CTDI Values Research Articles

Assessment of volumetric absorbed dose for mobile fluoroscopic 3D image acquisition.

Mobile fluoroscopy (c‐arm) units offering 3D image reconstruction are becoming more common in surgical settings. Although these images are “CT‐like” and sometimes replace the postoperative CT, the acquisition is technically very different from a traditional CT acquisition. Dose assessment is complicated by a large beam width, automatic exposure rate control, and a rotation of less than 360°. The purpose of this work was to explore the impact of these factors on the volumetric dose calculation and to provide practical recommendations for clinical physicists assessing dose from these units using commonly available equipment. CTDIW was calculated using the IAEA method for dosimetry of wide beams and compared to scans of the 32‐cm CTDI phantom using the full beam width and a 20‐mm collimated beam width. The impact of the partial rotation on the CTDIW calculation was assessed by acquiring measurements at four and twelve positions on the phantom periphery. For the system tested, the CTDIW was calculated to be 16.1 mGy using the IAEA method with default clinical protocol. Results showed that measuring CTDIW with the full beam width or a collimated beam width alone resulted in CTDI values of 19.0 mGy and 19.5 mGy, respectively. Using four peripheral measurements instead of 12 resulted in a difference of 4% for a collimated beam and 6% for an open beam. Variations in positioning on the order of a few centimeters resulted in a variation of only 4% with an open beam. The excellent reproducibility of the measurements using the full beam width suggests that this simple method is adequate for year‐to‐year comparisons. In contrast, the IAEA method is difficult to employ, particularly with 180° acquisitions. Use of peripheral measurements in excess of the usual four is time‐consuming and not necessary for most applications obtained with the geometry specific to this system.

Comparison of Measured Values of CTDI and DPL with Standard Reference values of Different CT Scanners for dose Management

The study is based on estimate of CTDI and DLP values for patients' dose optimization procedures. Technical parameters were obtained for three groups of randomly selected patients undergoing abdominal CT examinations of 320 patients of age 20-80 years. The measured values were obtained on image data and the standard reference values of various machines were obtained from service manual as part of QC/QA and the recommended values from ICRP publication 103. The mean CTDI and DLP parameters were; 6.33mGy and 936.25mGy respectively. Furthermore, the mean recorded values of CTDIVOL values were well within ICRP recommendation when the protocol was completed in one scan. On the other hand, in the case of multiscan the total CTDIVol was higher than the ICRP recommendations. While the mean DLP values were higher than the recommended value of 780 mGy-cm by ICRP publication 103. Finally, approximately 37% of the total varied CTDI and DLP values were higher than the recommended dose by ICRP publication 103.

Radiation Dose Reduction in MDCT through Tube Current Optimization of Pre-Contrast Media on CT Brain Angiography Subtraction Technique

Background/Objectives: The purpose of this study was to reduce of radiation dose through optimizing the tube current exposed pre-contrast media in multi-detector computed tomography (MDCT) brain angiography subtraction technique (BAST). Methods/Statistical Analysis: The tube voltage were fixed and the tube current was set to 100 vs 70 mAs, 100 vs 50 mAs and 100 vs 30 mAs for the two respective inspections performed pre-contrast media. The average diameters of the posterior cerebral artery, the anterior cerebral artery and the basilar artery were measured to verify the statistical difference on 30 patients. In addition, the radiation dose in the tube current is measured. Findings: When the tube current was set adjusted from 100 mAs to 30 mAs, the average diameters of the left/right posterior cerebral artery, the left/right anterior cerebral artery and the basilar artery indicated no significant difference. And the result of measured weighted CTDI values are 8.9 mGy in 100 mAs, 6.24 mGy in 70 mAs, 4.71 mGy in 50 mAs, 2.63 mGy in 30 mAs and could be reduced up to 70.5%. This study is limited in that it was conducted based on a small experimental group to minimize the number of people being exposed to radiation. However, as a result of continuously applying the experiment results to the current clinical environment, there has been no request for a re-inspection due to the low radiation dose. Improvements/Applications: The use of subtraction technique is expected to decrease the exposure dose while operating CT brain angiography on patients and actualize the safe CT brain angiography

TU‐H‐207A‐02: Relative Importance of the Various Factors Influencing the Accuracy of Monte Carlo Simulated CT Dose Index

Purpose:Monte Carlo simulation is a frequently used technique for assessing patient dose in CT. The accuracy of a Monte Carlo program is often validated using the standard CT dose index (CTDI) phantoms by comparing simulated and measured CTDI100. To achieve good agreement, many input parameters in the simulation (e.g., energy spectrum and effective beam width) need to be determined. However, not all the parameters have equal importance. Our aim was to assess the relative importance of the various factors that influence the accuracy of simulated CTDI100.Methods:A Monte Carlo program previously validated for a clinical CT system was used to simulate CTDI100. For the standard CTDI phantoms (32 and 16 cm in diameter), CTDI100 values from central and four peripheral locations at 70 and 120 kVp were first simulated using a set of reference input parameter values (treated as the truth). To emulate the situation in which the input parameter values used by the researcher may deviate from the truth, additional simulations were performed in which intentional errors were introduced into the input parameters, the effects of which on simulated CTDI100 were analyzed.Results:At 38.4‐mm collimation, errors in effective beam width up to 5.0 mm showed negligible effects on simulated CTDI100 (<1.0%). Likewise, errors in acrylic density of up to 0.01 g/cm3 resulted in small CTDI100 errors (<2.5%). In contrast, errors in spectral HVL produced more significant effects: slight deviations (±0.2 mm Al) produced errors up to 4.4%, whereas more extreme deviations (±1.4 mm Al) produced errors as high as 25.9%. Lastly, ignoring the CT table introduced errors up to 13.9%.Conclusion:Monte Carlo simulated CTDI100 is insensitive to errors in effective beam width and acrylic density. However, they are sensitive to errors in spectral HVL. To obtain accurate results, the CT table should not be ignored.This work was supported by a Faculty Research and Development Award from Cleveland State University.

SU‐G‐206‐03: CTDI Per KV at Phantom Center and Periphery: Comparison Between Major CT Manufacturers

Purpose:The purpose of this study was to: 1) compare scanners output by measuring normalized CTDIw (mGy/100mAs) in different CT makes and models and at different kV's, and 2) quantify the relationship between kV and CTDI and compare this relationship between the different manufacturers.Methods:Study included forty scanners of major CT manufacturers and of various models. Exposure was measured at center and 12 o'clock holes of head and body CTDI phantoms, at all available kV's, and with the largest or second largest available collimation in each scanner. Average measured CTDI's from each CT manufacturer were also plotted against kV and the fitting equation: CTDIw (normalized) = a.kVb was calculated. The power (b) value may be considered as an indicator of spectral filtration, which affects the degree of beam hardening. Also, HVLs were measured at several scanners.Results:Results showed GE scanners, on average, had higher normalized CTDIw than those of Siemens and Philips, in both phantom sizes and at all kV's. ANOVA statistic indicated the difference was statistically significant (p < 0.05). Comparison between Philips and Siemens, however, was not statistically significant. Curve fitting showed b values ranged from 2.4 to 2.9 (for Head periphery and center, respectively); and was about 2.8 for Body phantom periphery, and 3.2 at the center of Body phantom. Fitting equations (kV vs. CTDI) will be presented and discussed. GE's CTDIw vs. HVL showed very strong correlation (r > 0.99).Conclusion:Partial characterization of scanners output was performed which may be helpful in dose estimation to internal organs. The relatively higher output from GE scanners may be attributed to lower filtration. Work is still in progress to obtain CTDI values from other scanners as well as to measure their HVLs.

Analisis Perubahan kV dan mAs terhadap Kualitas Gambar dan Dosis Radiasi pada Pemeriksaan Multislice Computed Tomography Abdomen dalam Kasus Tumor Abdomen di Instalasi Radiologi RSUD dr. Saiful Anwar Malang

Backgroud: Examination of the abdomen CT scan is often done by using standard protocol, meanwhile the actual parameter can be modified according to local needs considering image quality and radiation dose based on Karabulut and Ariyuek (2016). Abdomen CT Scan by GE 16 slices unit in Radiology Instaallation of Dr. Saiful Anwar Malang Hospital, using exposure factor of 120 kV, 234 mAs and the value of the CTDI dose was 53.04 mGy. While the BAPETEN’s reference of CTDI value, a CT scan of abdomen was 25 mGy. This study aims to determine the changes of the value of kV and mAs to the image quality and the radiaton dose in the abdomen MSCT examination on abdominal tumor case in Radiology Installation of Dr. Saiful Anwar Malang Hospital.Methods: This research was a quantitative research with an experimental approach. The data were collected from three variations of tube voltage (kV) ie 100 kV, 120 kV and 140 kV and three variations of tube current value and time (mAs) ie, 180 mAs, 195 mAs, and 210 mAs. Radiographs was evaluated by three radiology physicians. Data were analyzed by scoring method of respondent’s assessment to assess MSCT image quality of abdominal tumor, while the radiation dose was obtained by CTDI recording.Results: The results showed that there was influence of tube voltage variation to image quality of abdominal tumor using MSCT unit. The higher kV used, the higher image quality resulted. From the calculation of the percentage from the assessment, the highest score of variation was at 140 kV, while the lowest score of variation was at 100 kV. Based on the recording CTDI radiation dose on the monitor, found that the higher value of kV, the higher radiation resulted. The mAs variations influenced the image quality of abdominal tumor using MSCT unit. Acoording to the percentage of the assessment, the highest score of variation found in 210 mAs, and the lowest score of variation found in 180 mAs. Based on the recording of radiation dose on the monitor, the higher mAs value, the higher radiation dose using MSCT unit. It was recommended to use 195 kV and 120 mAs for MSCT examination of abdominal tumor in Radiology Installation of Dr. Saiful Anwar Malang Hospital.Conclusion: There was influence of kV and mAs variation to anatomical image clarity and radiation dose of abdomen MSCT examination

Survey of volume CT dose index in Japan in 2014.

The aims of this study are to propose a new set of Japanese diagnostic reference levels (DRLs) for 2014 and to study the impact of tube voltage and the type of reconstruction algorithm on patient doses. The volume CT dose index (CTDI(vol)) for adult and paediatric patients is assessed and compared with the results of a 2011 national survey and data from other countries. Scanning procedures for the head (non-helical and helical), chest and upper abdomen were examined for adults and 5-year-old children. A questionnaire concerning the following items was sent to 3000 facilities: tube voltage, use of reconstruction algorithms and displayed CTDI(vol). The mean CTDI(vol) values for paediatric examinations using voltages ranging from 80 to 100 kV were significantly lower than those for paediatric examinations using 120 kV. For adult examinations, the use of iterative reconstruction algorithms significantly reduced the mean CTDI(vol) values compared with the use of filtered back projection. Paediatric chest and abdominal scans showed slightly higher mean CTDI(vol) values in 2014 than in 2011. The proposed DRLs for adult head and abdominal scans were higher than those reported in other countries. The results imply that further optimization of CT examination protocols is required for adult head and abdominal scans as well as paediatric chest and abdominal scans. Low-tube-voltage CT may be useful for reducing radiation doses in paediatric patients. The mean CTDI(vol) values for paediatric scans showed little difference that could be attributed to the choice of reconstruction algorithm.

TU‐E‐201‐00: Eye Lens Dosimetry for Patients and Staff

TU‐E‐201‐00: Eye Lens Dosimetry for Patients and Staff

TU‐E‐201‐01: Methods for Eye Lens Dosimetry and Studies On Lens Opacities with Interventionists

TU‐E‐201‐01: Methods for Eye Lens Dosimetry and Studies On Lens Opacities with Interventionists

TU‐E‐201‐03: Eye Lens Dosimetry in Radiotherapy Using Contact Lens‐Shaped Applicator

TU‐E‐201‐03: Eye Lens Dosimetry in Radiotherapy Using Contact Lens‐Shaped Applicator

TU‐E‐201‐02: Eye Lens Dosimetry From CT Perfusion Studies

TU‐E‐201‐02: Eye Lens Dosimetry From CT Perfusion Studies

TU‐G‐204‐04: A Unified Strategy for Bi‐Factorial Optimization of Radiation Dose and Contrast Dose in CT Imaging

Purpose:To substantiate the interdependency of contrast dose, radiation dose, and image quality in CT towards the patient‐ specific optimization of the imaging protocolsMethods:The study deployed two phantom platforms. A variable sized (12, 18, 23, 30, 37 cm) phantom (Mercury‐3.0) containing an iodinated insert (8.5 mgI/ml) was imaged on a representative CT scanner at multiple CTDI values (0.7–22.6 mGy). The contrast and noise were measured from the reconstructed images for each phantom diameter. Linearly related to iodine‐concentration, contrast‐to‐noise ratio (CNR), were calculated for 16 iodine‐concentration levels (0–8.5 mgI/ml). The analysis was extended to a recently developed suit of 58 virtual human models (5D XCAT) with added contrast dynamics. Emulating a contrast‐enhanced abdominal image procedure and targeting a peak‐enhancement in aorta, each XCAT phantom was “imaged” using a simulation platform (CatSim, GE). 3D surfaces for each patient/size established the relationship between iodine‐concentration, dose, and CNR. The ratios of change in iodine‐concentration versus dose (IDR) to yield a constant change in CNR were calculated for each patient size.Results:Mercury phantom results show the image‐quality size‐ dependence on CTDI and IC levels. For desired image‐quality values, the iso‐contour‐lines reflect the trade off between contrast‐material and radiation doses. For a fixed iodine‐concentration (4 mgI/mL), the IDR values for low (1.4 mGy) and high (11.5 mGy) dose levels were 1.02, 1.07, 1.19, 1.65, 1.54, and 3.14, 3.12, 3.52, 3.76, 4.06, respectively across five sizes. The simulation data from XCAT models confirmed the empirical results from Mercury phantom.Conclusion:The iodine‐concentration, image quality, and radiation dose are interdependent. The understanding of the relationships between iodine‐concentration, image quality, and radiation dose will allow for a more comprehensive optimization of CT imaging devices and techniques, providing the methodology to balance iodine‐concentration and dose based on patient's attributes.

Development and validation of a GEANT4 radiation transport code for CT dosimetry.

The authors have created a radiation transport code using the GEANT4 Monte Carlo toolkit to simulate pediatric patients undergoing CT examinations. The focus of this paper is to validate their simulation with real-world physical dosimetry measurements using two independent techniques. Exposure measurements were made with a standard 100-mm CT pencil ionization chamber, and absorbed doses were also measured using optically stimulated luminescent (OSL) dosimeters. Measurements were made in air with a standard 16-cm acrylic head phantom and with a standard 32-cm acrylic body phantom. Physical dose measurements determined from the ionization chamber in air for 100 and 120 kVp beam energies were used to derive photon-fluence calibration factors. Both ion chamber and OSL measurement results provide useful comparisons in the validation of the Monte Carlo simulations. It was found that simulated and measured CTDI values were within an overall average of 6% of each other.

Multi-national findings on radiation protection of children.

This article reviews issues of radiation protection in children in 52 low-resource countries. Extensive information was obtained through a survey by the International Atomic Energy Agency (IAEA); wide-ranging information was available from 40 countries and data from the other countries pertained to frequency of pediatric CT examinations. Of note is that multi-detector CT (MDCT) was available in 77% of responses to the survey, typically nodal centers in these countries. Nearly 75% of these scanners were reported to have dose displays. The pediatric CT usage was lower in European facilities as compared to Asian and African facilities, where usage was twice as high. The most frequently scanned body part was the head. Frequent use of 120 kVp was reported in children. The ratio of maximum to minimum CT dose index volume (CTDIvol) values varied between 15 for abdomen CT in the age group 5-10 years and 100 for chest CT in the age group <1 year. In 8% of the CT systems, CTDI values for pediatric patients were higher than those for adults in at least one age group and for one type of examination. Use of adult protocols for children was associated with CTDIw or CTDIvol values in children that were double those of adults for head and chest examination and 50% higher for abdomen examination. Patient dose records were kept in nearly half of the facilities, with the highest frequency in Europe (55% of participating facilities), and in 49% of Asian, 36% of Latin American and 14% of African facilities. The analysis of the first-choice examinations in seven clinical conditions showed that practice was in accordance with guidelines for only three of seven specified clinical conditions.

SU‐E‐I‐19: CTDI Values for All Protocols: Using the Ratio of the DLP Measured in CTDI Phantoms to the Measured Air Exposure

Purpose:To propose a method other than CTDI phantom measurements for routine CT dosimetry QA. This consists of taking a series of air exposure measurements and calculating a factor for converting from this exposure measurement to the protocol's associated head or body CTDI value using DLP. The data presented are the ratios of phantom DLP to air exposure ratios for different scanners, as well as error in the displayed CTDI.Methods:For each scanner, the CTDI is measured at all available tube voltages using both the head and body phantoms. Then, the exposure is measured using a pencil chamber in air at isocenter. A ratio of phantom DLP to exposure in air for a given protocol may be calculated and used for converting a simple air dose measurement to a head or body CTDI value. For our routine QA, the exposure in air for different collimations, mAs, and kVp is measured, and displayed CTDI is recorded. Therefore, the ratio calculated may convert these exposures to CTDI values that may then be compared to the displayed CTDI for a large range of acquisition parameter combinations.Results:It was found that all scanners tend to have a ratio factor that slightly increases with kVp. Also, Philips scanners appear to have less of a dependence on kVp; whereas, GE scanners have a lower ratio at lower kVp. The use of air exposure times the DLP conversion yielded CTDI values that were less than 10% different from the displayed CTDI on several scanners.Conclusion:This method may be used as a primary method for CT dosimetry QA. As a result of the ease of measurement, a dosimetry metric specific to that scanner may be calculated for a wide variety of CT protocols, which could also be used to monitor display CTDI value accuracy.

SU‐F‐18C‐09: Assessment of OSL Dosimeter Technology in the Validation of a Monte Carlo Radiation Transport Code for CT Dosimetry

Purpose:To assess the utility of optically stimulated luminescent (OSL) dosimeter technology in calibrating and validating a Monte Carlo radiation transport code for computed tomography (CT).Methods:Exposure data were taken using both a standard CT 100‐mm pencil ionization chamber and a series of 150‐mm OSL CT dosimeters. Measurements were made at system isocenter in air as well as in standard 16‐cm (head) and 32‐cm (body) CTDI phantoms at isocenter and at the 12 o' clock positions. Scans were performed on a Philips Brilliance 64 CT scanner for 100 and 120 kVp at 300 mAs with a nominal beam width of 40 mm. A radiation transport code to simulate the CT scanner conditions was developed using the GEANT4 physics toolkit. The imaging geometry and associated parameters were simulated for each ionization chamber and phantom combination. Simulated absorbed doses were compared to both CTDI100 values determined from the ion chamber and to CTDI100 values reported from the OSLs. The dose profiles from each simulation were also compared to the physical OSL dose profiles.Results:CTDI100 values reported by the ion chamber and OSLs are generally in good agreement (average percent difference of 9%), and provide a suitable way to calibrate doses obtained from simulation to real absorbed doses. Simulated and real CTDI100 values agree to within 10% or less, and the simulated dose profiles also predict the physical profiles reported by the OSLs.Conclusion:Ionization chambers are generally considered the standard for absolute dose measurements. However, OSL dosimeters may also serve as a useful tool with the significant benefit of also assessing the radiation dose profile. This may offer an advantage to those developing simulations for assessing radiation dosimetry such as verification of spatial dose distribution and beam width.

SU‐E‐I‐18: CT Scanner QA Using Normalized CTDI Ratio

Purpose:To create a ratio of weighted computed tomography dose index (CTDIw) data normalized to in‐air measurements (CTDIair) as a function of beam quality to create a look‐up table for frequent, rapid quality assurance (QA) checks of CTDI.Methods:The CTDIw values were measured according to TG‐63 protocol using a pencil ionization chamber (Unfors Xi CT detector) and head and body Polymethyl methacrylate (PMMA) phantoms (16 and 32 cm diameter, respectively). Single scan dose profiles were measured at each clinically available energy (80,100,120,140 kVp) on three different CT scanners (two Siemens SOMATOM Definition Flash and one GE Optima), using a tube current of 400 mA, a one second rotation time, and the widest available beam width (32 × 0.6 mm and 16 × 1.25 mm, respectively). These values were normalized to CTDIair measurements using the same conditions as CTDIw. The ratios (expressed in cGy/R) were assessed for each scanner as a function of each energy's half value layer (HVL) paired with the phantom's appropriate bow tie filter measured in mmAl.Results:Normalized CTDI values vary linearly with HVL for both the head and body phantoms. The ratios for the two Siemens machines are very similar at each energy. Compared to the GE scanner, these values vary between 10–20% for each kVp setting. Differences in CTDIair contribute most to the deviation of the ratios across machines. Ratios are independent of both mAs and collimation.Conclusion:Look‐up tables constructed of normalized CTDI values as a function of HVL can be used to derive CTDIw data from only three in‐air measurements (one for CTDIair and two with added filtration for HVL) to allow for simple, frequent QA checks without CT phantom setup. Future investigations will involve comparing results with Monte Carlo simulations for validation.

SU‐E‐I‐91: Reproducibility in Prescribed Dose in AEC CT Scans Due to Table Height, Patient Size, and Localizer Acquisition Order

Purpose:In CT scanners, the automatic exposure control (AEC) tube current prescription depends on the acquired prescan localizer image(s). The purpose of this study was to quantify the effect that table height, patient size, and localizer acquisition order may have on the reproducibility in prescribed dose.Methods:Three phantoms were used for this study: the Mercury Phantom (comprises three tapered and four uniform regions of polyethylene 16, 23, 30, and 37 cm in diameter), acrylic sheets, and an adult anthropomorphic phantom. Phantoms were positioned per clinical protocol by our chief CT technologist or broader symmetry. Using a GE Discovery CT750HD scanner, a lateral (LAT) and posterior‐anterior (PA) localizer was acquired for each phantom at different table heights. AEC scan acquisitions were prescribed for each combination of phantom, localizer orientation, and table height; the displayed volume CTDI was recorded for each. Results were analyzed versus table height.Results:For the two largest Mercury Phantom section scans based on the PA localizer, the percent change in volume CTDI from ideal were at least 20% lower and 35% greater for table heights 4 cm above and 4 cm below proper centering, respectively. For scans based on the LAT localizer, the percent change in volume CTDI from ideal were no greater than 12% different for 4 cm differences in table height. The properly centered PA and LAT localizer‐based volume CTDI values were within 13% of each other.Conclusion:Since uncertainty in vertical patient positioning is inherently greater than lateral positioning and because the variability in dose exceeds any dose penalties incurred, the LAT localizer should be used to precisely and reproducibly deliver the intended amount of radiation prescribed by CT protocols. CT protocols can be adjusted to minimize the expected change in average patient dose.

Database of normalised computed tomography dose index for retrospective CT dosimetry

Volumetric computed tomography dose index (CTDIvol) is an important dose descriptor to reconstruct organ doses for patients combined with the organ dose calculated from computational human phantoms coupled with Monte Carlo transport techniques. CTDIvol can be derived from weighted CTDI (CTDIw) normalised to the tube current–time product (mGy/100 mAs), using knowledge of tube current–time product (mAs), tube potential (kVp), type of CTDI phantoms (head or body), and pitch. The normalised CTDIw is one of the characteristics of a CT scanner but not readily available from the literature. In the current study, we established a comprehensive database of normalised CTDIw values based on multiple data sources: the ImPACT dose survey from the United Kingdom, the CT-Expo dose calculation program, and surveys performed by the US Food and Drug Administration (FDA) and the National Lung Screening Trial (NLST). From the sources, the CTDIw values for a total of 68, 138, 30, and 13 scanner model groups were collected, respectively. The different scanner groups from the four data sources were sorted and merged into 162 scanner groups for eight manufacturers including General Electric (GE), Siemens, Philips, Toshiba, Elscint, Picker, Shimadzu, and Hitachi. To fill in missing CTDI values, a method based on exponential regression analysis was developed based on the existing data. Once the database was completed, two different analyses of data variability were performed. First, we averaged CTDI values for each scanner in the different data sources and analysed the variability of the average CTDI values across the different scanner models within a given manufacturer. Among the four major manufacturers, Toshiba and Philips showed the greatest coefficient of variation (COV) (=standard deviation/mean) for the head and body normalised CTDIw values, 39% and 54%, respectively. Second, the variation across the different data sources was analysed for CT scanners where more than two data sources were involved. The CTDI values for the scanners from Siemens showed the greatest variation across the data sources, being about four times greater than the variation of Toshiba scanners. The established CTDI database will be used for the reconstruction of CTDIvol and then the estimation of individualised organ doses for retrospective patient cohorts in epidemiologic studies.

Radiation exposure during paediatric emergency CT: Time we took notice?

IntroductionConcerns exist about radiation exposure during medical imaging. Comprehensive computerised tomography (CT) dose standards exist for adults, but are incomplete for children. We investigated paediatric CT radiation doses at a NHS Trust in order to define the extent of the risk. MethodsCT dose indicators (CTDI) were recorded for all scans on paediatric patients from January – December 2011 and benchmarked against American College of Radiologists reference levels (75mGy for adult head, 25mGy for adult abdomen, and 20mGy for paediatric (5-year-old) abdomen). Size-specific dose estimates (SSDE) were calculated based on effective patient diameter as recommended by the American Association of Physicists in Medicine. Student t-test was used to compare CTDI and SSDE values for each anatomical region. ResultsOf 53,648 paediatric emergency presentations, CT was requested in 211 (0.39%). One hundred fifty-four patients underwent 169 scans, with the rest being cancelled for clinical improvement or senior overrule. Indication for CT was trauma in 130/154 (90%), of which 55% were after falls, 19% following road traffic collisions, 12% after sporting injury, and 12% after alleged assault. CTDI values were available for 96/169 (57%) scans, with the rest lacking sufficient data. There was no significant difference between CTDI and derived SSDE values. 3% of head scans exceeded the adult head reference level. ConclusionThere is wide variation in radiation exposure during paediatric trauma CT, with some scans delivering doses in excess of recommended adult values. There is an urgent need to define standards for radiation dose in paediatric CT for all ages and anatomical regions.