成年受检者数字断层融合扫描有效剂量估算

目的 估算数字断层融合扫描时组织、器官吸收剂量和受检者有效剂量,为辐射剂量学提供数据参考。方法 按照受检者检查部位（主射束扫描部位）将体模实验分组,以放射科现场收集的数字断层融合扫描人体不同部位时实时显示的数据作为体模实验的条件,对体模进行扫描,计算组织、器官的吸收剂量,并估算成年受检者的有效剂量。结果 成年受检者采用数字断层融合扫描时有效剂量分别为头部组0.524 mSv、颈椎组0.736 mSv、胸椎组2.719 mSv、胸部组1.810 mSv、腰椎组1.240 mSv、腹部组2.317 mSv、骨盆组2.316 mSv。结论 数字断层融合扫描时,成年受检者有效剂量的估算结果为胸椎组最高,其次为腹部组,头部组最小,有效剂量主要相关因素为管电压、总mAs、照射野大小、主射束照射范围、扫描范围内组织或器官的数量。     

儿童胸部CT扫描时腹部屏蔽方法与效果研究

目的 研究儿童胸部CT扫描时腹部的屏蔽方法及其效果。方法 用美国CIRS公司生产的5岁儿童体模代替儿童受检者,在腹部内布放热释光剂量计LiF（Mg,Cu,P）,按儿童胸部CT扫描的通常程序对体模进行扫描,测量在无屏蔽、用铅衣覆盖和用铅衣包裹时腹腔内主要器官与组织的剂量。结果 儿童胸部CT扫描时,腹腔内部分器官的吸收剂量可达到数mGy。3种扫描之间,相同位置处的剂量值差异有统计学意义（χ²=16.00,P<0.05）;正面覆盖和包裹屏蔽方式之间的剂量值差异有统计学意义（Z=-2.52,P<0.05 ）。较之于无屏蔽措施,采用0.35 mm铅衣包裹腹部,可分别降低睾丸和结肠的剂量71.2%和42.3%,采用同样当量铅衣铺盖腹部剂量可降低55.9%和26.1%。结论 开展儿童胸部CT扫描时,使用铅防护衣可有效屏蔽腹部受照,对性腺和结肠的防护具有重要作用,特别是包裹式的屏蔽措施值得推荐。     

基于中国参考人的典型CT扫描患者剂量模拟与分析

目的 基于中国参考人体模,对典型CT患者剂量进行模拟与分析。开发一款在线评估CT扫描所致受检者器官吸收剂量和有效剂量的软件,为快速评估CT扫描辐射剂量提供工具。方法 采用蒙特卡罗方法,对GE LightSpeed 16型号CT进行建模,基于中国参考人体模计算中国成年男性、女性和1岁儿童受CT扫描照射后各组织器官的剂量,建立单层轴扫器官剂量数据库。开发基于web的CT剂量评估软件,根据用户输入的CT扫描参数,从器官剂量数据库中读取数据并快速计算器官吸收剂量和有效剂量。结果 开发了一款新的CT扫描剂量评估软件,可用于评估中国成年男女和1岁儿童在不同型号CT检查中,不同管电压、管电流、准直器宽度等CT参数下的器官剂量。CT扫描剂量评估软件的计算结果与两个文献数据进行对比,对于完全包含在扫描范围内的器官剂量差异较小,相对差异分别在15%和25%以内。结论 CT扫描剂量评估软件为简单快速评估CT扫描辐射剂量提供了有力的工具。     

5岁儿童仿真模体千伏锥束CT模拟剂量测量

目的 利用热释光探测器（TLD）在CIRS 5岁仿真儿童模体内测量瓦里安千伏锥束CT（kV-CBCT）标准扫描参数下各重要器官剂量,并以此计算有效剂量。方法 挑选一致性在2%以内的TLD并退火。首先基于相同骨盆扫描模式分别用CT电离室和TLD测量CIRS骨盆仿真模体相同体积内的剂量和读数,二者比值即为TLD转换系数;将夹在组织等效插件中的TLD放入儿童模体器官内预留的插孔,在头部、胸部和骨盆3种标准扫描条件模式下,测量器官剂量,并计算有效剂量。结果 TLD转换系数是3.91 mGy/每读数;在头部、胸部和骨盆3种标准扫描条件下,得出全身有效剂量分别是0.63、6.85和19.3 mSv。结论 用CT电离室刻度过的TLD测量kV-CBCT给儿童仿真模体带来的辐射剂量的方法具有可行性。本研究中骨盆扫描条件的有效剂量高于胸部和头部,即该条件预期产生的辐射危害较大,诱发继发性癌症风险较高。     

CT头颈部检查所致婴幼儿眼晶状体吸收剂量估算方法的模体研究

目的 探讨CT不同扫描方案检查所致婴幼儿眼晶状体吸收剂量估算方法,并寻求快速估算眼晶状体吸收剂量的实用方法。方法 通过设置7种临床标准扫描方案,对1岁年龄组仿真模体进行扫描,利用布放在模体不同位置的热释光探测器（TLD）测量剂量,最后测量结果分别用组织因子转换和个人剂量当量转换两种方法来估算眼晶状体吸收剂量,同时将眼晶状体吸收剂量与CT剂量指数（CTDI）建立线性回归方程。结果 7种临床标准儿童扫描方案CT检查所致的婴幼儿眼晶状体吸收剂量分别为（9.96±0.69）mGy（头部轴向）、（7.01±0.42）mGy（头部螺旋）、（12.60±0.97）mGy（副鼻窦）、（12.97±0.42）mGy（内耳高分辨）、（0.63±0.03）mGy（颈部软组织）、（8.89±0.44）mGy（颈部颈椎）和（0.34±0.01）mGy（胸部常规）,不同组之间剂量差异有统计学意义（F=846.826,P<0.05）。不同扫描部位,CTDI值与眼晶状体吸收剂量之间均存在线性关系（r=0.986~0.999,P<0.05）。结论 采用儿童CT扫描条件,婴幼儿眼晶状体吸收剂量单次剂量范围一般不会超过阈剂量。另外,通过读取CTDI值,利用线性关系,可快速估算眼晶状体吸收剂量。     

苏州市数字X射线摄影和CT医疗照射所致公众剂量负担的研究

目的 估算2017年苏州市医用数字X射线摄影（DR）和CT所致全市公众有效剂量负担。方法 利用分层随机抽样方法,通过医学影像存档与通信系统（PACS）和放射科信息系统（RIS）,采集苏州市27家医疗机构2017年DR和CT诊疗频度数据。对于DR,使用剂量面积乘积测量仪测量受检者常见投照部位的剂量面积乘积（DAP）,估算出有效剂量;对于CT,测量头部、胸部和腹部扫描时的加权CT剂量指数（CTDI_w）,结合扫描参数,估算出有效剂量。根据各部位的扫描人次和有效剂量,估算苏州市DR和CT医疗照射所致公众剂量负担。结果 DR检查中,腹部前后位、骨盆前后位、头颅侧位和后前位、胸部侧位和后前位、胸椎侧位和后前位、腰椎侧位和后前位一次检查所致受检者有效剂量分别为0.565、0.280、0.016、0.012、0.111、0.060、0.100、0.102、0.307和0.152 mSv。CT检查中,头部、胸部、腹部一次检查所致受检者有效剂量分别为1.33、5.75和7.31 mSv。2017年苏州市DR和CT医疗照射所致公众剂量为9 593.07人·Sv,人均年有效剂量为0.898 mSv。结论 CT医疗照射对公众剂量的贡献量远大于DR照射的贡献量。苏州市DR和CT医疗照射所致公众剂量负担处于高水平,需要引起相关卫生行政部门的重视。     

兆伏级锥形束CT图像引导放疗所致鼻咽癌患者剂量的探讨

目的 评价和估算兆伏级锥形束CT(MV CBCT)成像系统在图像引导放疗中所致鼻咽癌患者的辐射剂量。方法 选择MV CBCT系统头颈部8 MU扫描预案,利用0.65 cm³指型电离室和CT头部剂量体模测量出体模不同位置的吸收剂量。并利用XiO治疗计划系统模拟MV CBCT扫描过程,计算体模电离室测量点的吸收剂量和鼻咽癌患者肿瘤靶区及危及器官的吸收剂量。结果 体模不同位置吸收剂量的测量值和计算值具有很好的一致性,相对误差均小于3.5%。MV CBCT图像引导放疗所致鼻咽癌患者肿瘤靶区平均剂量为6.43 cGy,脑干、脊髓和视交叉的平均剂量分别为6.36 、6.83和6.90 cGy,左、右视神经平均剂量分别为7.70和7.53 cGy,左、右腮腺平均剂量分别为6.86和6.43 cGy。结论 使用治疗计划系统模拟MV CBCT图像采集过程估算剂量准确、可靠。在设计患者治疗计划时,要充分考虑MV CBCT图像采集过程所致患者剂量。     

儿童CT检查中扫描参数的优化

目的 了解儿童CT检查扫描条件选择及其所致辐射剂量的相关性,以期通过适当调节mAs、扫描长度等参数,降低儿童CT检查患者受照剂量。方法 比较江苏省7家医院不同年龄组（<1岁、1~5岁、6~10岁和11~15岁）儿童头颅、胸部、腹部多排螺旋CT检查主要扫描参数的差异。选用相同的检查参数在TM160剂量模体上测量CTDI₁₀₀,计算DLP,并通过经验加权因子,估算出不同部位检查的有效剂量（E）。对mAs、扫描长度和DLP进行多元线性回归分析,比较两家典型医院由于选择扫描条件不同所导致的剂量差异。结果 儿童头颅、胸部、腹部CT检查所致患者的有效剂量均值分别为2.46、5.69、11.86 mSv,各部位检查DLP与mAs、扫描长度均呈正相关（r=0.81、0.81、0.92,P<0.05）。较高的mAs选择,致使本研究各年龄组儿童胸腹部CT检查有效剂量是德国Galanski等研究的1.2~3.0倍;B医院各年龄组腹部检查选择了较高的扫描长度,以致其所致有效剂量均高于本研究均值。结论 建议通过合理优化儿童不同部位CT检查mAs、扫描长度等扫描参数,降低受检者所受辐射风险。     

婴儿头颅CT中铋屏蔽对辐射剂量和影像质量的影响

目的 研究婴儿头颅CT检查中使用铋屏蔽材料降低眼晶状体受照剂量的效果及对图像质量的影响。方法 使用适合患儿使用的自制铋屏蔽防护眼罩、婴儿体模,采用热释光探测器测量受照剂量。CT扫描条件选择120 kV、130 mA轴位扫描,分别进行铋屏蔽和无屏蔽两组模体测试,比较模体内相当于晶状体位置的受照剂量;应用同样CT扫描参数,对临床疑为颅内出血的99例患儿佩戴铋屏蔽眼罩后进行头部扫描,由2名高年资医生分别进行图像质量评估,并比较评分的一致性。结果 体模实验显示,无屏蔽时眼罩后方区域吸收剂量为25 mGy,经铋防护眼罩屏蔽后眼罩后方的吸收剂量为17 mGy,降低辐射剂量32%。佩戴铋屏蔽眼罩对患儿头部CT图像质量无明显影响。结论 在婴儿头颅CT扫描中使用铋屏蔽防护眼罩,可明显降低眼晶状体放射吸收剂量,同时对CT图像质量的影响是可接受的。     

不同扫描中心结合自动管电流调制技术和自动管电压调制技术在CT扫描中对辐射剂量影响的模体研究

目的 探讨在应用自动管电流调制技术（ATCM）和自动管电压调制技术（CARE kV）行头颈部和胸部CT螺旋扫描时,不同扫描中心对辐射剂量的影响。方法 联合ATCM和CARE kV技术,对头颈部和胸部模体行CT螺旋扫描。头颈部模体选取眼球中心向上4 cm、眼球、眼球与外耳孔连线中点、外耳孔、外耳孔向下5 cm 5种不同的扫描中心（即不同检查床高度）,胸部模体选取乳腺向上5 cm和4 cm、乳腺、腋前线、腋中线、腋后线6种不同的扫描中心。每种扫描中心时定位像扫描3次,然后1次螺旋扫描。头颈部模体在眼眶中心及第5颈椎（C5）椎体上缘层面选取感兴趣区（ROI）,胸部模体在肺尖及气管分叉层面选取ROI,测量记录对比噪声比（CNR）。用热释光剂量计（TLD）测量每次扫描时眼晶状体和乳腺的器官剂量。记录每次扫描的容积CT剂量指数（CTDI_vol）。结果 头颈部模体5种不同扫描中心时,眼晶状体累积辐射剂量最高在眼球与外耳孔连线中点为中心（8.851 mGy）,CTDI_vol最高在外耳孔向下5 cm为中心（15.850 mGy）。眼晶状体累积辐射剂量最低在外耳孔向下5 cm为中心（7.096 mGy）,CTDI_vol最低在眼球、眼球与外耳孔连线中点、外耳孔为中心（均为15.380 mGy）。胸部模体6种不同扫描中心时,乳腺累积辐射剂量最高在乳腺为中心（6.467 mGy）,CTDI_vol最高在腋前线为中心（4.120 mGy）。腋后线为中心上述值最低（分别为4.794和3.540 mGy）。头颈部模体眼眶中心层面、C5椎体上缘层面的CNR分别为87.22~108.88和136.13~175.57;胸部模体肺尖层面、气管分叉处层面的CNR分别为75.19~116.92和42.85~86.78。结论 CT扫描中心的选择对CT扫描部位的辐射剂量,特别是对射线敏感的组织和器官的辐射剂量有很大影响。     

Analysis of effective and organ dose estimation in CT when using mA modulation: A single scanner pilot study

IntroductionEffective dose (ED) estimation in CT examinations can be obtained by combining dose length product (DLP) with published ED per DLP coefficients or performed using software. These methods do not account for tube current (mA) modulation which is influenced by patient size. The aim of the work was to compare different methods of organ and ED estimation to measured values when using mA modulation in CT chest, abdomen and pelvis examinations.MethodOrgan doses from CT of the chest, abdomen and pelvis were measured using digital dosimeters and a dosimetry phantom. ED was calculated. Six methods of estimating ED accounting for mA modulation were performed using ImPACT CTDosimetry and Dose Length Product to ED coefficients. Corrections for the phantom mass were applied resulting in 12 estimation methods. Estimated organ doses from ImPACT CTDosimtery were compared to measured values.ResultsCalculated EDs were; chest 12.35 mSv (±1.48 mSv); abdomen 8.74 mSv (±1.36 mSv) and pelvis 4.68 mSv (±0.75 mSv). There was over estimation in all three anatomical regions. Correcting for phantom mass improved agreement between measured and estimated ED. Organ doses showed overestimation of dose inside the scan range and underestimation outside the scan range.ConclusionReasonable estimation of effective dose for CT of the chest and abdomen can be obtained using ImPACT CTDosimetry software or k-coefficients. Further work is required to improve the accuracy of ED estimation from CT of the pelvis. Accuracy of organ dose estimation has been shown to depend on the inclusion or exclusion of the organ from the scan range.     

加速器MVCBCT扫描图像在自适应放疗中应用的可行性研究

目的 探讨加速器成像射束影像系统（IBL）的全扇形束和大射野（EFOV）两种模式扫描得到的兆伏级锥形束断层（MV CBCT）图像可否用于剂量计算。方法 利用大孔径CT和在IBL的全扇形束和EFOV模式下对CIRS 062M型电子密度模体进行扫描,在Pinnacle计划系统中分别建立电子密度曲线。用CT和加速器MV级CBCT模式扫描头颈、胸、腹盆腔部仿真模体,利用CT图像制作调强计划,并将计划移植于MV CBCT的图像中,利用相应的电子密度曲线计算剂量,比较靶区及危及器官剂量分布。结果 MV CBCT图像中剂量分布比参考计划剂量偏低,并且在头颈、胸、腹盆腔模体中偏差依次增大。与参考计划相比,头颈部靶区剂量和危及器官剂量分布一致,偏差均在3%以内。胸部和腹盆腔靶区和危及器官的剂量分布均有大幅度的降低,偏差分别达到5%和10%,超出了临床接受范围。结论 在加速器IBL中全扇形束模式条件下,头颈部患者扫描得到的MV CBCT图像可在自适应放疗中用于剂量计算,胸、腹盆腔部位在EFOV模式下仅可用于图像引导,不能用于剂量计算。     

Radiation dose and cancer risk from pediatric CT examinations on 64-slice CT: A phantom study

Objective

To measure the radiation dose from CT scans in an anthropomorphic phantom using a 64-slice MDCT, and to estimate the associated cancer risk.

Materials and methods

Organ doses were measured with a 5-year-old phantom and thermoluminescent dosimeters. Four protocols; head CT, thorax CT, abdomen CT and pelvis CT were studied. Cancer risks, in the form of lifetime attributable risk (LAR) of cancer incidence, were estimated by linear extrapolation using the organ radiation doses and the LAR data.

Results

The effective doses for head, thorax, abdomen and pelvis CT, were 0.7 mSv, 3.5 mSv, 3.0 mSv, 1.3 mSv respectively. The organs with the highest dose were; for head CT, salivary gland (22.33 mGy); for thorax CT, breast (7.89 mGy); for abdomen CT, colon (6.62 mGy); for pelvis CT, bladder (4.28 mGy). The corresponding LARs for boys and girls were 0.015-0.053% and 0.034-0.155% respectively. The organs with highest LARs were; for head CT, thyroid gland (0.003% for boys, 0.015% for girls); for thorax CT, lung for boys (0.014%) and breast for girls (0.069%); for abdomen CT, colon for boys (0.017%) and lung for girls (0.016%); for pelvis CT, bladder for both boys and girls (0.008%).

Conclusion

The effective doses from these common pediatric CT examinations ranged from 0.7 mSv to 3.5 mSv and the associated lifetime cancer risks were found to be up to 0.16%, with some organs of higher radiosensitivity including breast, thyroid gland, colon and lungs.     

A comparison of the CT-dosimetry software packages based on stylized and boundary representation phantoms

IntroductionWith the rapid development of computed tomography (CT) equipment, the assessment of effective and organ dose using suitable tools becomes an important issue and will provide health professionals with useful information regarding the radiation risks and the development of standard imaging protocols. Different clinical centres and/or institutions may use several software packages, each with different methods and algorithms for CT dose evaluation. Consequently, radiation doses calculated with these computer software packages might be different for the same patient and representative scanner models.MethodsThe effective and organ doses calculated by VirtualDose, CT-expo, and ImPACT software were compared for both males and females using kidney, chest, head, pelvis, abdomen, and whole-body CT protocols. The calculation of radiation dose in these software depends on the use of stylized and boundary representation (BREP) phantoms.ResultsIn general, the results showed that there was a discrepancy between the effective dose values calculated by the three packages. The effective dose in all examinations varied by factors ranging from 1.1 to 1.5 for male and from 1.1 to 1.3 for female. For the female phantom, the VirtualDose shows the highest effective doses in kidney and abdomen examinations while CT-expo gives the highest doses for head and pelvis examinations. For the male phantom, the VirtualDose shows the highest effective doses were for chest examinations.ConclusionVirtualDose approach gives the most accurate estimation, however, further work using a size-based method are necessary to improve the assessment of the effective and equivalent organ dose in CT examinations using these packages.Implications for practiceThe re-evaluation dosimetry software in comparison with patient size would allow for a more accurate estimation of dose and support the optimization process.     

Radiation dose evaluation in 64-slice CT examinations with adult and paediatric anthropomorphic phantoms

The objective of this study was to evaluate the organ dose and effective dose to patients undergoing routine adult and paediatric CT examinations with 64-slice CT scanners and to compare the doses with those from 4-, 8- and 16-multislice CT scanners. Patient doses were measured with small (<7 mm wide) silicon photodiode dosemeters (34 in total), which were implanted at various tissue and organ positions within adult and 6-year-old child anthropomorphic phantoms. Output signals from photodiode dosemeters were read on a personal computer, from which organ and effective doses were computed. For the adult phantom, organ doses (for organs within the scan range) and effective doses were 8–35 mGy and 7–18 mSv, respectively, for chest CT, and 12–33 mGy and 10–21 mSv, respectively, for abdominopelvic CT. For the paediatric phantom, organ and effective doses were 4–17 mGy and 3–7 mSv, respectively, for chest CT, and 5–14 mGy and 3–9 mSv, respectively, for abdominopelvic CT. Doses to organs at the boundaries of the scan length were higher for 64-slice CT scanners using large beam widths and/or a large pitch because of the larger extent of over-ranging. The CT dose index (CTDI_vol), dose–length product (DLP) and the effective dose values using 64-slice CT for the adult and paediatric phantoms were the same as those obtained using 4-, 8- and 16-slice CT. Conversion factors of DLP to the effective dose by International Commission on Radiological Protection 103 were 0.024 mSv⋅mGy⁻¹⋅cm⁻¹ and 0.019 mSv⋅mGy⁻¹⋅cm⁻¹ for adult chest and abdominopelvic CT scans, respectively.X-ray CT scanners have made remarkable advances over the past few years, contributing to the improvement of diagnostic image quality and the reduction of examination time. CT scanners with 64 slices, the clinical use of which started quite recently in many medical facilities, has enabled a large number of thin slices to be acquired in a single rotation. 64-slice CT technology accelerated the practical use of three-dimensional body imaging techniques such as coronary CT angiography and CT colonography with an increasing number of CT examinations. The increase in CT examination frequency not only for adults but also for children and the higher doses in CT examinations compared with other X-ray diagnostic procedures have raised concerns about patient doses and safety. An understanding of patient doses requires the evaluation of organ and effective doses for patients undergoing CT examinations, although these dose values in 64-slice CT scans have seldom been reported.One common method for estimating organ and effective doses is dose calculation from the CT dose index (CTDI) or dose–length product (DLP), which are both used as readily available indicators of radiation dose in CT examinations. Organ and effective doses can be estimated from the CTDI or DLP, and conversion factors derived from Monte Carlo simulation of photon interactions within a simplified mathematical model of the human body [1]. Another method is based on measurement using thermoluminescence dosemeters (TLDs) implanted in various organ positions within an anthropomorphic phantom [2–6]. Although TLD dosimetry is considered to be the standard method for measuring absorbed doses in a phantom, the dose measurement is laborious and time consuming. Hence, we devised an in-phantom dosimetry system using silicon photodiode dosemeters implanted in various organ positions, where absorbed dose at each position could be read electronically. In the present study, we evaluated organ and effective doses with 64-slice CT scan protocols used clinically for adult and paediatric patients undergoing chest and abdominopelvic CT examinations. We compared the doses with published dose values for 4-, 8- and 16-slice CT, and indicated the conversion factor of DLP to the effective dose in each examination of the chest and abdomen–pelvis for 64-slice CT scanners.     

A dose comparison survey in CT departments of dedicated paediatric hospitals in Australia and Saudi Arabia

AIM: To measure and compare computed tomography (CT) radiation doses delivered to patients in public paediatric hospitals in Australia and Saudi Arabia. METHODS: Doses were measured for routine CT scans of the head, chest and abdomen/pelvis for children aged 3-6 years in all dedicated public paediatric hospitals in Australia and Saudi Arabia using a CT phantom measurement cylinder.RESULTS: CT doses, using the departments’ protocols for 3-6 year old, varied considerably between hospitals. Measured head doses varied from 137.6 to 528.0 mGy·cm, chest doses from 21.9 to 92.5 mGy·cm, and abdomen/pelvis doses from 24.9 to 118.0 mGy·cm. Mean head and abdomen/pelvis doses delivered in Saudi Arabian paediatric CT departments were significantly higher than those in their Australian equivalents. CONCLUSION: CT dose varies substantially across Australian and Saudi Arabian paediatric hospitals. Therefore, diagnostic reference levels should be established for major anatomical regions to standardise dose.     

Clinical indications and utilization of 320-detector row CT in 2500 outpatients

Clinical indications and utilization patterns for 3963 CT scans on 2500 consecutive patents on a 320-detector row CT in an outpatient setting were retrospectively analyzed and compared with previously reported CT studies. The impact of the latest generation CT technology, including whole organ perfusion, on indications and utilization patterns during the study period was also assessed. The top five requested CT scan types were abdomen/pelvis, chest, head, sinuses, and coronary CT angiography. Indication and utilization rates were similar to prior studies for abdomen/pelvis, non-cardiac chest, and head CT scans. Abdominal pain and headaches were the most frequent indications for abdomen/pelvis and head CTs, respectively. The 7.3% cardiac CT scan utilization rate was not comparable to rates of up to 72% in self-referral outpatient settings. Whole organ volume CT imaging was utilized in 100% of coronary CT angiography and 22.7% of head CTs. The 320-row CT had fewer negative head and body CT findings as compared to prior reports. The availability of new technology, such as whole organ dynamic scans, appears to have influenced CT indications, utilization and finding rates with a decrease in negative brain and body results. Comparisons with previous outpatient CT studies were similar for multiple categories with the exception of cardiac CT utilization, which is heavily influenced by self-referral. Further study of outpatient imaging indications and utilization rates from multiple centers may benefit from a standardized categorization to improve understanding of the disparate outpatient imaging environment.     

X射线摄影所致受检者器官剂量-入射体表剂量转换系数的研究

目的 比较简单程式化数学模型(MIRD)与体素模型在常见X射线摄影下得到的器官剂量-入射体表剂量的转换系数差异。方法 利用蒙特卡罗模拟技术,分别模拟计算体素模型的5种常见摄影下受检者的器官剂量与入射体表剂量,并计算两者的转换系数,与MIRD模型所得结果进行比较。结果 体素模型得到射野内器官的转换系数分别是,胸部后前位0.149~0.650,胸部左侧位0.067~0.382,胸部右侧位0.023~0.374,腹部前后位0.035~0.431,腰椎前后位0.083~0.432。在胸部后前位下,两种模型模拟肺的剂量转换系数结果相差最大约54.3%;胸部左侧位照射的肝脏剂量转换系数差异最大为54.5%;胸部右侧位照射胃剂量转换系数差异最大为63.8%;而腹部前后位,两种模型模拟脾脏的剂量转换系数差异最大为65.0%;腰椎前后位发现胃的剂量转换系数相差最大约43.7%。结论 利用两种模型模拟得到的器官剂量转换系数偏差可达50%以上,由于MIRD模型的解剖结构过于简化,计算误差较大。利用体素模型得到的转换系数数据更加科学合理。     

Organ and effective dose reduction in adult chest CT using abdominal lead shielding

Objectives

The purpose of this study was to evaluate and compare organ and effective dose savings that could be achieved using conventional lead aprons and a new, custom-designed shield as out-of-plane shielding devices during chest CT scans.

Methods

Thermoluminescent dosimeters were used to measure doses throughout the abdomen and pelvis during CT scans of the chest of a RANDO phantom. Dose measurements were made with no shielding, with lead aprons and with the new shield around the abdomen and pelvis in order to quantify the achievable organ and effective dose reductions.

Results

Average dose savings in the 10 phantom sections ranged from 5% to 78% with the highest point dose saving of 93% being found in the mid-pelvis. When shielding was used, the maximum measured organ dose reduction was a 72% dose saving to the testes. Significant dose savings were found throughout the abdomen and pelvis, which contributed to an effective dose saving of 4% that was achieved over and above the dose savings obtained through conventional optimisation strategies. This could yield significant population dose savings and reductions in collective radiation risk.

Conclusion

In this study significant organ and effective dose reductions have been achieved through the use of abdominal shielding during chest CT examinations and it is therefore recommended that out-of-plane patient shielding devices should be used for all chest CT scans and potentially for every CT scan, irrespective of body part.Good radiographic practice aims to ensure that patient radiation dose from any examination is kept as low as reasonably practicable (ALARP) [1] as long as the image quality is consistent with the intended purpose of the examination. There are many steps that can be taken in order to reduce the radiation dose on a patient-by-patient basis. One such method is to place radiation-absorbing material, usually in the form of lead rubber shielding, onto the patient surface, outside of the anatomy of interest. Shielding in this manner has been used in dental and conventional radiology as well as fluoroscopy and has been shown to yield significant dose savings [2-7]. This technique, referred to as “out-of-plane” shielding, has also been advocated in CT for protection of the breast and thyroid [8-12]. However, the main use of such shielding has been in protecting the foetus of pregnant patients undergoing head, neck, chest or extremity CT scans. There has been uncertainty whether or not such shielding results in a decrease or increase in the foetal radiation dose due to the potential for increased internal scatter from the shields. Hidajat et al [10] reported no reduction in the dose to the uterus and ovaries when a thin lead shield was used during a scan of the upper abdomen. This, along with further anecdotal evidence, has caused debate over the effectiveness of out-of-plane shielding in CT.In recent years a number of papers have shown that abdominal shielding yields foetal dose reductions of approximately 35% in both early and late stage pregnancy when patients undergo chest CT [13-15]. Despite this evidence, out-of-plane shielding has not been used regularly in CT scanning even though the use of such shielding has no effect on the quality of the images produced.Recent publications have brought the issue of radiation dose in CT to the forefront of thinking in the radiology community. In late 2009 Smith-Bindman et al [16] showed that for each examination type there was an average 13-fold variation between the highest and lowest radiation doses from standard CT scans in four hospitals in the San Francisco Bay Area, CA. Further analysis showed that the risk of cancer induction from CT scans was highest for coronary angiography scans of 20-year-old women where 1 cancer could potentially be induced per 150 patient examinations.Concern was also expressed following the publication of Berrington de Gonzalez et al [17], who sought to quantify the number of cases of cancer that could be attributed to CT scanning in the United States during 2007. It was estimated that 29 000 cancers could be related to CT scans of which 14 000 resulted from abdomen/pelvis scans, 4100 resulted from chest scans, 4000 resulted from head CT and a further 2700 from chest CT angiography. Given the rapid development in scanning technology it is likely that the number of scans performed in 2008 and 2009 is higher than the reported figures of 70 million CT scans for 2007 and, as such, the number of cancers induced could be greater than the 29 000 figure for 2007.The advent of multislice CT (MSCT) has increased the range of examinations that can be performed, and as such Fazer et al [18] now estimate that in the United States approximately 50% of the collective effective dose resulting from medical procedures is attributable to CT scanning. Similarly in the UK approximately 47% of the collective dose from medical procedures is attributable to CT scanning [19].