Duggan L, Warren-Forward H, Smith T, Kron T
Newcastle Mater Misericordiae Hospital, Department of Radiation Oncology, Waratah NSW 2298, Australia.
Br J Radiol. 2003 Apr;76(904):232-7. doi: 10.1259/bjr/79291075.
Many departments still do not use recommended radiographic parameters to X-ray neonates. Direct, accurate dose measurements of individual examinations may assist a department in justifying technique modifications that provide a substantial dose reduction without a significant loss of image quality. The aim of this study was to investigate dose reduction techniques for neonates in the intensive care unit. Alterations in beam energy (kVp and filtration) and collimation were investigated using specially designed phantoms mimicking a 700 g and 2000 g neonate, and ultrasensitive LiF:Mg,Cu,P thermoluminescence dosimeters (TLDs). Differences in entrance surface dose (ESD) and dose at depth (3 cm or 5 cm) were compared for two, overlapping fields centred individually on the chest and abdomen (Technique 1) and one large chest-abdomen field (Technique 2 or babygram). The large phantom was irradiated at 54 kVp, 60 kVp and 70 kVp without additional filtration and at 66 kVp and 70 kVp with a rare-earth hafnium filter. Focus-film distance (FFD) and mAs were adjusted to maintain optical density (OD) on each radiograph. The baseline dose at 54 kVp and 100 cm FFD was (46+/-2) micro Gy. Increasing the tube potential from 54 kVp to 70 kVp without additional filtration reduced the ESD by 27%. However, the addition of a 0.05 mm hafnium filter at 66 kVp further reduced the radiation dose by 13%, to produce an ESD of (28+/-2) micro Gy. All contrast details were observable at 66 kVp with hafnium filtration. Technique 1 may lead to an increase in effective dose due to field overlap, which diverges at depth, and increased scatter at the periphery of the fields.
许多科室仍未采用推荐的X射线新生儿造影参数。对单项检查进行直接、准确的剂量测量，可能有助于科室证明技术改进的合理性，这些改进能在不显著降低图像质量的情况下大幅降低剂量。本研究的目的是调查重症监护病房新生儿的剂量降低技术。使用专门设计的模拟700克和2000克新生儿的体模以及超灵敏的氟化锂镁铜磷热释光剂量计（TLD），研究了射线能量（千伏峰值和过滤）及准直的变化。比较了分别以胸部和腹部为中心的两个重叠区域（技术1）和一个大的胸腹区域（技术2或婴儿胸片）在体表入射剂量（ESD）和深度（3厘米或5厘米）处剂量的差异。大的体模在54千伏峰值、60千伏峰值和70千伏峰值下无额外过滤进行照射，以及在66千伏峰值和70千伏峰值下使用稀土铪滤过进行照射。调整焦点-胶片距离（FFD）和毫安秒（mAs）以保持每张X光片的光学密度（OD）。在54千伏峰值和100厘米FFD时的基线剂量为（46±2）微戈瑞。在无额外过滤的情况下，将管电压从54千伏峰值增加到70千伏峰值可使ESD降低27%。然而，在66千伏峰值时添加0.05毫米铪滤过可使辐射剂量进一步降低13%，产生的ESD为（28±2）微戈瑞。在66千伏峰值并使用铪滤过时，所有对比度细节均可观察到。技术1可能会因野重叠导致有效剂量增加，野重叠在深度处发散，并在野的周边增加散射。
