Optimizing Radiation Doses for Computed Tomography Across Institutions: Dose Auditing and Best Practices

Computed Tomography of the Head : A Systematic Review on Acquisition and Reconstruction Techniques to Reduce Radiation Dose

In 1971, the first computed tomography (CT) scan was performed on a patient's brain. Clinical CT systems were introduced in 1974 and dedicated to head imaging only. New technological developments, broader availability, and the clinical success of CT led to a steady growth in examination numbers. Most frequent indications for non-contrast CT (NCCT) of the head include the assessment of ischemia and stroke, intracranial hemorrhage and trauma, while CT angiography (CTA) has become the standard for first-line cerebrovascular evaluation; however, resulting improvements in patient management and clinical outcomes come at the cost of radiation exposure, increasing the risk for secondary morbidity. Therefore, radiation dose optimization should always be part of technical advancements in CT imaging but how can the dose be optimized? What dose reduction can be achieved without compromising diagnostic value, and what is the potential of the upcoming technologies artificial intelligence and photon counting CT? In this article, we look for answers to these questions by reviewing dose reduction techniques with respect to the major clinical indications of NCCT and CTA of the head, including a brief perspective on what to expect from current and future developments in CT technology with respect to radiation dose optimization.

National Imaging Trends for Suspected Urinary Stone Disease in the Emergency Department

This cohort study examines the use of an ultrasonography-first strategy for urinary stone disease.

Computed Tomography of the Spine

The introduction of the first whole-body CT scanner in 1974 marked the beginning of cross-sectional spine imaging. In the last decades, the technological advancement, increasing availability and clinical success of CT led to a rapidly growing number of CT examinations, also of the spine. After initially being primarily used for trauma evaluation, new indications continued to emerge, such as assessment of vertebral fractures or degenerative spine disease, preoperative and postoperative evaluation, or CT-guided interventions at the spine; however, improvements in patient management and clinical outcomes come along with higher radiation exposure, which increases the risk for secondary malignancies. Therefore, technical developments in CT acquisition and reconstruction must always include efforts to reduce the radiation dose. But how exactly can the dose be reduced? What amount of dose reduction can be achieved without compromising the clinical value of spinal CT examinations and what can be expected from the rising stars in CT technology: artificial intelligence and photon counting CT? In this article, we try to answer these questions by systematically reviewing dose reduction techniques with respect to the major clinical indications of spinal CT. Furthermore, we take a concise look on the dose reduction potential of future developments in CT hardware and software.

Anteroposterior pelvic radiograph is not sufficient to confirm hip reduction after conservative treatment of developmental dysplasia of the hip

The purpose of this study was to investigate whether an anteroposterior pelvic radiograph alone is sufficient to confirm hip reduction after conservative treatment or whether MRI could be alternatively performed. A total of 133 children (145 hips) were enrolled. All children were examined by anteroposterior pelvic radiographs and MRI. Three experts interpreted anteroposterior pelvic radiographs and then verified these results on MRI. For patients with inconsistent results between anteroposterior pelvic radiographs and MRI, the continuity of Shenton's line and Calve's line was recorded, and the medial clear space of bilateral hips was measured for unilateral cases. There was complete agreement between the three experts in the interpretation of anteroposterior pelvic radiographs of 111 (76.55%) hips; there was disagreement in the remaining 34 hips, with two experts diagnosing satisfactory reduction in 13 hips and dislocation in 21 hips. Assuming that the judgment of two or more doctors on anteroposterior pelvic radiographs was taken as the final result, 17 hips (11.72%) were misjudged. There was no statistically significant difference between the actual in-position group and the actual dislocation group in terms of the continuity of Shenton's line ( P  = 0.62) and Calve's line ( P  = 0.10) and the medial clear space of bilateral hips ( P  = 0.08). In children less than 1 year of age with developmental dysplasia of the hip treated conservatively, the use of anteroposterior pelvic radiographs alone to judge hip reduction might result in misdiagnosis and missed diagnosis. MRI could be alternatively used to detect hip reduction after conservative treatment, especially when the doctor was not familiar with ultrasound in the presence of plaster.

Clinical assessment of head injuries in motorcyclists involved in traffic accidents: A prospective, observational study

OBJECTIVE

to review the clinical assessment of head injuries in motorcyclists involved in traffic accidents.

METHOD

prospective observational study, including adult motorcyclists involved in traffic accidents in a period of 12 months. Patients sustaining signs of intoxication were excluded. A modification of the Canadian Head CT Rules was used to indicate computed tomography (CT). Patients not undergoing CT were followed by phone calls for three months. Collected variables were compared between the group sustaining head injuries and the others. We used chi-square, Fisher, and Student's t for statistical analysis, considering p<0.05 as significant.

RESULTS

we included 208 patients, 99.0% were wearing helmets. Seventeen sustained signs of intoxication and were excluded. Ninety (47.1%) underwent CT and 12 (6.3%) sustained head injuries. Head injuries were significantly associated with Glasgow Coma Scale<15 (52.3% vs. 2.8% - p<0,001) and a positive physical exam (17.1% vs. zero - p<0,05). Four (2.1%) patients with intracranial mass lesions needed surgical interventions. None helmet-wearing patients admitted with GCS=15 and normal physical examination sustained head injuries.

CONCLUSION

Head CT is not necessary for helmet-wearing motorcyclists admitted with GCS=15 and normal physical examination.

Strategies for Dose Optimization: Views From Health Care Systems

BACKGROUND

Advances in CT have facilitated widespread use of medical imaging while increasing patient lifetime exposure to ionizing radiation.

PURPOSE

To describe dose optimization strategies used by health care organizations to optimize radiation dose and image quality.

MATERIALS AND METHODS

A qualitative study of semistructured interviews conducted with 26 leaders from 19 health care systems in the United States, Europe, and Japan. Interviews focused on strategies that were used to optimize radiation dose at the organizational level. A directed content analysis approach was used in data analysis.

RESULTS

Analysis identified seven organizational strategies used by these leaders for optimizing CT dose: (1) engaging radiologists and technologists, (2) establishing a CT dose committee, (3) managing organizational change, (4) providing leadership and support, (5) monitoring and benchmarking, (6) modifying CT protocols, and (7) changes in equipment and work rules.

CONCLUSIONS

Leaders in these health systems engaged in specific strategies to optimize CT dose within their organizations. The strategies address challenges health systems encounter in optimizing CT dose at the organizational level and offer an evolving framework for consideration in dose optimization efforts for enhancing safety and use of medical imaging.

Investigação da presença de lesões traumáticas em segmento cefálico em motociclistas vítimas de acidentes de tráfego: Estudo observacional prospectivo

RESUMO Objetivo: análise crítica da investigação diagnóstica de lesões em segmento cefálico de motociclistas vítimas de acidentes de tráfego. Método: estudo observacional prospectivo incluindo motociclistas adultos vítimas de trauma, sem intoxicação exógena, em um período de 12 meses. A tomografia de crânio (TC) foi indicada de acordo com uma modificação dos “critérios canadenses”. Os pacientes que não foram submetidos a TC de crânio tiveram acompanhamento telefônico por três meses. A presença de lesões foi correlacionada com as varáveis coletadas através dos testes Qui-quadrado, t de Student ou Fisher, considerando p<0,05 como significativo. Resultados: dos 208 inicialmente incluídos, 206 (99,0%) estavam usando capacete. Dezessete estavam com sinais de intoxicação exógena e foram excluídos, restando 191 para análise. Noventa pacientes (47,1%) realizaram TC e 12 (6,3%) apresentaram lesões craniencefálicas, que se associaram significativamente a Escala de Coma de Glasgow (ECG) <15 (52,3% vs. 2,8% - p<0,001) e alterações ao exame físico da região cefálica/neurológico (17,1% vs. zero - p<0,05). Quatro pacientes (2,1%) precisaram tratamento cirúrgico de lesões intracranianas. Nenhum dos pacientes admitidos com ECG 15, em uso de capacete e sem alterações no exame físico apresentou TC alterada. Conclusões: para pacientes admitidos com ECG 15, que utilizavam o capacete no acidente e não apresentavam quaisquer alterações no exame físico, a realização da TC de crânio não trouxe mudanças no atendimento ao paciente. .

Simplified size adjusted dose reference levels for adult CT examinations: A regional study

PURPOSE

To investigate retrospective classification of adult patients into small, average, and large based on effective diameter (EDia) from localizer image of computed tomography (CT) scans and to develop regional diagnostic reference levels (DRLs) and achievable doses (AD).

METHOD

The patients falling within the mean ± standard deviation (SD) of EDia were classified as average; those below this range as small and above as large. The CTDI_vol,dose-length-product (DLP) and size-specific dose estimates (SSDE) of all adult patients undergoing CT examinations in 8 CT facilities for 11 months (Dec. 2019 - Oct. 2020) were evaluated. The 75th and 50th percentile values were compared with national and international values.

RESULTS

Of the total of 69,434 CT examinations, nearly 80% fell within average size. The 75th percentile values of CTDI_vol and DLP for small patients for abdomen-pelvic exams were nearly half of average sized patients. Similarly, the 75th percentile values for large patients were nearly double. Similar findings were not found for chest exams. Analysis of image quality and dose factors such as noise, mean axial length, slice thickness, mean number of sequences, use of iterative reconstruction and tube current modulation (TCM) resulted in identification of opportunities for improvement and optimization of different CT facilities.

CONCLUSIONS

DRLs for adult patients were found to vary widely with patient size and thus establishing DRLs only for standard sized patient is not adequate. Simplified and intuitive methods for size classification was shown to provide meaningful information for optimization for patients outside the standard size adult.

Task-based assessment of neck CT protocols using patient-mimicking phantoms-effects of protocol parameters on dose and diagnostic performance

Objectives

To assess how modifying multiple protocol parameters affects the dose and diagnostic performance of a neck CT protocol using patient-mimicking phantoms and task-based methods.

Methods

Six patient-mimicking neck phantoms containing hypodense lesions of 1 cm diameter and 30 HU contrast and one non-lesion phantom were examined with 36 CT protocols. All possible combinations of the following parameters were investigated: 100- and 120-kVp tube voltage; tube current modulation (TCM) noise levels of SD 7.5, 10, and 14; pitches of 0.637, 0.813, and 1.388; filtered back projection (FBP); and iterative reconstruction (AIDR 3D). Dose-length products (DLPs) and lesion detectability (assessed by 14 radiologists) were compared with the clinical standard protocol (120 kVp, TCM SD 7.5, 0.813 pitch, AIDR 3D).

Results

The DLP of the standard protocol was 25 mGy•cm; the area under the curve (AUC) was 0.839 (95%CI: 0.790–0.888). Combined effects of tube voltage reduction to 100 kVp and TCM noise level increase to SD 10 optimized protocol performance by improving dose (7.3 mGy•cm) and detectability (AUC 0.884, 95%CI: 0.844–0.924). Diagnostic performance was significantly affected by the TCM noise level at 120 kVp (AUC 0.821 at TCM SD 7.5 vs. 0.776 at TCM SD 14, p = 0.003), but not at 100-kVp tube voltage (AUC 0.839 at TCM SD 7.5 vs. 0.819 at TCM SD 14, p = 0.354), the reconstruction method at 100 kVp (AUC 0.854 for AIDR 3D vs. 0.806 for FBP, p < 0.001), but not at 120-kVp tube voltage (AUC 0.795 for AIDR 3D vs. 0.793 for FBP, p = 0.822), and the tube voltage for AIDR 3D reconstruction (p < 0.001), but not for FBP (p = 0.226).

Conclusions

Combined effects of 100-kVp tube voltage, TCM noise level of SD 10, a pitch of 0.813, and AIDR 3D resulted in an optimal neck protocol in terms of dose and diagnostic performance. Protocol parameters were subject to complex interactions, which created opportunities for protocol improvement.

Key Points

• A task-based approach using patient-mimicking phantoms was employed to optimize a CT system for neck imaging through systematic testing of protocol parameters.

• Combined effects of 100-kVp tube voltage, TCM noise level of SD 10, a pitch of 0.813, and AIDR 3D reconstruction resulted in an optimal protocol in terms of dose and diagnostic performance.

• Interactions of protocol parameters affect diagnostic performance and should be considered when optimizing CT techniques.

Electronic supplementary material

The online version of this article (10.1007/s00330-020-07374-8) contains supplementary material, which is available to authorized users.

Adult patient-specific CT organ dose estimations using automated segmentations and Monte Carlo simulations

We aimed to determine feasibility in calculating patient-specific organ doses for abdominal computed tomography (CT) exams using an automated segmentation technique dedicated to abdominal organs combined with Monte Carlo simulation of a clinical CT scanner. We conducted the automated segmentation of five major abdominal organs (left and right kidneys, pancreas, spleen, and liver) for ten adult patients and calculated organ-specific doses for each patient. We observed significant variability (Coefficient of Variation up to 32%) in organ mass across the ten patients, which was up to two-fold greater or smaller than the reference organ mass for the ICRP reference adult male and female. Comparison of patient-specific organ dose per CTDI_vol with those from the ICRP reference phantoms confirmed that reference phantom-based dose reporting programs cannot capture inter-patient dose variability, and dosimetric errors can go up to nearly 40%. We demonstrated an automated method for patient-specific organ dose calculations, which took about 45 min per patient. When the automatic segmentation method is extended to more organs and faster Monte Carlo calculation technique is employed, our method should be useful for patient-specific dose monitoring at the organ level and for epidemiological investigations of health risks in CT patients.

Comparison of the Effectiveness of Single-Component and Multicomponent Interventions for Reducing Radiation Doses in Patients Undergoing Computed Tomography: A Randomized Clinical Trial

Importance

Computed tomography (CT) radiation doses vary across institutions and are often higher than needed.

Objective

To assess the effectiveness of 2 interventions to reduce radiation doses in patients undergoing CT.

Design, Setting, and Participants

This randomized clinical trial included 864 080 adults older than 18 years who underwent CT of the abdomen, chest, combined abdomen and chest, or head at 100 facilities in 6 countries from November 1, 2015, to September 21, 2017. Data analysis was performed from October 4, 2017, to December 14, 2018.

Interventions

Imaging facilities received audit feedback alone comparing radiation-dose metrics with those of other facilities followed by the multicomponent intervention, including audit feedback with targeted suggestions, a 7-week quality improvement collaborative, and best-practice sharing. Facilities were randomly allocated to the time crossing from usual care to the intervention.

Main Outcomes and Measures

Primary outcomes were the proportion of high-dose CT scans and mean effective dose at the facility level. Secondary outcomes were organ doses. Outcomes after interventions were compared with those before interventions using hierarchical generalized linear models adjusting for temporal trends and patient characteristics.

Results

Across 100 facilities, 864 080 adults underwent 1 156 657 CT scans. The multicomponent intervention significantly reduced proportions of high-dose CT scans, measured using effective dose. Absolute changes in proportions of high-dose scans were 1.1% to 7.9%, with percentage reductions in the proportion of high-dose scans of 4% to 30% (abdomen: odds ratio [OR], 0.82; 95% CI, 0.77-0.88; P < .001; chest: OR, 0.92; 95% CI, 0.86-0.99; P = .03; combined abdomen and chest: OR, 0.49; 95% CI, 0.41-0.59; P < .001; and head: OR, 0.71; 95% CI, 0.66-0.76; P < .001). Reductions in the proportions of high-dose scans were greater when measured using organ doses. The absolute reduction in the proportion of high-dose scans was 6.0% to 17.2%, reflecting 23% to 58% reductions in the proportions of high-dose scans across anatomical areas. Mean effective doses were significantly reduced after multicomponent intervention for abdomen (6% reduction, P < .001), chest (4%, P < .001), and chest and abdomen (14%, P < .001) CT scans. Larger reductions in mean organ doses were 8% to 43% across anatomical areas. Audit feedback alone reduced the proportions of high-dose scans and mean dose, but reductions in observed dose were smaller. Radiologist's satisfaction with CT image quality was unchanged and high during all periods.

Conclusions and Relevance

For imaging facilities, detailed feedback on CT radiation dose combined with actionable suggestions and quality improvement education significantly reduced doses, particularly organ doses. Effects of audit feedback alone were modest.

Trial Registration

ClinicalTrials.gov Identifier: NCT03000751.

Analysis of Computed Tomography Radiation Doses Used for Lung Cancer Screening Scans

IMPORTANCE

The American College of Radiology (ACR) has recognized the importance of minimizing radiation doses used for lung cancer screening (LCS) computed tomography (CT). However, without standard protocols, doses could still be unnecessarily high, reducing screening margin of benefit.

OBJECTIVE

To characterize LCS CT radiation doses and identify factors explaining variation.

DESIGN, SETTING, AND PARTICIPANTS

We prospectively collected LCS examination dose metrics, from 2016 to 2017, at US institutions in the University of California, San Francisco International Dose Registry. Institution-level factors were collected through baseline survey. Mixed-effects linear and logistic regression models were estimated using forward variable selection. Results are presented as percentage excess dose and odds ratios (ORs) with 95% confidence intervals (CIs). The analysis was conducted between 2018 and 2019.

MAIN OUTCOMES AND MEASURES

Log-transformed measures of (1) mean volume CT dose index (CTDIvol, mGy), reflecting the average radiation dose per slice; (2) mean effective dose (ED, mSv), reflecting the total dose received and estimated future cancer risk; (3) proportion of CT scans using radiation doses above ACR benchmarks (CTDIvol >3 mGy, ED >1 mSv); and (4) proportion of CT scans using radiation doses above 75th percentile of registry doses (CTDIvol >2.7 mGy, ED >1.4 mSv).

RESULTS

Data were collected for 12 529 patients undergoing LCS CT scans performed at 72 institutions. Overall, 7232 participants (58%) were men, and the median age was 65 years (interquartile range [IQR], 60-70). Of 72 institutions, 15 (21%) had median CTDIvol and 47 (65%) had median ED above ACR guidelines. Institutions allowing any radiologists to establish protocols had 44% higher mean CTDIvol (mean dose difference [MDD], 44%; 95% CI, 19%-69%) and 27% higher mean ED (MDD, 27%; 95% CI, 5%-50%) vs those limiting who established protocols. Institutions allowing any radiologist to establish protocols had higher odds of examinations exceeding ACR CTDIvol guidelines (OR, 12.0; 95% CI, 2.0-71.4), and 75th percentile of registry CTDIvol (OR, 19.0; 95% CI, 1.9-186.7) or ED (OR, 8.5; 95% CI, 1.7-42.9). Having lead radiologists establish protocols resulted in lower odds of doses exceeding ACR ED guidelines (OR, 0.01; 95% CI, 0.001-0.1). Employing external vs internal medical physicists was associated with increased odds of exceeding ACR CTDIvol guidelines (OR, 6.1; 95% CI, 1.8-20.8). Having medical physicists establish protocols was associated with decreased odds of exceeding 75th percentile of registry CTDIvol (OR, 0.09; 95% CI, 0.01-0.59). Institutions reporting protocol updates as needed had 27% higher mean CTDIvol (MDD, 27%; 95% CI, 8%-45%).

CONCLUSIONS AND RELEVANCE

Facilities varied in LCS CT radiation dose distributions. Institutions limiting protocol creation to lead radiologists and having internal medical physicists had lower doses.

Predictors of radiation dose for CT pulmonary angiography in pregnancy across a multihospital integrated healthcare network

PURPOSE

There is a large range of published effective radiation dose for CTPA during pregnancy. The purpose of our study is to determine the mean effective radiation dose and predictors of mean effective radiation dose for CTPA in pregnant patients across a multihospital integrated healthcare network.

METHODS

This retrospective study evaluates pregnant women who had a CTPA as the first primary advanced imaging test for evaluation of PE in a multihospital integrated healthcare network from January 2012-April 2017. Patient and CT-related data were obtained from the electronic health record and Radimetrics server (Radimetrics Inc, Bayer). DLP was recorded and effective radiation dose in mSv was determined using a conversation factor of 0.014 mSv·mGy^-¹·cm^-¹. Patient size was determined by water equivalent diameter. Bivariate and multivariate analysis were performed for effective radiation dose based on patient and CT factors.

RESULTS

In the 534 CTPA exams, the mean effective radiation dose was 3.96 mSv. Bivariate analysis showed significant differences in radiation dose by trimester, p = 0.042: first trimester 4.52 mSv, second trimester 3.73 mSv, and third trimester 3.95 mSv. Multivariable analysis demonstrated CTPA during first trimester, increasing mAs, kVp, scan length, patient size, and use of mAs modulation, as well as decreasing pitch, to be predictive of higher effective radiation dose.

CONCLUSION

Mean effective radiation dose was on the lower end of published studies. Trimester was a statistically significant predictor of effective radiation dose when accounting for known predictors of radiation dose.

Comparison of the Harms, Advantages, and Costs Associated With Alternative Guidelines for the Evaluation of Hematuria

IMPORTANCE

Existing recommendations for the diagnostic testing of hematuria range from uniform evaluation of varying intensity to patient-level risk stratification. Concerns have been raised about not only the costs and advantages of computed tomography (CT) scans but also the potential harms of CT radiation exposure.

OBJECTIVE

To compare the advantages, harms, and costs associated with 5 guidelines for hematuria evaluation.

DESIGN, SETTING, AND PARTICIPANTS

A microsimulation model was developed to assess each of the following guidelines (listed in order of increasing intensity) for initial evaluation of hematuria: Dutch, Canadian Urological Association (CUA), Kaiser Permanente (KP), Hematuria Risk Index (HRI), and American Urological Association (AUA). Participants comprised a hypothetical cohort of patients (n = 100 000) with hematuria aged 35 years or older. This study was conducted from August 2017 through November 2018.

EXPOSURES

Under the Dutch and CUA guidelines, patients received cystoscopy and ultrasonography if they were 50 years or older (Dutch) or 40 years or older (CUA). Under the KP and HRI guidelines, patients received different combinations of cystoscopy, ultrasonography, and CT urography or no evaluation on the basis of risk factors. Under the AUA guidelines, all patients 35 years or older received cystoscopy and CT urography.

MAIN OUTCOMES AND MEASURES

Urinary tract cancer detection rates, radiation-induced secondary cancers (from CT radiation exposure), procedural complications, false-positive rates per 100 000 patients, and incremental cost per additional urinary tract cancer detected.

RESULTS

The simulated cohort included 100 000 patients with hematuria, aged 35 years or older. A total of 3514 patients had urinary tract cancers (estimated prevalence, 3.5%; 95% CI, 3.0%-4.0%). The AUA guidelines missed detection for the fewest number of cancers (82 [2.3%]) compared with the detection rate of the HRI (116 [3.3%]) and KP (130 [3.7%]) guidelines. However, the simulation model projected 108 (95% CI, 34-201) radiation-induced cancers under the KP guidelines, 136 (95% CI, 62-229) under the HRI guidelines, and 575 (95% CI, 184-1069) under the AUA guidelines per 100 000 patients. The CUA and Dutch guidelines missed detection for a larger number of cancers (172 [4.9%] and 251 [7.1%]) but had 0 radiation-induced secondary cancers. The AUA guidelines cost approximately double the other 4 guidelines ($939/person vs $443/person for Dutch guidelines), with an incremental cost of $1 034 374 per urinary tract cancer detected compared with that of the HRI guidelines.

CONCLUSIONS AND RELEVANCE

In this simulation study, uniform CT imaging for patients with hematuria was associated with increased costs and harms of secondary cancers, procedural complications, and false positives, with only a marginal increase in cancer detection. Risk stratification may optimize the balance of advantages, harms, and costs of CT.

Cumulative Doses of Ionizing Radiation From Computed Tomography: A Population-Based Study

OBJECTIVE

To assess cumulative radiation doses from computed tomography (CT), patient characteristics, and clinical indications for CT in a population-based sample.

PATIENTS AND METHODS

A cohort study using medical records linkage through the Rochester Epidemiology Project was conducted to ascertain all CT examinations in Olmsted County, Minnesota, performed between January 1, 2004, and December 31, 2013, among all adults who were alive for 3 or more years after the end of follow-up (to exclude exposures preceding death). Ten-year cumulative effective ionizing radiation doses were estimated on the basis of typical doses per CT modality. Among patients with high doses (≥100 mSv/10 years), CT scans were reviewed for clinical setting, indications, and results.

RESULTS

Of 54,447 adults (median age, 44.0 years at inclusion), 26,377 (48.4%) underwent at least one CT. Ten-year radiation doses from CT were 0.1 to 9.9 mSv in 15.8% of the population (8593 patients), 10 to 24.9 mSv in 16.9% (9502), 25 to 99.9 mSv in 13.8% (7492), and 100 mSv or greater in 1.9% (1041). Computed tomography of the abdomen and pelvis accounted for 67.2% of the estimated dose. In multivariable models, doses differed 1.21-fold to 2.16-fold between extreme categories of age, body mass index, education level, smoking status, and by race. Of 600 CTs in 200 patients with high doses, 70.5% were obtained for restaging of solid cancers and lymphoma, abdominal pain, infection, kidney stones, follow-up of nodules or masses, and chest pain/evaluation for pulmonary embolism.

CONCLUSION

Exposure to ionizing radiation from CT occurred disproportionally in specific subgroups of the population. A limited number of clinical indications contributed the majority of radiation among adults with high doses.

Outcompeting p53-Mutant Cells in the Normal Esophagus by Redox Manipulation

As humans age, normal tissues, such as the esophageal epithelium, become a patchwork of mutant clones. Some mutations are under positive selection, conferring a competitive advantage over wild-type cells. We speculated that altering the selective pressure on mutant cell populations may cause them to expand or contract. We tested this hypothesis by examining the effect of oxidative stress from low-dose ionizing radiation (LDIR) on wild-type and p53 mutant cells in the transgenic mouse esophagus. We found that LDIR drives wild-type cells to stop proliferating and differentiate. p53 mutant cells are insensitive to LDIR and outcompete wild-type cells following exposure. Remarkably, combining antioxidant treatment and LDIR reverses this effect, promoting wild-type cell proliferation and p53 mutant differentiation, reducing the p53 mutant population. Thus, p53-mutant cells can be depleted from the normal esophagus by redox manipulation, showing that external interventions may be used to alter the mutational landscape of an aging tissue.

Characterization of office laser printers for 3-D printing of soft tissue CT phantoms

The purpose of our study is to develop and evaluate a method for radiopaque 3-D printing (R3P) of soft tissue computed tomography (CT) phantoms with office laser printers. Five laser printers from different vendors are tested for toner CT attenuation. A liver phantom is created by printing CT images of a patient liver on office paper. One thousand eight hundred sixty paper sheets are printed with three repeated prints per page, resulting in a stack of 18.6 cm. The phantom is examined with 12 tube current settings. Images are reconstructed using filtered back projection (FBP) and iterative reconstruction [adaptive iterative dose reduction 3D (AIDR 3D)]. Seven radiologists rated image quality of all acquisitions. Toner attenuation of all investigated printers increased linearly with the print template grayscale. The liver phantom reproduced anatomic detail and attenuation values of the patient ( mean ± SD HU difference 12.68 ± 7.74 ). Image quality scores increased with dose but did not vary significantly above a threshold dose for AIDR 3D. Overall, AIDR 3D reconstructed images are rated superior to FBP reconstructions ( p < 0.001 ). In conclusion, R3P with standard office laser printers can generate soft tissue CT phantoms without hardware manipulations but with limited flexibility regarding attenuation properties of the printed toner material.

International variation in radiation dose for computed tomography examinations: prospective cohort study

OBJECTIVE

To determine patient, institution, and machine characteristics that contribute to variation in radiation doses used for computed tomography (CT).

DESIGN

Prospective cohort study.

SETTING

Data were assembled and analyzed from the University of California San Francisco CT International Dose Registry.

PARTICIPANTS

Standardized data from over 2.0 million CT examinations of adults who underwent CT between November 2015 and August 2017 from 151 institutions, across seven countries (Switzerland, Netherlands, Germany, United Kingdom, United States, Israel, and Japan).

MAIN OUTCOME MEASURES

Mean effective doses and proportions of high dose examinations for abdomen, chest, combined chest and abdomen, and head CT were determined by patient characteristics (sex, age, and size), type of institution (trauma center, care provision 24 hours per day and seven days per week, academic, private), institutional practice volume, machine factors (manufacturer, model), country, and how scanners were used, before and after adjustment for patient characteristics, using hierarchical linear and logistic regression. High dose examinations were defined as CT scans with doses above the 75th percentile defined during a baseline period.

RESULTS

The mean effective dose and proportion of high dose examinations varied substantially across institutions. The doses varied modestly (10-30%) by type of institution and machine characteristics after adjusting for patient characteristics. By contrast, even after adjusting for patient characteristics, wide variations in radiation doses across countries persisted, with a fourfold range in mean effective dose for abdomen CT examinations (7.0-25.7 mSv) and a 17-fold range in proportion of high dose examinations (4-69%). Similar variation across countries was observed for chest (mean effective dose 1.7-6.4 mSv, proportion of high dose examinations 1-26%) and combined chest and abdomen CT (10.0-37.9 mSv, 2-78%). Doses for head CT varied less (1.4-1.9 mSv, 8-27%). In multivariable models, the dose variation across countries was primarily attributable to institutional decisions regarding technical parameters (that is, how the scanners were used).

CONCLUSIONS

CT protocols and radiation doses vary greatly across countries and are primarily attributable to local choices regarding technical parameters, rather than patient, institution, or machine characteristics. These findings suggest that the optimization of doses to a consistent standard should be possible.

STUDY REGISTRATION

Clinicaltrials.gov NCT03000751.

Cone beam computed tomography-guided thin/ultrathin bronchoscopy for diagnosis of peripheral lung nodules: a prospective pilot study

Background

Despite advances in bronchoscopy, its diagnostic yield for peripheral lung lesions continues to be suboptimal. Cone beam computed tomography (CBCT) could be utilized to corroborate the accuracy of our bronchoscopic navigation and hopefully increase its diagnostic yield. However, data on radiation exposure and feasibility of CBCT-guided bronchoscopy is scarce.

Methods

Prospective pilot study of bronchoscopy for peripheral lung nodules under general anesthesia with thin/ultrathin bronchoscope, radial-probe endobronchial ultrasound (RP-EBUS), and CBCT. Main objective was to estimate radiation dose and secondary objective was the additional value of CBCT in terms of navigational and diagnostic yield.

Results

A total of 20 patients were enrolled. Median lesion size was 2.1 (range, 1.1-3) cm and distance from pleura was 2.1 (range, 0-2.8) cm. "Bronchus sign" was present in 12 (60%) of the lesions. Totally, 12 lesions (60%) were invisible on fluoroscopy. CBCT identified atelectasis obscuring the target in 4 cases (20%). Eleven patients (55%) underwent 1 CBCT scan and 9 patients (45%) 2. The mean estimated effective dose (E) to patients resulting from CBCT ranged between 8.6 and 23 mSv, depending on utilized conversion factors. Both pre-CBCT navigation and diagnostic yield were 50%. Additional post-CBCT maneuvers increased navigation yield to 75% (P=0.02) and diagnostic yield to 70% (P=0.04). One patient developed a pneumothorax.

Conclusions

CBCT-guided bronchoscopy is associated with an acceptable radiation dose. CBCT may potentially increase both navigation and diagnostic yield of thin/ultrathin bronchoscopy for peripheral lung nodules. The above findings as well as the incidental but relevant finding of intra-procedural atelectasis need to be confirmed in larger prospective studies.

Trial registration

This study is registered in ClinicalTrials.gov as number NCT02978170.