背景:螺旋CT扫描中的器官剂量取决于管起始角。
目的:确定单源CT(SSCT)和双源CT(DSCT)扫描中的有效剂量,作为管起始角和螺距值的函数,以通过选择最佳起始角来确定剂量减少潜力。
方法:使用蒙特卡罗模拟,不同管位置的剂量值,角度增量为10〇$10^\\circ$,纵向增量为4.5mm$4.5\\,\\mathrm{m}\\mathrm{m}$在31.5cm$31.5范围内模拟\\,\\mathrm{c}\\mathrm{m}$,准直为40毫米$40\\,\\mathrm{mm}$,60毫米$60\\,\\mathrm{mm}$,和8000万美元80\\,\\mathrm{m}\\mathrm{m}$。根据临床CT数据,对六名成年患者的胸部区域进行了模拟。从所得的剂量分布来看,器官剂量和有效剂量被确定为管角度和纵向位置的函数。使用这些每视图剂量数据,个体器官的剂量,以及总有效剂量,对于有和没有管电流调制(TCM)的螺旋扫描,SSCT的螺距值为0.5至1.5,DSCT的螺距值为3.0。确定最佳和最差管起始角的剂量,并与所有管起始角上的平均剂量进行比较。
结果:随着间距和准直度的增加,在所有开始角度上平均的有效剂量的剂量变化增加。而对于4000万美元的准直,40美元,\\mathrm{m}\\mathrm{m}$,对于SSCT,平均剂量值的变化保持在5%$5\\%$以下,我们发现,对于带有TCM的DSCT的螺距为3.0的螺旋扫描,准直为80mm$80\,\\mathrm{m}\\mathrm{m}$,最佳起始角度的剂量平均比平均值低16%$16\\%$,比最大值低28%$28\\%$。
结论:螺旋扫描中管起始角的变化显示出辐射剂量的实质性差异,特别是对于高螺距值和高准直。因此,我们建议控制导管起始角度以降低患者风险。
BACKGROUND: Organ doses in spiral CT scans depend on the tube start angle.
OBJECTIVE: To determine the effective dose in single source CT (SSCT) and dual source CT (DSCT) scans as a function of tube start angle and spiral pitch value to identify the dose reduction potential by selecting the optimal start angle.
METHODS: Using Monte Carlo simulations, dose values for different tube positions with an angular increment of 10 ∘ $10^\\circ$ and a longitudinal increment of 4.5 m m $4.5 \\,\\mathrm{m}\\mathrm{m}$ were simulated over a range of 31.5 c m $31.5 \\,\\mathrm{c}\\mathrm{m}$ with collimations of 40 mm $40\\, \\mathrm{mm}$ , 60 mm $60\\, \\mathrm{mm}$ , and 80 m m $80 \\,\\mathrm{m}\\mathrm{m}$ . The simulations were performed for the thorax region of six adult patients based on clinical CT data. From the resulting dose distributions, organ doses and effective dose were determined as a function of tube angle and longitudinal position. Using these per-view dose data, the individual organ doses, as well as the total effective dose, were determined for spiral scans with and without tube current modulation (TCM) with pitch values ranging from 0.5 to 1.5 for SSCT and up to 3.0 for DSCT. The dose of the best and worst tube start angle in terms of dose was determined and compared to the mean dose over all tube start angles.
RESULTS: With increasing pitch and collimation, the dose variations from the effective dose averaged over all start angles increase. While for a collimation of 40 m m $40 \\,\\mathrm{m}\\mathrm{m}$ , the variations from the mean dose value stay below 5 % $5 \\%$ for SSCT, we find that for a spiral scan with a pitch of 3.0 for DSCT with TCM and collimation of 80 m m $80 \\,\\mathrm{m}\\mathrm{m}$ , the dose for the best starting angle is on average 16 % $16 \\%$ lower than the mean value and 28 % $28 \\%$ lower than the maximum value.
CONCLUSIONS: Variation of the tube start angle in spiral scans exhibits substantial differences in radiation dose especially for high pitch values and for high collimations. Therefore, we suggest to control the tube start angle to minimize patient risk.