释锝-99m照射剂量率呈指数下降的剂量反应曲线。CIERT实验表明，在照射顺序和照射间隔方面，细胞存活率没有显著差异。当不阻止放射性核素摄取时，X射线和锝-99m联合照射后的细胞存活率低于BED计算的预测值。
验证了BED形式主义对于不同剂量率和辐射性质的有效性。X射线与细胞内锝-99m联合照射时测得的超相加效应可能是由俄歇电子和转换电子引起的，然而还需要进一步的实验。
