Midgley Stewart, Schleich Nanette, Merchant Alex, Stevenson Andrew
South Australian Medical Imaging, Australia.
Department of Radiation Therapy, University of Otago, Wellington, New Zealand.
J Synchrotron Radiat. 2019 Mar 1;26(Pt 2):517-527. doi: 10.1107/S1600577518018015. Epub 2019 Feb 15.
The dose length product (DLP) method for medical computed tomography (CT) dosimetry is applied on the Australian Synchrotron Imaging and Medical Beamline (IMBL). Beam quality is assessed from copper transmission measurements using image receptors, finding near 100% (20 keV), 3.3% (25 keV) and 0.5% (30-40 keV) relative contributions from third-harmonic radiation. The flat-panel-array medical image receptor is found to have a non-linear dose response curve. The amount of radiation delivered during an axial CT scan is measured as the dose in air alone, and inside cylindrical PMMA phantoms with diameters 35-160 mm for mono-energetic radiation 25-100 keV. The radiation output rate for the IMBL is comparable with that used for medical CT. Results are presented as the ratios of CT dose indices (CTDI) inside phantoms to in air with no phantom. Ratios are compared for the IMBL against medical CT where bow-tie filters shape the beam profile to reduce the absorbed dose to surface organs. CTDI ratios scale measurements in air to estimate the volumetric CTDI representing the average dose per unit length, and the dose length product representing the absorbed dose to the scanned volume. Medical CT dose calculators use the DLP, beam quality, axial collimation and helical pitch to estimate organ doses and the effective dose. The effective dose per unit DLP for medical CT is presented as a function of body region, beam energy and sample sizes from neonate to adult.
医学计算机断层扫描（CT）剂量测定的剂量长度乘积（DLP）方法应用于澳大利亚同步加速器成像与医学光束线（IMBL）。通过使用图像受体进行铜透射测量来评估光束质量，发现三次谐波辐射的相对贡献接近100%（20 keV）、3.3%（25 keV）和0.5%（30 - 40 keV）。发现平板阵列医学图像受体具有非线性剂量响应曲线。轴向CT扫描期间传递的辐射量仅作为空气中的剂量以及在直径为35 - 160 mm的圆柱形聚甲基丙烯酸甲酯（PMMA）体模内对于25 - 100 keV单能辐射的剂量进行测量。IMBL的辐射输出率与医学CT所使用的相当。结果以体模内CT剂量指数（CTDI）与无体模时空气中CTDI的比值形式呈现。将IMBL的比值与医学CT的比值进行比较，在医学CT中蝶形滤过器塑造光束轮廓以减少对体表器官的吸收剂量。CTDI比值对空气中的测量值进行缩放，以估计代表单位长度平均剂量的体积CTDI以及代表扫描体积吸收剂量的剂量长度乘积。医学CT剂量计算器使用DLP、光束质量、轴向准直和螺旋螺距来估计器官剂量和有效剂量。医学CT每单位DLP的有效剂量作为身体区域、光束能量以及从新生儿到成人的样本大小的函数给出。
