Radiation dose estimate in small animal SPECT and PET
Radiation dose estimate in small animal SPECT and PET
复制标题
DOI：
10.1118/1.1781553
复制
发表时间：
2004-09-01
期刊：
影响因子：
3.8
通讯作者：
Hasegawa, BH
中科院分区：
文献类型：
--
作者：
Funk, T;Sun, MS;Hasegawa, BH
辐射剂量的计算对于评估SPECT和PET等医学成像技术中电离辐射的医学和生物学影响非常重要。相比之下，小动物SPECT和PET成像的辐射剂量估计不是很好地建立。因此，我们估算了小动物成像常用的同位素（如18 F、Tc-99 m、Tl-201、In-111、I-123和I-125）对小鼠和大鼠的全身辐射剂量。我们近似小鼠和大鼠的身体均匀的软组织等效椭球体。小鼠和大鼠大小的椭圆体的质量分别为30 g和300 g，主轴比为1：1：4和0.7：1：4。利用蒙特卡罗软件包MCNP计算了不同光子能量的吸收分数。使用这些值，然后我们计算了两种几何形状的MIRD S值，这两种几何形状模拟了动物体内的活性分布：（a）中心点源和（B）均匀分布源，并将这些值与MIRD手册8中列出的小椭球体的S值计算进行了比较，以验证我们的结果。最后，我们计算了辐射剂量，考虑到放射性药物的生物半衰期和活动的管理量。我们的计算产生的S值对于SPECT试剂在1.06 X 10（-13）戈伊/Bq s和2.77 X 10（-13）戈伊/Bq s之间，对于PET试剂18 F在15.0 X 10（-13）戈伊/Bq s之间，假设具有均匀源分布的小鼠大小的椭圆体。椭球体中中心点源的S值比均匀源分布的S值高约10%。此外，小鼠大小的椭圆体的S值比大鼠大小的椭圆体高约10倍，反映了质量差异。我们回顾了已发表的数据，以获得小动物成像的给药放射性和停留时间。根据这些值和我们计算的S值，我们估计小动物的全身剂量范围为小鼠6 cGy至90 cGy，大鼠约1 cGy至27 cGy。与小鼠的致死剂量（LD 50/30约为7戈伊）相比，小动物成像中的全身剂量可能非常高。因此，应仔细监测小动物成像中的剂量，并将给药活性保持在最低水平。这些结果也强调了进一步开发仪器的必要性，以提高检测效率并减少小动物成像中的辐射剂量。(C)2004年美国医学物理学家协会。
Calculations of radiation dose are important in assessing the medical and biological implications of ionizing radiation in medical imaging techniques such as SPECT and PET. In contrast, radiation dose estimates of SPECT and PET imaging of small animals are not very well established. For that reason we have estimated the whole-body radiation dose to mice and rats for isotopes such as 18F, Tc-99m, Tl-201, In-111, I-123, and I-125 that are used commonly for small animal imaging. We have approximated mouse and rat bodies with uniform soft tissue equivalent ellipsoids. The mouse and rat sized ellipsoids had a mass of 30 g and 300 g, respectively, and a ratio of the principal axes of 1: 1:4 and 0.7:1:4. The absorbed fractions for various photon energies have been calculated using the Monte Carlo software package MCNP. Using these values, we then calculated MIRD S-values for two geometries that model the distribution of activity in the animal body: (a) a central point source and (b) a homogeneously distributed source, and compared these values against S-value calculations for small ellipsoids tabulated in MIRD Pamphlet 8 to validate our results. Finally we calculated the radiation dose taking into account the biological half-life of the radiopharmaceuticals and the amount of activity administered. Our calculations produced S-values between 1.06 X 10(-13) Gy/Bq s and 2.77 X 10(-13) Gy/Bqs for SPECT agents, and 15.0X 10(-13) Gy/Bq s for the PET agent 18F, assuming mouse sized ellipsoids with uniform source distribution. The S-values for a central point source in an ellipsoid are about 10% higher than the values obtained for the uniform source distribution. Furthermore, the S-values for mouse sized ellipsoids are approximately 10 times higher than for the rat sized ellipsoids reflecting the difference in mass. We reviewed published data to obtain administered radioactivity and residence times for small animal imaging. From these values and our computed S-values we estimated that the whole body dose in small animals ranges between 6 cGy and 90 cGy for mice and between about 1 cGy and 27 cGy for rats. The whole body dose in small animal imaging can be very high in comparison to the lethal dose to mice (LD50/30approximate to7 Gy). For this reason the dose in small animal imaging should be monitored carefully and the administered activity should be kept to a minimum. These results also underscore the need of further development of instrumentation that improves detection efficiency and reduces radiation dose in small animal imaging. (C) 2004 American Association of Physicists in Medicine.