Application of European Commission reference dose levels in CT examinations in Crete, Greece

The purpose of this study was to apply European Commission reference dose levels (EC RDLs) to routine CT examinations. The dosimetric quantities proposed in the European Guidelines (EG) for CT are weighted computed tomography dose index (CTDI(w)) for a single slice and dose-length product (DLP) for a complete examination. Patient-related data as well as technical parameters for brain, chest, abdomen and pelvis examinations were collected for four CT scanners in the Euromedica Medical Center. Computed tomography dose index (CTDI) measurements were performed on each scanner and CTDI(w), DLP and effective dose E were estimated for each type of examination for a random sample of 10 typical patients. Mean values of CTDI(w) had a range of 27.0-52.0 mGy for brain and 13.9-26.9 mGy for chest, abdomen and pelvis examinations. Mean values of DLP had a range of 430-758 mGy cm for brain, 348-807 mGy cm for chest, 278-582 mGy cm for abdomen and 306-592 mGy cm for pelvis examinations. Mean values of E were 1.4 mSv for brain, 10.9 mSv for chest, 7.1 mSv for abdomen and 9.3 mSv for pelvis examinations. Results confirm that the Euromedica Medical Center meets EC RDLs for brain, abdomen and pelvis examinations, in terms of radiation dose and examination technique. As far as chest examination is concerned, although CTDI(w) of each scanner is within proposed values, the DLP is consistently exceeded, probably because of the large irradiation volume length L. It is anticipated that a reduction of L, or product mAs, or their combination, will reduce DLP without affecting image quality.     

Variations in radiation dose between the same model of multislice CT scanner at different hospitals

The variation in exposure factors and patient dose, between seven centres using identical multislice CT scanners, was investigated for six standard examinations. Dose values were compared with each other and the relevant diagnostic reference level (DRL) for each examination. The range in weighted CT dose index (CTDI(w)) values between the seven centres was small for abdominal scans and head scans. For other scans however, such as functional endoscopic sinonasal surgery (FESS) the variations in CTDI(w) were as high as a factor of seven between the lowest and the highest values. At one centre a program of dose optimization had been undertaken and this centre had CTDI(w) values ranging from 3% to 64% lower than the average value for the seven centres. This demonstrates that significant dose reduction can be achieved through close collaboration between medical physicists, radiologists and radiographers.     

National survey of doses from CT in the UK: 2003

A review of patient doses from CT examinations in the UK for 2003 has been conducted on the basis of data received from over a quarter of all UK scanners, of which 37% had multislice capability. Questionnaires were employed to collect scan details both for the standard protocols established at each scanner for 12 common types of CT examination on adults and children, and for samples of individual patients. This information was combined with published scanner-specific CT dose index (CTDI) coefficients to estimate values of the standard dose indices CTDI(w) and CTDI(vol) for each scan sequence. Knowledge of each scan length allowed assessment of the dose-length product (DLP) for each examination, from which effective doses were then estimated. When compared with a previous UK survey for 1991, wide variations were still apparent between CT centres in the doses for standard protocols. The mean UK doses for adult patients were in general lower by up to 50% than those for 1991, although doses were slightly higher for multislice (4+) (MSCT) relative to single slice (SSCT) scanners. Values of CTDI(vol) for MSCT were broadly similar to European survey data for 2001. The third quartile values of these dose distributions have been used to derive UK national reference doses for examinations on adults (separately for SSCT and MSCT) and children as initial tools for promoting patient protection. The survey has established the PREDICT (Patient Radiation Exposure and Dose in CT) database as a sustainable national resource for monitoring dose trends in CT through the ongoing collation of further survey data.     

Validation of a Monte Carlo tool for patient-specific dose simulations in multi-slice computed tomography

Estimating the dose delivered to the patient in X-ray computed tomography (CT) examinations is not a trivial task. Monte Carlo (MC) methods appear to be the method of choice to assess the 3D dose distribution. The purpose of this work was to extend an existing MC-based tool to account for arbitrary scanners and scan protocols such as multi-slice CT (MSCT) scanners and to validate the tool in homogeneous and heterogeneous phantoms. The tool was validated by measurements on MSCT scanners for different scan protocols under known conditions. Quantitative CT Dose Index (CTDI) measurements were performed in cylindrical CTDI phantoms and in anthropomorphic thorax phantoms of various sizes; dose profiles were measured with thermoluminescent dosimeters (TLD) in the CTDI phantoms and compared with the computed dose profiles. The in-plane dose distributions were simulated and compared with TLD measurements in an Alderson-Rando phantom. The calculated dose values were generally within 10% of measurements for all phantoms and all investigated conditions. Three-dimensional dose distributions can be accurately calculated with the MC tool for arbitrary scanners and protocols including tube current modulation schemes. The use of the tool has meanwhile also been extended to further scanners and to flat-detector CT.     

Establishment of CT diagnostic reference levels in Ireland

Objective To propose Irish CT diagnostic reference levels (DRLs) by collecting radiation doses for the most commonly performed CT examinations. Methods A pilot study investigated the most frequent CT examinations. 40 CT sites were then asked to complete a survey booklet to allow the recording of CT parameters for each of 9 CT examinations during a 12-week period. Dose data [CT volume index (CTDI(vol)) and dose-length product (DLP)] on a minimum of 10 average-sized patients in each category were recorded to calculate a mean site CTDI(vol) and DLP value. The rounded 75th percentile was used to calculate a DRL for each site and the country by compiling all results. Results are compared with international DRL data. Results Data were collected for 3305 patients. 30 sites responded with data for 34 scanners, representing 54% of the national total. All equipment had multislice capability (2-128 slices). DRLs are proposed using CTDI(vol) (mGy) and DLP (mGy cm) for CT head (66/58 and 940, respectively), sinuses (16 and 210, respectively), cervical spine (19 and 420, respectively), thorax (9/11 and 390, respectively), high resolution CT (7 and 280, respectively), CT pulmonary angiography (13 and 430, respectively), multiphase abdomen (13 and 1120, respectively), routine abdomen/pelvis (12 and 600, respectively) and trunk examinations (10/12 and 850, respectively). These values are lower than current DRLs and comparable to other international studies. Wide variations in mean doses are noted across sites. Conclusions Baseline figures for Irish CT DRLs are provided on the most frequently performed CT examinations. The variations in dose between CT departments as well as between identical scanners suggest a large potential for optimisation of examinations.     

Survey of pediatric MDCT radiation dose from university hospitals in Thailand: a preliminary for national dose survey

Background Increasing pediatric CT usage worldwide needs the optimization of CT protocol examination. Although there are previous published dose reference level (DRL) values, the local DRLs should be established to guide for clinical practice and monitor the CT radiation. Purpose To determine the multidetector CT (MDCT) radiation dose in children in three university hospitals in Thailand in four age groups using the CT dose index (CTDI) and dose length product (DLP). Material and Methods A retrospective review of CT dosimetry in pediatric patients (<15 years of age) who had undergone head, chest, and abdominal MDCT in three major university hospitals in Thailand was performed. Volume CTDI (CTDI(vol)) and DLP were recorded, categorized into four age groups: <1 year, 1-< 5 years, 5-<10 years, and 10-<15 years in each scanner. Range, mean, and third quartile values were compared with the national reference dose levels for CT in pediatric patients from the UK and Switzerland according to International Commission on Radiological Protection (ICRP) recommendation. Results Per age group, the third quartile values for brain, chest, and abdominal CTs were, respectively, in terms of CTDI(vol): 25, 30, 40, and 45 mGy; 4.5, 5.7, 10, and 15.6 mGy; 8.5, 9, 14, and 17 mGy; and in terms of DLP: 400, 570, 610, and 800 mGy cm; 80, 140, 305, and 470 mGy cm; and 190, 275, 560,765 mGy cm. Conclusion This preliminary national dose survey for pediatric CT in Thailand found that the majority of CTDI(vol) and DLP values in brain, chest, and abdominal CTs were still below the diagnostic reference levels (DRLs) from the UK and Switzerland regarding to ICRP recommendation.     

Survey of computed tomography techniques and absorbed dose in Italian hospitals: a comparison between two methods to estimate the dose–length product and the effective dose and to verify fulfilment of the diagnostic reference levels

The aim of this study was the production of the first Italian survey of radiation dose in computed tomography (CT) prior to the widespread adoption of multislice CT, in order to have a reference point to facilitate later investigation of dose exposure changes brought by this new CT modality. The collected dose data were compared with diagnostic reference levels (DRLs). The agreement between experimental dose evaluation and Monte Carlo (MC) simulations was investigated. The survey was carried out in 29 Italian hospitals, covered 48 CT scanners and 232 examinations. The dose–length product (DLP) and effective dose (E) values were estimated based on MC simulations for seven clinical protocols using the CT-Dose program. Statistical analysis showed a significant difference (p<0.01) in the DLP between the two methods, with MC values being greater than the experimental ones. For E, the MC values were greater in routine head (8.2%), cervical spine (2.7%) and lumbar spine (2.9%) studies. The weighted CT dose index, the DLP and E were always below the DRLs set by the European Community. This dose survey gives a good but incomplete picture of the Italian CT dose situation and may be useful as a reference baseline for defining clinical multislice protocols in the near future.     

单层与多层螺旋CT所致儿童受检者辐射剂量研究

目的 研究和评价儿童受检者在单层与多层螺旋CT扫描中所受到的辐射剂量。方法 测试21台CT机的头部和体部剂量指数,并结合0～1岁组、5岁组、10岁组儿童和成年人的头部和胸部常规扫描条件,计算CTDI_w、CTDI_vol、DLP值,再由DLP与有效剂量转换系数计算头部和胸部常规扫描所致各年龄组儿童和成年人的有效剂量。 结果 单位mAs的头部CTDI大于体部CTDI;在头部常规扫描中,0～1岁组、5岁组、10岁组儿童受到的有效剂量分别为2.2、1.3、1.1 mSv;在胸部常规扫描中,0～1岁组、5岁组、10岁组儿童受到的有效剂量分别为5.3、3.1、3.4 mSv;每单位mAs所致儿童有效剂量平均比成人高1.8倍;多层CT的儿童头部CTDI_vol、DLP、有效剂量值均大于单层与双层CT,多层与双层CT的儿童胸部CTDI_vol、DLP、有效剂量值均小于单层CT。 结论 与成年人相比,儿童在CT检查中可能受到更大辐射危害,应严格遵循儿童CT检查适应证,并合理选择CT扫描参数,尽可能降低儿童受到的辐射剂量。     

Image quality and dose evaluation in spiral chest CT examinations of patients with lung carcinoma

A study was undertaken to assess the quality of general chest CT examinations for indication of lung carcinoma according to the criteria proposed in the European Commission (EC) Guidelines, and to investigate their usefulness in the optimization of this practice. The criteria were evaluated for a sample of 100 examinations from five radiology departments in the Madrid area featuring single slice helical CT scanners with special emphasis on radiation dose and image quality. To determine the degree of compliance with the image criteria considered, the examinations were independently evaluated twice by five radiologists from the participating centres. A subsequent selection of the observers was made according to the consistency and independence of their readings. Dose measurements carried out in parallel supplied data to estimate the values of the CT dose indices (CTDI), dose-length product (DLP) and effective dose (E). The results show good compliance with the image criteria used - between 93% and 98% on average at the different sites, with variable degrees of internal deviation. 10 out of a total of 16 criteria proposed in the EC guidelines were met by practically all the examinations in the sample. The average weighted CTDI (CTDI(w)) values per site were in the range of 13-19 mGy; those of DLP were between 263 mGy cm and 577 mGy cm, and those of effective dose between 4 mSv and 9 mSv. The highest mean DLP value was below but close to the reference value proposed in the EC Document (650 mGy cm). In general, a weak correlation or no correlation at all was found between image quality scores and patient dose (DLP).     

Radiation doses to patients receiving computed tomography examinations in British Columbia.

OBJECTIVE: To estimate the diagnostic reference levels and effective radiation dose to patients from routine computed tomography (CT) examinations in the province of British Columbia, Canada. METHODS: The patient weight, height and computed tomography dose index or dose linear product (DLP) were recorded on study sheets for 1070 patients who were referred for clinically indicated routine CT examinations at 18 radiology departments in British Columbia. Sixteen of the scanners were multidetector row scanners. RESULTS: The average patient dose varied from hospital to hospital. The largest range was found for CT of the abdomen, for which the dose varied from 3.6 to 26.5 (average 10.1) mSv. For head CT, the range was 1.7 to 4.9 (average 2.8) mSv; for chest CT, it was 3.8 to 26 (average 9.3) mSv; for pelvis CT, it was 3.5 to 15.5 (average 9.0) mSv; and for abdomen-pelvis CT, it was 7.3 to 31.5 (average 16.3) mSv. Reference dose values were calculated for each exam. These DLP values are as follows: head, 1300 mGy cm; chest, 600 mGy cm; abdomen, 920 mGy cm; pelvis, 650 mGy cm; and abdomen-pelvis, 1100 mGy cm. CONCLUSION: Among hospitals, there was considerable variation in the DLP and patient radiation dose for a specific exam. Reference doses and patient doses were higher than those found in similar recent surveys carried out in the United Kingdom and the European Union. Patient doses were similar to those found in a recent survey in Germany.     

Dose reduction in CT while maintaining diagnostic confidence: diagnostic reference levels at routine head, chest, and abdominal CT--IAEA-coordinated research project

PURPOSE: To measure radiation doses for computed tomography (CT) of the head, chest, and abdomen and compare them with the diagnostic reference levels, as part of the International Atomic Energy Agency Research coordination project. MATERIALS AND METHODS: The local ethics committees of all participating institutions approved the study protocol. Written informed consent was obtained from all patients. All scanners were helical single-section or multi-detector row CT systems. Six hundred thirty-three patients undergoing head (n = 97), chest (n = 243), or abdominal (n = 293) CT were included. Collected data included patient height, weight, sex, and age; tube voltage and tube current-time product settings; pitch; section thickness; number of sections; weighted or volumetric CT dose index; and dose-length product (DLP). The effective dose was also estimated and served as collective dose estimation data. RESULTS: Mean volumetric CT dose index and DLP values were below the European diagnostic reference levels: 39 mGy and 544 mGy . cm, respectively, at head CT; 9.3 mGy and 348 mGy . cm, respectively, at chest CT; and 10.4 mGy and 549 mGy . cm, respectively, at abdominal CT. Estimated effective doses were 1.2, 5.9, and 8.2 mSv, respectively. CONCLUSION: Comparison of CT results with diagnostic reference levels revealed the need for revisions, partly because the newer scanners have improved technology that facilitates lower patient doses.     

Application of draft European Commission reference levels to a regional CT dose survey

A survey of CT doses in Northern Ireland in the period between October 1995 and March 1997 was carried out. The survey included all but one of the 10 scanners in use at the time, and, additionally, two others that were replacement machines. The method used was to study standard protocols and calculate doses to the NRPB mathematical phantom, so that a direct comparison could be made with other surveys carried out in a similar fashion elsewhere. The survey addressed the patient radiation dose but not image quality or clinical outcomes. It is estimated that in Northern Ireland the contribution to collective dose to the population from CT is about 40% of that from all medical X-rays. The proposed European Commission reference quantities, weighted CT dose index and dose-length product were computed and their potential use evaluated. A full study of mean values of effective dose per examination revealed the average dose per examination was not significantly different from that found in the 1989 UK survey, although several procedures gave rise to doses that were high enough to be investigated with a view to justification or reduction. One of the scanners was found to give consistently high doses. It is likely that a revision of the mAs values used on this scanner will produce a significant reduction in patient doses without compromising image quality. When compared with the draft EC reference levels, fewer procedures were found to have excessively high dose values. The proposed EC reference levels would therefore be useful for continual monitoring of CT dose status, but do not appear to provide as comprehensive an assessment of patient exposure as that given by consideration of effective doses.     

16-slice CT: achievable effective doses of common protocols in comparison with recent CT dose surveys

The aim of the study was to investigate achievable dose levels in 16-slice CT by evaluating CT dose indices (CTDI) and effective doses of dose-optimized protocols compared with 4-slice dose surveys. Normalized CTDI free in air and in 16 cm and 32 cm diameter phantoms were measured on four different 16-slice CT scanners in the Netherlands. All collimation and tube potential settings were analysed. Volume CTDI was calculated for adult protocols for brain, chest, pulmonary angiography (CTPA), abdomen and biphasic liver CT. Effective doses were calculated first using volume CTDI with conversion factors and second from CTDIair values using the ImPACT dose calculator. Average results of the 16-slice scanners were correlated to results of dose surveys with predominantly 4-slice scanners. Statistical analysis was done with Student t-tests with a Bonferroni correction; therefore p < 0.017 was significant. The results of CTDIair and weighted CTDI were documented for all scanners. Effective doses averaged over four scanners for brain, chest, CTPA, abdomen and biphasic liver protocols were 1.9+/-0.4, 3.8+/-0.4, 3.0+/-0.2, 7.2+/-0.9 and 10.2+/-1.3 mSv, respectively. Compared with dose surveys achievable effective doses were equal (p = 0.069) to significantly lower (p < 0.017) for chest and abdomen protocols. For 16-slice spiral brain CT there was a trend of equal doses compared with sequential brain CT in the dose surveys. Thus, with dose-optimized protocols 16-slice CT can achieve equal to lower effective doses in examinations of the chest and abdomen compared with 4-slice CT, while doses can remain stable in the brain.     

Population exposure to ionising radiation from CT examinations in Aosta Valley between 2001 and 2008

Recent and continuous advances in CT, such as the development of multislice CT, have promoted a rapid increase in its clinical application. Today, CT accounts for approximately 10% of the total number of medical radiographic procedures worldwide. However, the growing performance of the new CT generations have increased not only the diagnostic opportunities, but also the radiation dose to the patient. The relative contribution to the collective radiation dose is now estimated to be approximately 50%. Several papers have been published concerning the intensive use of CT and its contribution to the collective dose. However, most of the literature concerns the years 1997-2003 and the dosimetric evaluations are generally limited to the main standard protocols (chest, head and abdomen), deriving the effective dose by the simple application of the diagnostic reference levels. Only specific dosimetric analyses of single and innovative procedures have been published recently. Moreover, few data comes from Italian radiology departments. This paper aims to bridge these gaps. Firstly, it characterises in terms of measured CT dose index (CTDI) two last-generation scanners of the Radiological Department of Aosta Hospital. Secondly, it evaluates the effective dose from most of the CT examinations performed from 2001 to 2008 to compare protocols and technologies in line with the suggestions of the 2007 Recommendations of the International Commission on Radiological Protection, Publication 103. Finally, it estimates the collective dose to the population.     

Calculating effective dose on a cone beam computed tomography device: 3D Accuitomo and 3D Accuitomo FPD

OBJECTIVES: This study evaluates two methods for calculating effective dose, CT dose index (CTDI) and dose-area product (DAP) for a cone beam CT (CBCT) device: 3D Accuitomo at field size 30x40 mm and 3D Accuitomo FPD at field sizes 40x40 mm and 60x60 mm. Furthermore, the effective dose of three commonly used examinations in dental radiology was determined. METHODS: CTDI(100) measurements were performed in a CT head dose phantom with a pencil ionization chamber connected to an electrometer. The rotation centre was placed in the centre of the phantom and also, to simulate a patient examination, in the upper left cuspid region. The DAP value was determined with a plane-parallel transmission ionization chamber connected to an electrometer. A conversion factor of 0.08 mSv per Gy cm(2) was used to determine the effective dose from DAP values. Based on data from 90 patient examinations, DAP and effective dose were determined. RESULTS: CTDI(100) measurements showed an asymmetric dose distribution in the phantom when simulating a patient examination. Hence a correct value of CTDI(w) could not be calculated. The DAP value increased with higher tube current and tube voltage values. The DAP value was also proportional to the field size. The effective dose was found to be 11-77 microSv for the specific examinations. CONCLUSIONS: DAP measurement was found to be the best method for determining effective dose for the Accuitomo. Determination of specific conversion factors in dental radiology must, however, be further developed.     

Effect of multislice scanners on patient dose from routine CT examinations in East Anglia

As part of the dose optimization process, the Ionising Radiation (Medical Exposure) Regulations 2000 include requirements relating to the assessment of patient dose, and the setting and subsequent review of diagnostic reference levels. In East Anglia, audits of effective dose in CT have been carried out in 1996, 1999 and 2002. In the 2002 audit, nine of the 14 scanners assessed had been replaced since the previous audit. Eight of the new scanners were multislice scanners, acquiring up to 16 slices in a single rotation. The objective of the 2002 audit was to investigate the effect of the introduction of these multislice scanners on patient doses from routine CT examinations. Exposure parameters were collected for 10 different types of routine CT examination. In excess of 550 sets of patient data were obtained. For each of these, effective doses were calculated using the results of Monte Carlo simulations published by the National Radiological Protection Board. Averaged across all 10 examinations, regional mean effective doses are 34% higher than in 1999. The multislice scanners in the region give, on average, 35% more effective dose than the single-slice scanners. The effect of collimation in multislice scanners makes these effective dose differences most notable for examinations that use narrow slice widths. Further optimization of exposures on multislice scanners has the potential to reduce the differences observed between single-slice and multislice doses. However, when taken in combination with the increased use of CT in many hospitals, the effective dose increases observed are likely to result in a significant increase in the already substantial collective radiation dose from CT.     

Estimation of exposure dose on MDCT examination--the measurement of organ dose and effective dose by anthropomorphic phantom

In order to evaluate the exposure dose in CT examinations, we measured the tissue and organ doses by test site in 4-row, 16-row, and 64-row multi detector CT by using an anthropomorphic phantom and fluorescent glass dosimeters. Furthermore, we calculated the effective dose by using the tissue weighting factor recommended by the ICRP in 2007. The effective dose in the head and neck examinations was 1.4-3.1 mSv, whereas the maximum skin dose was 278.9 mGy in head perfusion CT. The effective dose in examinations of the body trunk was 10.1-35.2 mSv. In addition, the organ dose and skin dose in the scanning range was similar to the CTDI(vol) in head and neck examinations, while it was higher than the CTDI(vol) in examinations of the body trunk. The exposure dose of patients undergoing CT is high in comparison to other radiological examinations. As a result, due to consecutive examinations, an absorbed dose of more than 100 mGy is possible. A future problem therefore remains how to lower the overall exposure dose with the introduction of new radiographic diagnostic modalities, such as phase scan or coronary CT angiography.     

Multi-detector row CT: radiation dose characteristics

PURPOSE: To determine the dose characteristics of multi-detector row computed tomography (CT) and to provide tabulated dose values and rules of thumb that assist in minimizing the radiation dose at multi-detector row CT. MATERIALS AND METHODS: Weighted CT dose index (CTDI100w) values were obtained from three multi-detector row CT scanners (LightSpeed; GE Medical Systems, Milwaukee, Wis) for both head and body CT modes by using standard CT-dose phantoms. The CTDI100w was determined as a function of x-ray tube voltage (80, 100, 120, 140 kVp), tube current (range, 50-380 mA), tube rotation time (0.5-4.0 seconds), radiation profile width (RPW) (5, 10, 15, 20 mm), and acquisition mode (helical high-quality and high-speed modes and axial one-, two-, and four-section modes). Statistical regression was performed to characterize the relationships between CTDI100w and various technique factors. RESULTS: The CTDI100w (milligray) increased linearly with tube current: in head mode, CTDI100w = (0.391 mGy/mA +/- 0.004) x tube current (milliampere) (r2 = 0.999); in body mode, CTDI100w = (0.162 mGy/mA +/- 0.002) x tube current (milliampere) (r2 = 0.999). The CTDI100w increased linearly with rotation time: in head mode, CTDI100w = (34.7 mGy/sec +/- 0.2) x rotation time (seconds) (r2 = 1.0); in body mode, CTDI100w = (13.957 mGy/sec +/- 0.005) x rotation time (seconds) (r2 = 1.0). The relationship of normalized CTDI100w (milligrays per 100 mAs) with tube voltage followed a power law: in head mode, CTDI100w = (0.00016 mGy/100 mAs. kVp +/- 0.00007) x (tube voltage)(2.5+/-0.1) (r2 = 0.997); in body mode, CTDI100w = (0.000012 mGy/100 mAs. kVp +/- 0.000007) x (tube voltage)(2.8+/-0.1) (r2 = 0.996). In all scanning modes, CTDI100w decreased when RPW increased. CTDI100w was 10% higher in head mode and 13% lower in body mode compared with the value suggested by the manufacturer, which is displayed at the scanner console. When deposited power exceeded 24 kW, CTDI100w increased by 10% as a result of use of the large focal spot. CONCLUSION: The authors provide a set of tables of radiation dose as a function of imaging protocol to facilitate implementation of radiation dose-efficient studies.     

Variation of patient dose in head CT.

CT dose varies with both equipment related and operator dependent factors. Thermoluminescence dosimetry (TLD) was employed in two phantoms to investigate the variation in absorbed dose for head CT scans, using a cylindrical head CT dose phantom. Dose profiles were plotted and the computed tomography dose index (CTDI) calculated for a single 10 mm thick slice on 14 CT scanners. An anthropomorphic head phantom was also scanned from the base-of-skull to the vertex using 10/10 mm slices. The absorbed dose measured at the centre of the scan series is reported (Dmid). The mean CTDIw for the 14 scanners was 60.0 mGy, while the mean Dmid was 45.8 mGy. Dmid better represents the absorbed dose in human tissues. The CTDIw and Dmid normalized to mAs varied by up to a factor of 2.2 for the different scanners. Equipment related factors contribute to such variations. However, variations due to operator dependent factors such as the choice of exposure factors, scanning protocol and positioning technique must also be considered. When such factors are taken into account the absorbed dose received by the patient can vary considerably, by as much as 16.2 for lens dose. Increased awareness of the factors influencing CT dose and the standardization of scanning protocols is recommended.     

河南省CT检查所致受检者剂量调查与分析

目的研究河南省CT检查所致儿童和成人受检者的剂量水平,探讨其影响因素,为制定我国和地区CT诊断参考(指导)水平提供基础资料。方法采用分层配额抽样方法选取河南省7个地市31台CT共计1113例受检者主要检查类型进行剂量调查,调查内容包括受检者和设备基本信息、扫描参数、相关剂量学信息等,通过剂量转换系数估算其所致典型有效剂量。结果头部常规CT扫描中,0~1岁、>1~5岁、>5~10岁、>10~15岁组儿童CTDIw的75%分位值分别为32.2、37.2、43.0、46.7 mGy,DLP的75%分位值分别为478.0、572.0、715.6、743.9 mGy·cm,有效剂量分别为5.26、3.83、2.86、2.38 mSv;在胸部常规扫描中,0~1岁、>1~5岁、>5~10岁、>10~15岁组儿童CTDIw的75%分位值均为9.3 mGy,DLP的75%分位值分别为141.7、178.8、224.0、238.7 mGy·cm,有效剂量分别为5.53、4.64、4.03、3.10 mSv。CT检查所致成人受检者头部、胸部、腹部CTDIw的75%分位值分别为57.4、16.2、19.4 mGy,DLP的75%分位值分别为818.3、504.7和571.1 mGy·cm,有效剂量分别为1.72、7.07和8.57 mSv。结论随着河南省CT设备的更新,检查技术的日益进步以及CT应用频度的快速增长,医疗机构应恰当选取CT各类检查的扫描参数,加强其影像质量及其所致剂量的优化匹配研究,完善CT诊断参考(指导)水平,尤其是对射线敏感的儿童应尽快建立诊断参考(指导)水平,推动CT检查医疗照射防护最优化。