Radiation dose in computed tomography of the heart.

Estimates of individual patient risk, and epidemiologic studies assessing potential late effects, must use patient size–specific dose estimates—they cannot use only scanner output (volume CT dose index or dose-length product).

Practical Strategies to Reduce Pediatric CT Radiation Dose

Computed tomography (CT) has been a boon for medical care. By generating detailed anatomical pictures, the technology can improve diagnoses, limit unneeded medical procedures, and enhance treatment. However, CT scans also dose patients with ionizing radiation, a known human carcinogen, posing a potential downside for public health. Mounting health worries over radiation risks are now driving efforts to limit avoidable CT scans and to reduce radiation doses where possible. “There’s a national focus on this issue right now,” says Marilyn Goske, a professor of radiology at Cincinnati Children’s Hospital Medical Center and chairwoman of the Image Gently campaign, a pediatric education and awareness campaign from the Alliance for Radiation Safety in Pediatric Imaging. In December 2011 the Institute of Medicine (IOM) published a report concluding that ionizing radiation contributes more to the development of breast cancer than any other type of routine environmental exposure.1 About half the U.S. annual exposure to ionizing radiation comes from natural sources, including cosmic rays, but most of the rest comes from medical imaging and from CT scans in particular.1 The IOM cited research by Amy Berrington de Gonzalez, a senior investigator in the Radiation Epidemiology Branch of the National Cancer Institute (NCI), whose calculations suggest that the CT scans performed in the United States in 2007 might produce up to 29,000 cancers in the future, about 6% of them in the breast and the remainder in the lungs, brain, and other organs.2 But the spotlight on CT safety has also drawn a backlash from those who say the risks are overblown. On 13 December 2011 the American Association of Physicists in Medicine (AAPM) issued a statement claiming that risks from CT imaging are “too low to be detectible and may be non-existent.”3 The AAPM added that “speculative predictions about cancer incidence and death” should be discouraged because they generate sensationalist media coverage that deters some patients who need CT scans from having them. Donald Miller, acting chief of the Diagnostic Devices Branch of the U.S. Food and Drug Administration (FDA) Center for Devices and Radiological Health, cites 2 basic principles for decreasing CT radiation risks. One is justification, which refers to prescribing a CT exam only when it is medically necessary. The other is optimization, which refers to adjusting and operating a CT scanner so that images adequate for diagnosis are obtained at the lowest possible dose. Justification is more difficult to address, Miller says, because it involves case-by-case decisions made by individual clinicians. More attention has been paid to optimization, he says, but both principles are equally important.

The doses received by the patient during Computed Tomography (CT) examination are relatively significant compared with the doses received by patients undergoing classic X-ray examinations. Owing to this, each country should adopt a consistent policy to optimize the doses delivered to the patient during CT examination. One of the available options for the dose optimization is the implementation of the Diagnostic Reference Levels (DRLs) to evaluate thedose delivered to the patient and to guide the operators for the choice of parameters during CT examinations. Actually, Madagascar hasn’t got yet his own DRLs, so that the International Atomic Energy Agency (IAEA) or other international existing DRLs are used to fill this gap. The present study was performed to analyze the feasibility of setting (DRLs) atnational level. The study is a part of an IAEA Project entitled “Strengthening Technical Capabilities for Patient and Occupational Radiation Protection in Member States”, RAF9053. For this purpose, three public and private hospitals using computed tomography were selected. The patient dose assessment was performed by determining the Computed Tomography Dose Index (CTDI), Multiple Scan Average Dose (MSAD), Dose Length Product (DLP) and Effective dose (E) for an adult chest and skull CT examination. Pencil ionization chamber was used, having an active length of 100 mm, connected with an electrometer (RAD-CHECK). The system was calibrated through the Secondary Standard Dosimetry Laboratory of Madagascar (SSDL-Madagascar) before the measurements campaign. To simulate the patient presence, two types of Polymethylmethacrylate (PMMA) phantoms were used. The first, having 32 cm diameter was used to replace an adult body patient, and the second phantom, having 16 cm diameter simulate the head of an adult patient. The results were compared with the International Diagnostic Reference Level which is chosen for this study. It has beenestablished that the obtained values are similar to the existing DRLs. Measurements performed during this study can be useful for the patient dose optimization and considered as the first and main step for the National Diagnostic Reference Level setting for Computed Tomography in Madagascar.

Automatic radiation dose monitoring for CT of trauma patients with different protocols: feasibility and accuracy

This article describes basic radiation dose concepts as well as those specifically developed to describe the radiation dose from computed tomography (CT). Basic concepts of radiation dose are reviewed, including exposure, absorbed dose, and effective dose. Radiation dose from CT demonstrates variations within the scan plane and along the z axis because of its unique geometry and usage. Several CT-specific dose descriptors have been developed: the Multiple Scan Average Dose descriptor, the Computed Tomography Dose Index (CTDI) and its variations (CTDI(100), CTDI(w), CTDI(vol)), and the dose-length product. Factors that affect radiation dose from CT include the beam energy, tube current-time product, pitch, collimation, patient size, and dose reduction options. Methods of reducing the radiation dose to a patient from CT include reducing the milliampere-seconds value, increasing the pitch, varying the milliampere-seconds value according to patient size, and reducing the beam energy. The effective dose from CT can be estimated by using Monte Carlo methods to simulate CT of a mathematical patient model, by estimating the energy imparted to the body region being scanned, or by using conversion factors for general anatomic regions. Issues related to radiation dose from CT are being addressed by the Society for Pediatric Radiology, the American Association of Physicists in Medicine, the American College of Radiology, and the Center for Devices and Radiological Health of the Food and Drug Administration.

Objective To investigate the feasibility of CT pulmonary angiography (CTPA) with 80 kVp and contrast agent of iodixanol (270 mg I/ml) by filtered back projection(FBP) reconstruction. Methods In total, 52 patients who underwent CTPA were randomly divided into two equally-sized groups, control group and experimental group. The volume computed tomography dose index (CTDIvol) and dose-length product(DLP)were recorded, and the weighted computed tomography dose index (CTDIw) and effective dose (E) were calculated. The image quality was visually evaluated and measured, and statistical analyses were performed on the image quality and the radiation dose. Results The sex, age, height, weight and body mass index (BMI) had no statistical difference between two groups (P>0.05). The average iodine dosage decreased by 22.9% in the experimental group compared with the control group. Compared with the control group, the CTDIvol, DLP, CTDIw and E decreased by 73.5%, 75.1%, 73.5% and 75.8%, respectively. The differences were statistically significant (t= 0.05). Conclusions Using 80 kVp and iodixanol for CTPA, FBP reconstruction image quality can meet diagnostic requirements. At the same time the radiation dose, the contrast agent dose and the X-ray tube wastage are reduced respectively. Key words: Radiation dose; Contrast medium; Pulmonary artery; CT pulmonary angiography; Filtered back projection

The purpose of this study was to compare the patient radiation dose and coronary artery image quality of long-z-axis whole-chest 64-MDCT performed with retrospective ECG gating with those of CT performed with prospective ECG triggering in the evaluation of emergency department patients with nonspecific chest pain. Consecutively registered emergency department patients with nonspecific low-to-moderate-risk chest pain underwent whole-chest CT with retrospective gating (n = 41) or prospective triggering (n = 31). Effective patient radiation doses were estimated and compared by use of unpaired Student's t tests. Two reviewers independently scored the quality of images of the coronary arteries, and the scores were compared by use of ordinal logistic regression. Age, heart rate, body mass index, and z-axis coverage were not statistically different between the two groups. For retrospective gating, the mean effective radiation dose was 31.8 +/- 5.1 mSv; for prospective triggering, the mean effective radiation dose was 9.2 +/- 2.2 mSv (prospective triggering 71% lower, p < 0.001). Two of 512 segments imaged with retrospective gating were nonevaluable (0.4%), and two of 394 segments imaged with prospective triggering were nonevaluable (0.5%). Prospectively triggered images were 2.2 (95% CI, 1.1-4.5) times as likely as retrospectively gated images to receive a high image quality score for each segment after adjustment for segment differences (p < 0.05). For long-z-axis whole-chest 64-MDCT of emergency department patients with nonspecific chest pain, use of prospective ECG triggering may result in substantially lower patient radiation doses and better coronary artery image quality than is achieved with retrospective ECG gating.

To measure the radiation dose profile, multiple-scan average dose (MSAD), and computed tomography dose index (CTDI) for electron beam CT and to determine the accuracy of ionization-chamber and manufacturer estimates of patient dose. High-resolution dose profiles along the longitudinal axis were acquired at several positions within the scan plane with use of radiographic film. The full-width-at-half-maximum values, peak radiation dose, CTDI, and MSAD were calculated from the digitized film profiles. CTDI was also measured with an ionization chamber. The full-width-half-maximum value of the radiation profiles were significantly wider than the nominal scan width for the 6-mm single-section and 8-mm multisection modes. In the single-section mode, the CTDI underestimated the MSAD by 15%-30%. The multisection radiation profile was nonuniform and asymmetric. Patient doses in electron beam CT are approximately 125% of the ionization-chamber CTDI measurements in the single-section mode. For the multisection mode, the average patient dose over the scan volume is approximately 70%-85% of the ionization-chamber CTDI measurements.

John Boone: Measurements and Indices in CT Dose Computed tomography has experienced rapid growth in utilization over the past 10 years, due in part to the dramatic increase in image quality and decrease in scan time that helical and multi‐slice CT scanners have allowed. This increased utilization has raised legitimate concerns about the radiation dose levels in CT. Traditional dose metrics such as the volume computed tomography index (CTDIvol) and the dose length product (DLP) will be discussed. The limitations of these metrics in the context of individual patient dosimetry will also be explained. In recent years, a number of new CT dose concepts have been introduced in the peer‐reviewed literature, in task group reports, and in other documents. A number of these new dose metrics will be discussed, including the rise‐to‐equilibrium‐dose, H(L), and the size‐specific dose estimate (SSDE). CT dosimetry has historically been performed used integrating ion chambers. In light of the dynamic scanning capabilities of modern CT scanners, the utility of a real‐time radiation meter will be discussed. Real‐time dose meters can substantially reduce the time required by the physicist in the CT scanner suite, while increasing the quantity and quality of the dose information that is measured. Niche applications include the rapid assessment of beam quality (half value layer) and the characterization of the beam shaping filters used in CT. In summary, this presentation will discuss existing CT dose parameters, and will then review a number of proposed new CT dose parameters which will likely be useful for CT dose assessment in the future. The recent growth of CT technology has outgrown the simple dose metrics of the past, and there is a need for the CT community to embrace new and more accurate CT dose metrics. Learning Objectives: 1. Identify and discuss the standard parameters used for reporting dose in computed tomography, including the volume CTDI, DLP, and effective dose using the k‐coefficients. 2. Identify and discuss parameters which influence the radiation dose to the patient, including patient size, dose modulation protocols, and scan length. 3. Discuss the limitations of using effective dose in describing radiation dose levels to individual patients. Dianna Cody: Estimating Patient Dose Although there are several methods in current use for estimating radiation dose delivered to individual patients, all have specific limitations that should be appreciated when they are utilized in the practice of clinical medical physics. Most patient dose estimates are based on fairly crude mathematical models of human anatomy and are unable to incorporate critical characteristics of patients such as their size and shape. Methods that are based on patient images (“voxelized patient models”) are available at few locations and are quite labor intensive. Recent improvements to patient dosimetry in CT, such as the size specific dose estimate (SSDE), may provide a path for reporting more customized patient dose estimates. Potential future options, and foreseeable pitfalls and complications, will be reviewed. Learning Objectives: 1. Recognize the limitations of current approaches to estimate CT patient dose. 2. Understand several methods available for estimating CT patient dose. 3. Understand potential future options for patient CT dose estimations. Tony Seibert Radiation over‐exposure for computed tomography (CT) perfusion studies occurring in the 2008–2009 timeframe resulted in California Senate Bill 1237, legislation that was authored by Senator Padilla in response to these incidents. The legislation was signed by the Governor in September 2010. The law contains three parts: (1) Recording CT dose indices for each patient, placing these values in the radiology report, and verifying accuracy of the volume Computed Tomography Dose Index (CTDIvol); (2) Requiring accreditation for all CT scanners performing diagnostic exams that are under the authority of the California Department of Public Health; (3) Reporting of radiation exposures that exceed specified limits to organs, cause unanticipated erythema or hair loss, or inappropriate irradiation to body parts not ordered by a physician. Part 1 of the law commenced on July 1, 2012, and the other two parts are to commence on July 1, 2013. This presentation describes the steps taken to comply specifically with Part 1 and 3 of the law. To ensure compliance, an automated extraction and delivery of the CTDIvol and DLP indices to the radiology report were implemented. However, the legislation does not provide guidance on how to: (1) adjust CTDIvol for patient size; (2) deal with CT exams having multiple different series, each with individual dose indices; (3) sum CTDIvol and DLP for the same or different body areas scanned (if appropriate). The consequence is variable reporting at the initial implementation of the law, which requires standardized reporting metrics. Recommendations by the University of California Dose Optimization and Standardization Endeavor (UC DOSE) is discussed in this context, with relevant solutions described and specific examples demonstrated. To conclude, an update from the users perspective of compliance, as well as reporting of the status from the State of California Department of Public Health office is provided. Learning Objectives: 1. Describe the provisions of the California State law on dose reporting for computed tomography (CT) scanners. 2. Demonstrate ways in which the required elements volume Computed Tomography Dose Index (CTDIvol) and Dose Length Product (DLP) can be placed into the radiology report. 3. Discuss discrepancies regarding the relationship between CTDIvol and patient dose, and issues in accumulating dose indices for CT scans in a multi‐series exam and for individual exams over time. 4. Report on the status of compliance with the statutes of the law.

Computed tomography (CT) is a widely utilized diagnostic imaging modality in medicine. However, the potential risks associated with radiation exposure necessitate investigating CT exams to minimize unnecessary radiation. The objective of this study is to evaluate how patient-related parameters impact the CT dose indices for different CT exams. In this study, a dataset containing CT dose information for a cohort of 333 patients categorized into four CT exams, chest, cardiac angiogram, cardiac calcium score and abdomen/pelvis, was collected and retrospectively analyzed. Regression analysis and Pearson correlation were applied to estimate the relationships between patient-related factors, namely body mass index (BMI), weight and age as input variables, and CT dose indices, namely the volume CT dose index (CTDIvol), dose length product (DLP), patient effective dose (ED) and size-specific dose estimate (SSDE), as output variables. Moreover, the study investigated the correlation between the different CT dose indices. Using linear regression models and Pearson correlation, the study found that all CT dose indices correlate with BMI and weight in all CT exams with varying degrees as opposed to age, which did not demonstrate any significant correlation with any of the CT dose indices across all CT exams. Moreover, it was found that using multiple regression models where multiple input variables are considered resulted in a higher correlation with the output variables than when simple regression was used. Investigating the relationships between the different dose indices, statistically significant relationships were found between all dose indices. A stronger linear relationship was noticed between CTDIvol and DLP compared to the relationships between each pair of the other dose indices. The findings of this study contribute to understanding the relationships between patient-related parameters and CT dose indices, aiding in the development of optimized CT exams that ensure patient safety while maintaining the diagnostic efficacy of CT imaging.

Background:Presently, computed tomography (CT) is the most important source of medical radiation exposure. CT radiation doses vary considerably across institutions depending on the protocol and make of equipment. India does not yet have national or region-specific CT diagnostic reference levels.Aim:To evaluate radiation doses of consecutive multidetector CT (MDCT) examinations based on anatomic region, performed in 1 month, collected simultaneously from seven tertiary care hospitals in Kerala.Settings and Design:Descriptive study.Materials and Methods:We collected the CT radiation dose data of examinations from the seven collaborating tertiary care hospitals in Kerala, performed with MDCT scanners of five different makes. The data included anatomic region, number of phases, CT dose index (CTDIvol), dose-length product (DLP), and effective dose (ED) of each examinations and patient demographic data.Statistical Analysis:We calculated the 25th, 50th, and 75th percentiles of the CTDIvol, DLP, and ED according to anatomic region. We made descriptive comparisons of these results with corresponding data from other countries.Results:Of 3553 patients, head was the most frequently performed examination (60%), followed by abdomen (19%). For single-phase head examinations, 75th percentile of CTDIvol was 68.1 mGy, DLP 1120 mGy-cm, and ED 2.1 mSv. The 75th percentiles of CTDIvol, DLP, and ED for single-phase abdomen examinations were 10.6, 509.3, and 7.7, and multiphase examinations were 14.6, 2666.9, and 40.8; single-phase chest examinations were 23.4, 916.7, and 13.38, and multiphase examinations were 19.9, 1737.6, and 25.36; single-phase neck were 24.9, 733.6, and 3.814, and multiphase neck were 24.9, 2076, and 10.79, respectively.Conclusion:This summary CT radiation dose data of most frequently performed anatomical regions could provide a starting point for institutional analysis of CT radiation doses, which in turn leads to meaningful optimization of CT.

The IAEA — UAE Project on Patient Radiation Protection aimed at evaluating radiation dose levels received by patients during radiological examinations. In this paper, we are presenting the preliminary results of patient doses in Computed Tomography (CT) examinations at 4 UAE hospitals (3 major governmental hospitals and 1 private). Five Multi-slice CT (MSCT) systems (4S, 16S and 64S) were included in this study. All these systems are enrolled in quality control program. CT dose levels were evaluated through either thermoluminescent detectors (TLD-100) or by using Head (16-cm Diameter) and Body (32-cm Diameter) cylindrical CTDI PMMA phantom fitted with a 10 cm pencil ionization chamber. Adult and pediatric patient CT doses were collected from common CT examinations of the Head, Chest and Abdomen & Pelvis. The CT Dose Index (CTDIvol), Dose Length Product (DLP) and Effective Doses (E) were the main CT dosimetry parameters evaluated in this project. The CTDIvol results of all CT systems showed acceptable compliance with those reported by professional organizations. The range of 3rd quartile of adult DLP values for CT Head examinations among the 4 hospitals was 384.106–5031.92 mGy.cm. The adult CT Chest examinations demonstrated the range of the 3rd quartile DLP values between 122.035–1423.06 mGy.cm while the Abdomen & Pelvis examinations showed a range of 258.446–1701.135 mGy.cm. Hospitals DD3, AA13 and ANM14 are within the UAE initial adapted local Dose Reference Levels (DRLs) and are comparable to the European guidelines while hospitals TA1 and TA2 are higher. The CT effective doses of almost all the examination types were within the level mentioned by international organizations such as the ICRP (Report 102, 2007) with the exception of CT examinations performed at TA1 & TA2. Further work is developed to reduce patient radiation doses of the common CT examinations of the Head, Chest and Abdomen & Pelvis. Adult and pediatric patient data collection and analysis of CT doses from other hospitals at the UAE are in progress.

Objective To evaluate the effect of reference mAs on radiation dose and image quality characteristics of chest CT scanned with CARE kV technique compared with CARE Dose4D. Methods According to the date of examination,158 consecutive patients were selected in our department and randomly divided into 5 groups: CARE Dose4D group (30 cases, group 1); using CARE kV technology, reference mAs were 110 (32 cases), 90 (31 cases), 70 (33 cases), 50 (32 cases), which were recorded asthe group from 2 to 5, respectively. Volume CT dose index (CTDIvol), dose length product (DLP) and the effective dose (ED) were analyzed. CT value and objective image noise were measured in the lungparenchyma and descending aorta.Two radiologists assessed the images for subjective noise, artefacts and diagnostic acceptability.The radiation dose, CT value and objective noise were compared with the analysis of variance, and the difference between two groups was compared with SNK test; the rank sum tests (Kruskal-Wallis) were used in subjective image quality score, and difference between two groups was compared with K-W test. Results The CTDIvol, DLP, ED values in five groups were(7.7±1.7),(7.7±2.0), (5.5±1.4), (4.2±1.5), (2.8±1.2)mGy, (290.7±67.4) , (290.1±85.2) , (194.2±52.1) , (150.7±63.8) , (96.5±38.9) mGy·cm, (4.1±0.9) , (4.1±1.2) , (2.7±0.7) , (2.1±0.9) , (1.3±0.5) mSv, respectively.There were significant difference among the 5 groups(F=59.305, 57.76, 57.76, P 0.05). The objective noise of 5 groups in pulmonary parenchyma and the descending aorta were (48.7±9.1) , (49.2±10.0) , (55.5±11.2) , (56.5±8.3) , (63.7±13.2) HU; (9.2±1.6) , (9.5 ± 2.1) , (10.7 ± 2.6) , (11.6 ± 2.7) , (13.6 ± 2.6) HU respectively, and the difference was significant(F= 10.774, 17.157, P 0.05). Conclusion Comparedwith CARE Dose4D, the use of CARE kV technique of suitable reference mAs for unenhanced chest CT can reduce radiation dose significantly with diagnostically acceptable image quality. Key words: Tomography, X-ray computed; Radiation dosage

CT guidance is increasingly being used to localize the epidural space during epidural steroid injections. A common concern is that CT may be associated with significantly higher radiation doses compared with conventional fluoroscopy. The goal of this retrospective study was to determine the average dose-length product and effective dose delivered while interlaminar epidural steroid injections are performed and allow comparison with other modalities. A total of 281 patients who had undergone 345 consecutive CT-guided epidural steroid injections of the lumbar spine were evaluated for radiation exposure. The dose-length product for each scan was derived from the CT dose index volume and scan length. Effective dose was then calculated from the dose-length product and a κ coefficient of 0.015. Procedure time was calculated from the PACS time stamp on the scout image to the last CT image of the last image series. The average dose-length product across all procedures was 89.6 ± 3.33 mGy·cm, which represents an effective dose of 1.34 ± 0.05 mSv. No complications from the procedure were observed, and average procedure time was 8 minutes. The use of a stationary table and an intermittent scanning technique allow for short procedures and doses that are significantly lower than those of conventional diagnostic CT scans. Furthermore, because CT dose index overestimates radiation dose in stationary table procedures, the actual radiation dose may be even lower than stated here.