Hafer Kurt, Scuric Zorica, Iwamoto Keisuke S, Schiestl Robert H
Departments of Pathology, UCLA School of Medicine and Public Health, Los Angeles, California, USA.
Radiat Res. 2006 May;165(5):616-20. doi: 10.1667/RR3524.1.
Radioactive point sources are regularly used for irradiating cell culture and other biological materials. Eccentric rotation is often used to minimize dose disparities that arise from irradiating samples that span a distance from the point source. Rotation provides a great improvement in dose homogeneity compared to inert irradiation yet still presents an obvious shortcoming for exposures in which the sample completes only partial rotation or fractional rotation. In such cases, certain areas of the sample have a closer average distance to the radiation source than other areas within the same sample. This obstacle can be partially overcome by adjusting rotation speed so the sample traverses a full rotation (or multiple thereof) throughout the total irradiation time. Here we investigate the effects of irradiation with eccentric rotation on dose homogeneity. We show that due to the inverse square law that governs dose, even exposures with full rotation result in inhomogeneous dose distributions. This dose inhomogeneity can be substantial, especially for large samples and small source- sample distances. We observed a 33% difference in survival across 100-mm dishes and a 400% difference for 150-mm dishes. The dose inhomogeneity inherent to eccentric rotation increases the actual average dose delivered across the sample compared to that delivered at sample center. We offer a table of correction factors that account for this dose increase and correct the dose delivered at center to the actual average dose delivered across the entire sample.
放射性点源常用于辐照细胞培养物及其他生物材料。偏心旋转常用于使因辐照跨越距点源一定距离的样品而产生的剂量差异最小化。与固定辐照相比，旋转在剂量均匀性方面有很大改善，但对于样品仅完成部分旋转或分数旋转的照射情况，仍存在明显缺点。在这种情况下，样品的某些区域与辐射源的平均距离比同一样品内的其他区域更近。通过调整旋转速度，使样品在整个辐照时间内完成一整圈（或多圈）旋转，可部分克服这一障碍。在此，我们研究偏心旋转辐照对剂量均匀性的影响。我们表明，由于剂量遵循平方反比定律，即使是整圈旋转的照射也会导致剂量分布不均匀。这种剂量不均匀性可能很大，尤其是对于大样品和小源 - 样品距离的情况。我们观察到，在直径100毫米的培养皿中，存活率相差33%，在直径150毫米的培养皿中相差400%。与在样品中心给予的剂量相比，偏心旋转固有的剂量不均匀性会增加样品所接受的实际平均剂量。我们提供了一个校正因子表，用于考虑这种剂量增加，并将在中心给予的剂量校正为整个样品所接受的实际平均剂量。
