Hoshi M, Goodhead D T, Brenner D J, Bance D A, Chmielewski J J, Paciotti M A, Bradbury J N
Phys Med Biol. 1985 Oct;30(10):1029-41. doi: 10.1088/0031-9155/30/10/002.
Ultrasoft x-rays of 0.3-5 keV have provided a unique tool for the investigation of intracellular mechanisms of radiation action in biological organisms, including mammalian cells. However, their use presents unique practical problems in dosimetry and experimental design. Detailed interpretation of the biological results requires reliable dosimetry and well characterised monoenergetic beams. This paper presents a comparison between two fundamentally different dosimetric techniques, namely the ionisation current in an extrapolation chamber and photon counts in a proportional counter. Agreement within 7% was obtained when these two methods were applied to an Al K x-ray beam (1.5 keV) from an MRC cold-cathode transmission target discharge tube as previously used in many biological experiments. Photographic film was calibrated as a relative dosimetric technique and used for investigation of the intensity uniformity of the radiation field. These techniques provide a comprehensive characterisation of the beam in the position of the biological cells, including photon flux (or absorbed dose rate), spectral purity (showing much less than 1% bremsstrahlung relative to characteristic Al x-rays) and uniformity over the irradiation area (within about 5% for mammalian cell irradiations).
能量在0.3至5千电子伏特之间的极软X射线为研究包括哺乳动物细胞在内的生物机体中辐射作用的细胞内机制提供了一种独特的工具。然而，其应用在剂量测定和实验设计方面存在独特的实际问题。对生物学结果的详细解读需要可靠的剂量测定以及特征明确的单能束流。本文对两种根本不同的剂量测定技术进行了比较，即外推电离室中的电离电流和正比计数器中的光子计数。当将这两种方法应用于来自医学研究委员会（MRC）冷阴极透射靶放电管的铝K X射线束（1.5千电子伏特）时，此前该束流已用于许多生物学实验，二者的结果一致性在7%以内。将摄影胶片校准为一种相对剂量测定技术，并用于研究辐射场的强度均匀性。这些技术全面表征了位于生物细胞位置处的束流，包括光子通量（或吸收剂量率）、光谱纯度（相对于特征性铝X射线，韧致辐射显示远低于1%）以及照射区域内的均匀性（对于哺乳动物细胞照射而言，在约5%以内）。
