Rajaraman Vishnukumar, Ponnusamy Madhusudhanan, Halanaik Dhanapathi
Department of Nuclear Medicine, Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry, India.
Asia Ocean J Nucl Med Biol. 2020 Winter;8(1):58-63. doi: 10.22038/aojnmb.2019.40863.1276.
Size specific dose estimate (SSDE) is a new parameter that includes patient size factor in its calculation. Recent studies have produced mixed results on the utility of SSDE, especially when automatic exposure control (AEC) was used. The objective of the study was to find out if there is a relationship between patient size and each of the parameters, SSDE and CTDIvol, when AEC is used.
CT data of consecutively selected 111 patients were included for analysis. CTDIvol values of the CT scans were extracted for each patient. Effective diameter of each patient was calculated as geometric mean of anteroposterior and lateral diameters measured on axial CT images. Corresponding conversion factors for effective diameters were obtained from American Association of Physicists in Medicine (AAPM) report 204. SSDE was obtained as the product of CTDIvol and conversion factor values. Linear regression model was used to evaluate the relationship between patient size and the parameters SSDE and CTDIvol.
Mean weight was 62 (11.5) and range was 34 - 103 kg. Median CTDIvol (mGy) on AEC mode was 7.27(IQ range 7.27, 7.65) and mean effective diameter was 26.2 cm (2.4). Mean SSDE (mGy) was 10.6 (0.84). Good positive correlation was obtained between CTDIvol and effective diameter (r=0.536; p<0.0005). Strong inverse correlation was noted between SSDE and effective diameter (r=-0.777; p<0.0005). Linear regression model for establishing relationship between CTDIvol and effective diameter showed slope of 0.314mGy/cm (R=0.561; R2=0.314; P<0.0005) whereas between effective diameter and SSDE slope was -0.23mGy/cm (R=0.676; R2=0.457; P< 0.0005).
The study shows that CTDIvol and SSDE vary but divergently, with patient size. SSDE is a better estimate of patient radiation dose from CT of MPI SPECT/CT than CTDIvol in systems that use automated exposure control.
特定尺寸剂量估算（SSDE）是一种在计算中纳入患者体型因素的新参数。近期研究对于SSDE的效用得出了不一致的结果，尤其是在使用自动曝光控制（AEC）时。本研究的目的是探究在使用AEC时患者体型与各参数（SSDE和容积CT剂量指数（CTDIvol））之间是否存在关联。
纳入连续选取的111例患者的CT数据进行分析。提取每位患者CT扫描的CTDIvol值。将每位患者的有效直径计算为在轴向CT图像上测量的前后径和侧径的几何平均值。从美国医学物理学家协会（AAPM）报告204中获取有效直径的相应转换因子。SSDE通过CTDIvol与转换因子值的乘积获得。使用线性回归模型评估患者体型与参数SSDE和CTDIvol之间的关系。
平均体重为62（11.5）kg，范围为34 - 103 kg。AEC模式下的CTDIvol中位数（mGy）为7.27（四分位间距7.27，7.65），平均有效直径为26.2 cm（2.4）。平均SSDE（mGy）为10.6（0.84）。CTDIvol与有效直径之间获得了良好的正相关（r = 0.536；p < 0.0005）。SSDE与有效直径之间存在强负相关（r = -0.777；p < 0.0005）。建立CTDIvol与有效直径之间关系的线性回归模型显示斜率为0.314 mGy/cm（R = 0.561；R² = 0.314；P < 0.0005），而有效直径与SSDE之间的斜率为-0.23 mGy/cm（R = 0.676；R² = 0.457；P < 0.0005）。
该研究表明，CTDIvol和SSDE随患者体型而变化，但变化趋势不同。在使用自动曝光控制的系统中，与CTDIvol相比，SSDE能更好地估算MPI SPECT/CT的CT检查中患者接受的辐射剂量。
