Non-invasive assessment of response to transcatheter arterial chemoembolization for hepatocellular carcinoma with the deep neural networks-based radiomics nomogram.

BACKGROUND: Transcatheter arterial chemoembolization (TACE) is a mainstay treatment for intermediate and advanced hepatocellular carcinoma (HCC), with the potential to enhance patient survival. Preoperative prediction of postoperative response to TACE in patients with HCC is crucial. PURPOSE: To develop a deep neural network (DNN)-based nomogram for the non-invasive and precise prediction of TACE response in patients with HCC. MATERIAL AND METHODS: We retrospectively collected clinical and imaging data from 110 patients with HCC who underwent TACE surgery. Radiomics features were extracted from specific imaging methods. We employed conventional machine-learning algorithms and a DNN-based model to construct predictive probabilities (RScore). Logistic regression helped identify independent clinical risk factors, which were integrated with RScore to create a nomogram. We evaluated diagnostic performance using various metrics. RESULTS: Among the radiomics models, the DNN_LASSO-based one demonstrated the highest predictive accuracy (area under the curve [AUC] = 0.847, sensitivity = 0.892, specificity = 0.791). Peritumoral enhancement and alkaline phosphatase were identified as independent risk factors. Combining RScore with these clinical factors, a DNN-based nomogram exhibited superior predictive performance (AUC = 0.871, sensitivity = 0.844, specificity = 0.873). CONCLUSION: In this study, we successfully developed a deep learning-based nomogram that can noninvasively and accurately predict TACE response in patients with HCC, offering significant potential for improving the clinical management of HCC.

Visualization and comparison of CT dose distribution between axial and helical acquisitions.

BACKGROUND: It is challenging to assess the accuracy of volume CT Dose Index (CTDIvol ) when the axial scan modes corresponding to a helical scan protocol are not available. An alternative approach was proposed to directly measure C T D I v o l H $CTDI_{vol}^H$ using helical acquisitions and relatively small differences (< 20%) from CTDIvol were observed. PURPOSE: To visually demonstrate the 3D dose distribution for both axial and helical CT acquisitions and quantitively compare C T D I v o l H $CTDI_{vol}^H$ and CTDIvol . METHODS: 3D dose distribution within the standard CTDI phantoms (16 and 32 cm diameter) from a single CT projection, Dp (x,y,z) was first generated using Monte Carlo simulation (GEANT4) with 9×108 photons per combination of tube voltage (80-140 kV), collimation width (1-8 cm), and z-axis location of the central ray of the x-ray beam, with a spatial resolution of 1 mm3 . These dose distributions from one single projection were analytically ensembled to simulate 3D dose volumes DA (x,y,z) and DH (x,y,z) for axial and helical scans, respectively, with different helical pitches (0.3-2) and scan lengths (100-150 mm). 2D planar dose distributions were obtained by integrating the inside 100 mm of the dose volumes. CTDIvol and C T D I v o l H $CTDI_{vol}^H\;$ were calculated using the planar dose data at corresponding pencil chamber locations and the percentage differences (PD) were reported. RESULTS: High spatial resolution 3D CT dose volumes were generated and visualized. PDs between C T D I v o l H $CTDI_{vol}^H$ and CTDIvol had strong dependency on scan length and peripheral chamber locations, with subtle dependency on collimation width and pitch. PDs were mostly within the range of ± 3% for a scan length of 150 mm with four peripheral chamber locations. CONCLUSIONS: With a scan length covering the entire phantom length, C T D I v o l H $CTDI_{vol}^H$ directly measured from helical scans can serve as an alternative to CTDIvol only if all four peripheral locations were measured.

Calculation of scan length and size-specific dose at longitudinal positions of body CT scans using dose equilibrium function.

BACKGROUND: Dose evaluation at longitudinal positions of body computed tomography (CT) scans is useful for CT quality assurance programs and patient organ dose evaluation. Accurate estimates depend on both patient size and scan length. PURPOSE: To propose practical evaluation of the average dose to the transverse slab of an axial image slice for adult body CT examinations, considering not only patient size but also scan length, and to compare the results with those of Monte Carlo (Geant4) simulation [Dsim (z)] and size-specific dose estimates at longitudinal positions of scans [SSDE(z)] from international standards (IEC publication no. 62985). METHODS: In a scan series, the total dose at each z-axis location was calculated using the input information identical to the SSDE(z) evaluation. Each axial image slice (slice thickness, 2.5 or 5 mm) was first considered independently. Its z-axis coverage and CTDIvol (from the DICOM headers) were used to directly calculate a z-axis dose profile for the average dose over the cross-section of a water phantom, using the approach to equilibrium function. The phantom diameter was taken to be equal to the patient water equivalent diameter at that slice. The above was repeated at all slices and the dose at each z-axis location was accumulated from all profiles, referred to as Dcalc (z). For validation, we considered a cohort of 65 patients, who underwent chest and abdominopelvic examinations. The resultant Dcalc (z) was compared with Dsim (z) and SSDE(z), both available in a previous paper. RESULTS: Dcalc (z) evaluation could be used to accurately assess the scan range average dose, with an accuracy of 7.1%-8.7% for 65 patients in two examinations. On individual image slices, the maximum difference in magnitude between Dcalc (z) and Dsim (z) [and between SSDE(z) and Dsim (z) in parentheses] was 37.5% (85%) [two edges (2 × 5 cm) of chest scan range], 17.8% (35.2%) (the remaining central region of chest scan), 26.8% (74.1%) [two edges (2 × 5 cm) of abdominopelvic scan range], and 14.2% (22.5%) (the remaining central region of abdominopelvic scan). CONCLUSIONS: Identical input data are used for Dcalc (z) and SSDE(z) evaluations. The latter is limited to the z-axis locations within scan range. At each image slice, SSDE(z) is equivalent to the midpoint dose of a fixed-mA scan of 15-30 cm (scan length). In contrast, Dcalc (z) considers dose accumulation from varying scan length (from sub-centimeter to about 1 m) and tube current, and dose profile is also computed outside scan range. Besides greatly improving dose evaluation for individual image slices, Dcalc (z) allows for evaluating dose accumulation from multiple series, which typically span different scan ranges. Our proposal may assist CT manufacturers and dose index monitoring software in assessing dose at longitudinal positions of body CT scans.

Patients undergoing multiple 18F-FDG PET/CT exams: Assessment of frequency, dose and disease classification.

OBJECTIVE: To analyse the frequency, demographics, primary disease and cumulative effective dose of patients undergoing two or more 18F-FDG PET/CT examinations in a year. METHODS: In a retrospective study performed at a tertiary-care hospital, patients who underwent ≥2 18F-FDG PET/CT scans in a calendar year were identified for two consecutive years. The CT radiation dose was calculated using dose-length-product and sex-specific conversion factors. The primary malignancy of patients was retrieved from electronic medical records. RESULTS: 10,714 18F-FDG PET/CT exams were performed for 6,831 unique patients in 2 years, yielding an average of 1.6 exams per patient. The maximum number of 18F-FDG PET/CT examinations any patient underwent in a single year was seven. 20.9% patients had ≥2 18F-FDG PET/CT exams in any single year. Thirty nine percent patients in the cohort were below 60 years age. The median dose for 18F-FDG PET/CT examination was 25.1 mSv and maximum value reaching 1.7 to 2.9 times the median value. Cumulative effective dose (CED) was≥100 mSv in 12-13% of the patients. The cumulative dose for both years combined demonstrated the 25th percentile, 50th percentile and 75th percentile as well as the mean to be over 100 mSv, with the 25th percentile being 109 mSv. The dominant primary malignancies contributing to serial 18F-FDG PET/CTs in decreasing frequency were melanoma, non-Hodgkin's lymphoma (NHL), gastrointestinal cancer, breast cancer and Hodgkin's lymphoma. CONCLUSIONS: A sizeable number of patients undergo≥2 18F-FDG PET/CT exams with one out of every eight patients receiving cumulative dose≥100 mSv and that includes patients with long-life expectancy. ADVANCES IN KNOWLEDGE: The study found that one of five patients had≥2 18F-FDG PET/CT exams in a calendar year, one of four patients in two years and one of eight patients received cumulative dose≥100 mSv. Top malignancies associated with serial imaging in decreasing order of frequency included melanoma, non-Hodgkin's lymphoma (NHL), gastrointestinal cancer, breast cancer and Hodgkin's lymphoma.

Technical note: Advancing size-specific dose estimates in CT examinations: Dose estimates at longitudinal positions of scans.

PURPOSE: American Association of Physicists in Medicine (AAPM) (Report 204) introduced the size-specific dose estimate (SSDE) for the average dose to the center of a fixed-mA scan. International standards establish a method that CT manufacturers and radiation dose index monitoring software may use to calculate SSDE(z) at longitudinal positions of scans with fixed mA or tube current modulation, and its scan range average SSDE ( z ) ¯ $\overline {{\rm{SSDE}}( z )} $ . We sought to test how accurate SSDE(z) is in tracking the average dose to the transverse slab of an axial image slice (Dslice ), evaluated with Monte Carlo calculation, in the chest and abdominopelvic examinations. METHODS: We retrospectively identified 65 consecutive adult patients undergoing whole-body CT for transcatheter aortic valve implantation planning. Examination parameters (kV, mA, CTDIvol ) were extracted from the DICOM headers. Patient water equivalent diameter DW (z) was calculated at each image slice, excluding the patient table. A previously validated Monte Carlo simulation (Geant4) program was used to evaluate Dslice from the chest and abdominopelvic examinations. Alternatively, SSDE(z) was calculated at each slice. The results of the two methods were compared with descriptive statistical outcomes (R, version 4.0.2). RESULTS: In chest and abdominopelvic CT examinations, Dslice largely changed with anatomic location and uniformly fell off toward scan range edges. Scan range averages SSDE ( z ) ¯ $\overline {{\rm{SSDE}}( z )} $ and D slice ¯ $\overline {{D_{{\rm{slice}}}}} \;$ were consistent within 2.5%-3.1% (median) and 6.3%-10.4% (maximum) in two examinations. On individual image slices, SSDE(z) could be lower or higher than Dslice , with deviation ranging from -18.3% to 85% in two edges (2 × 5 cm) of scan range and from -35.2% to 18.7% in the remaining central region of the scan. CONCLUSION: This study provides critical inputs for quality assurance programs. SSDE ( z ) ¯ $\overline {{\rm{SSDE}}( z )} $ is useful to track the average dose of all image slices, but further development may be useful for tracking patient dose at the level of individual image slices, especially near a scan range edge.

Fetal dose evaluation for body CT examinations of pregnant patients during all stages of pregnancy.

PURPOSE: CTDIvol-to-fetal-dose coefficients from Monte Carlo simulations are useful for fetal dose evaluations, but the available data is limited to the fetus being completely inside the abdominopelvic scan range. Whereas in a chest examination, the fetus is completely outside the scan range. In an abdominal examination, the fetus after 16 gestational weeks is partly in the scan region, and an earlier fetus is completely outside of it. This work proposes a practical approach to evaluate fetal dose for pregnant patients undergoing body CT examinations, without using Monte Carlo simulation. METHODS: The proposed method was based on the z-axis dose profile computed for a CT examination, considering CTDIvol, scan range, mA, and maternal WED (water equivalent diameter) at the fetus centroid. Fetal average dose was calculated over the fetus z-axis coverage. For validation, we considered a reference dataset of 24 pregnant patients, each underwent two abdominopelvic examinations (fixed mA, tube current modulation). WED was 30.1 ± 3.3 (25.3-35.6) cm [mean(range)]. Gestational age was <5 weeks for one patient, and 20.3 ± 9.1 (5-35.9) weeks for the others. Fetal depth (from the anterior skin surface to the most anterior part of fetus) was 6.1 ± 2.1 (2.5-10.9) cm. We further considered three whole-body models of a pregnant patient (gestational age, 3, 6, 9 months; weight, 62-73 kg) undergoing chest, abdominal, and abdominopelvic examinations (fixed mA). For the patients and models, profile-based fetal dose calculations were compared with the results of Monte Carlo simulations. Statistical software (R, version 3.5.1) was used to determine the mean and 95th percentile. RESULTS: The fetal dose difference between profile-based evaluations and Monte Carlo simulations was (5.9 ± 3.8)% for 24 fixed-mA examinations, (5.8 ± 4.6)% for 24 tube current modulated examinations, and (8.8 ± 5.9)% for the whole-body models in three scan ranges. CONCLUSIONS: Profile-based fetal dose calculations can be performed for patients in body CT, considering maternal size, fetus size and location, and whether fetus is completely inside, partly inside, or outside scan ranges.

Experimental and numerical studies on kV scattered x-ray imaging for real-time image guidance in radiation therapy.

Motion management is a critical component of image guided radiotherapy for lung cancer. We previously proposed a scheme using kV scattered x-ray photons for marker-less real-time image guidance in lung cancer radiotherapy. This study reports our recent progress using the photon counting detection technique to demonstrate potential feasibility of this method and using Monte Carlo (MC) simulations and ray-tracing calculations to characterize the performance. In our scheme, a thin slice of x-ray beam was directed to the target and we measured the outgoing scattered photons using a photon counting detector with a parallel-hole collimator to establish the correspondence between detector pixels and scatter positions. Image corrections of geometry, beam attenuation and scattering angle were performed to convert the raw image to the actual image of Compton attenuation coefficient. We set up a MC simulation system using an in-house developed GPU-based MC package modeling the image formation process. We also performed ray-tracing calculations to investigate the impacts of imaging system geometry on resulting image resolution. The experiment demonstrated feasibility of using a photon counting detector to measure scattered x-ray photons and generate the proposed scattered x-ray image. After correction, x-ray scattering image intensity and Compton scattering attenuation coefficient were linearly related, with R 2 greater than 0.9. Contrast to noise ratios of different objects were improved and the values in experimental results and MC simulation results agreed with each other. Ray-tracing calculations revealed the dependence of image resolution on imaging geometry. The image resolution increases with reduced source to object distance and increased collimator height. The study demonstrated potential feasibility of using scattered x-ray imaging as a real-time image guidance method in radiation therapy.

E-cigarette use among adults in China: findings from repeated cross-sectional surveys in 2015-16 and 2018-19.

BACKGROUND: The use of e-cigarettes among adults is increasing globally. Since 2018, policies in China have restricted e-cigarette use; however, little information is available on the national trend in e-cigarette use before regulations were implemented. Therefore, we sought to estimate the trend in e-cigarette use in China before policy implementation and explored associated factors. METHODS: We assessed two nationally representative cross-sectional datasets from the China Chronic Disease and Nutrition Surveillance (CCDNS) surveys initiated in 2015 (June, 2015, to May, 2016) and 2018 (August, 2018, to June, 2019). The surveys were done at 298 national disease surveillance points in 31 provinces in mainland China, and used a multistage, stratified, cluster-randomised sampling design, recruiting community-based Chinese adults aged 18 years and older. Within the standard CCDNS survey, face-to-face questionnaire interviews were used to collect self-report data on e-cigarette use in the preceding 30 days. E-cigarette users were those who self-reported e-cigarette use on 1 day or more in the past 30 days. Prevalence estimates of past 30-day e-cigarette use were weighted to represent the Chinese adult population accounting for the complex sampling design. Populations for the years 2015-16 and 2018-19 were standardised with the 2010 population census to gain comparable estimates. Multivariable logistic regression models adjusted for age, sex, urban or rural residence, household income, occupation, and education level were applied to identify factors associated with the likelihood of e-cigarette use among the total population, ever smokers (current and former), and never smokers across both surveys. FINDINGS: Our study included 189 306 Chinese adults from the 2015 survey (100 405 [53·0%] women; mean age 43·6 years [SD 14·6]) and 184 475 Chinese adults from the 2018 survey (102 373 [55·5%] women; mean age 43·4 years [13·9]). The weighted prevalence of past 30-day e-cigarette use among Chinese adults increased from 1·3% (95% CI 1·1-1·5%) in 2015-16 to 1·6% (95% CI 1·4-1·8%) in 2018-19 (an increase of 0·3% [95% CI 0·1-0·6]; Rao-Scott χ2 p=0·0086). Based on weighted proportion data, e-cigarette users were predominantly men (97·4% [95% CI 96·7-98·1] in 2015-16 and 97·0% [95·4-98·6] in 2018-19) and current conventional smokers (93·0% [90·7-95·2] in 2015-16 and 96·2% [95·1-97·3] in 2018-19). Across both surveys, the odds of e-cigarette use were significantly associated with obesity (odds ratio 1·6 [95% CI 1·3-2·1]; p=0·0007), awareness of smoking hazards (1·2 [1·0-1·4]; p=0·022), and smoking status (in current smokers, 135·2 [87·7-208·6]; and in former smokers, 33·5 [21·3-52·7]; p<0·0001). Among current smokers, the odds were increased with daily cigarette consumption (2·1 [1·5-2·8]; p<0·0001), smoking more than 20 cigarettes per day (1·8 [1·5-2·3]; p<0·0001), and an attempt to quit smoking (within the past 12 months, 1·9 [1·5-2·4]; and before the past 12 months, 1·5 [1·3-1·9]; p<0·0001). In never smokers, the odds were increased in those aware of the hazards of smoking (2·4 [1·2-4·7]; p=0·011). INTERPRETATION: E-cigarette use in China remains low but has increased substantially between 2015 and 2019. Our study identified increased e-cigarette use among subpopulations, and use patterns, that warrant further attention from public health policy makers in China. FUNDING: Chinese Central Government, National Key Research and Development Program of China.

Reducing Salt Intake in China with "Action on Salt China" (ASC): Protocol for Campaigns and Randomized Controlled Trials.

BACKGROUND: Salt intake in China is over twice the maximum recommendation of the World Health Organization. Unlike most developed countries where salt intake is mainly derived from prepackaged foods, around 80% of the salt consumed in China is added during cooking. OBJECTIVE: Action on Salt China (ASC), initiated in 2017, aims to develop, implement, and evaluate a comprehensive and tailored salt reduction program for national scaling-up. METHODS: ASC consists of six programs working in synergy to increase salt awareness and to reduce the amount of salt used during cooking at home and in restaurants, as well as in processed foods. Since September 2018, two health campaigns on health education and processed foods have respectively started, in parallel with four open-label cluster randomized controlled trials (RCTs) in six provinces across China: (1) app-based intervention study (AIS), in which a mobile app is used to achieve and sustain salt reduction in school children and their families; (2) home cook-based intervention study (HIS), in which family cooks receive support in using less salt; (3) restaurant-based intervention study (RIS) targeting restaurant consumers, cooks, and managers; and (4) comprehensive intervention study (CIS), which is a real-world implementation and evaluation of all available interventions in the three other RCTs. To explore the barriers, facilitators, and effectiveness of delivering a comprehensive salt reduction intervention, these RCTs will last for 1 year (stage 1), followed by nationwide implementation (stage 2). In AIS, HIS, and CIS, the primary outcome of salt reduction will be evaluated by 24-hour urinary sodium excretion in 6030 participants, including 5436 adults and 594 school children around 8-9 years old. In RIS, the salt content of meals will be measured by laboratory food analysis of the 5 best-selling dishes from 192 restaurants. Secondary outcomes will include process evaluation; changes in knowledge, attitude, and practice on salt intake; and economic evaluation. RESULTS: All RCTs have been approved by Queen Mary Research Ethics Committee and the Institutional Review Boards of leading institutes in China. The research started in June 2017 and is expected to be completed around March 2021. The baseline investigations of the four RCTs were completed in May 2019. CONCLUSIONS: The ASC project is progressing smoothly. The intervention packages and tailored components will be promoted for salt reduction in China, and could be adopted by other countries. TRIAL REGISTRATION: Chinese Clinical Trial Registry. AIS: ChiCTR1800017553; https://tinyurl.com/vdr8rpr. HIS: ChiCTR1800016804; https://tinyurl.com/w8c7x3w. RIS: ChiCTR1800019694; https://tinyurl.com/uqkjgfw. CIS: ChiCTR1800018119; https://tinyurl.com/s3ajldw. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/15933.

Quantitative evaluation of transmission properties of breast tissue equivalent materials under Compton scatter imaging setup.

To explore the potential of utilizing Compton scattered x-ray photons for imaging applications, it is critical to accurately evaluate scattered x-ray transmission properties of targeted tissue materials. In this study, scattered x-ray transmission of breast tissue equivalent phantoms was evaluated. Firstly, two validations were carried out using a primary x-ray beam at 80 kVp with both experimental measurement (ion chamber with narrow-beam setup) and analytical calculation (Spektr toolkit). The tungsten-anode x-ray spectrum model was thus validated by measuring and calculating the transmission through increasing thickness of 1100 Aluminum filters. Similarly, the composition models of breast tissue equivalent phantoms (CIRS, 012A) were validated by measuring and calculating x-ray transmission for three different breast compositions (BR30/70, BR50/50, and BR70/30). Following validation, transmission properties of Compton scattered x-ray photons were measured with a GOS based linear array detector at the 90° angle from the primary beam. The same study was performed through three independent approaches: experimental measurement, analytical calculation, and Monte Carlo simulation (GEANT4). For all three methods, the scattered x-ray photon transmission as functions of phantom thickness were determined and fit into exponential functions. The transmission curves from all three methods matched reasonably well, with a maximum difference of 6.3% for the estimated effective attenuation coefficients of the BR50/50 phantom. The relative difference among the three methods of estimated attenuation is under 3.5%. As an initial step to develop a novel Compton scatter-based breast imaging system, the quantitative results from this study paved a fundamental base for future work.

Geographical variations in cardiovascular health in China: A nationwide population-based survey of 74,726 adults.

BACKGROUND: Cardiovascular disease is the leading cause of death in China. The aim of this study was to evaluate the levels of cardiovascular health among Chinese adults and to understand the geographic pattern of cardiovascular health. METHODS: In 2015, a total of 74,726 respondents aged ≥ 20 years with no history of cardiovascular disease were randomly sampled from 298 counties/districts of 31 provinces in mainland China and were interviewed. Seven metrics, including smoking, body mass index, physical activity, diet, total cholesterol, blood pressure, and fasting glucose, were determined. Ideal cardiovascular health was defined as the simultaneous presence of all metrics at the ideal level. A score ranging from 0 to 14 was calculated as the sum of all seven metrics for each province. Scores for cardiovascular health behaviors (smoking, body mass index, physical activity and diet) and those for cardiovascular health factors (smoking, total cholesterol, blood pressure, and fasting glucose) were also calculated. FINDINGS: The mean age was 44.4 ± 15.9 years, and 49.3% were women. The age-sex-standardized prevalence of ideal cardiovascular health was universally poor, ranging from 0.02% [95% confidence interval (CI): 0%, 0.05%] in Tibet to 2.76% (95% CI: 0.45%, 5.07%) in Heilongjiang. Ideal diet (7.1%) was the least common factor of the seven metrics in each province and varied considerably across provinces. Other component metrics of ideal cardiovascular health were also spatially patterned. In all provinces, women had higher scores than men for cardiovascular health, health behaviors and health factors. Differences in cardiovascular health and health behavior scores between urban and rural areas were associated with levels of socio-economic development. INTERPRETATION: Strategies for addressing poor cardiovascular health require geographic targeting and localized consideration. FUNDING: This research was supported by National Key R&D Program, the Shenzhen Strategic Emerging Industry Development Special Fund, and the Fund of "Sanming" Project of Medicine in Shenzhen.

Effective Dose Assessment for Patients Undergoing Contemporary Fluoroscopically Guided Interventional Procedures.

OBJECTIVE. The purpose of this study was to establish procedure-specific air kerma-area product (KAP) and effective dose for a large number of fluoroscopically guided interventional (FGI) procedures. MATERIALS AND METHODS. This retrospective study collected dose data for consecutive adult cases from 12 examination rooms between May 2016 and October 2018. A total of 24,911 cases (50.9% men) were categorized by procedure. Effective dose was calculated using KAP and procedure-specific KAP to effective dose conversion coefficients, mostly from National Council on Radiation Protection and Measurements (NCRP) Report 160. Data analysis was conducted with statistical software to determine mean value and five percentiles (10th, 25th, 50th, 75th, 95th). RESULTS. KAP and effective dose were presented for 101 procedures; a national benchmark is not available from NCRP Reports 168 and 172 for the KAP value of 89 procedures and for the effective dose of all 101 procedures. Twelve procedures that comprised at least 50% of patient cases had median KAP values less than 3.26 Gy · cm2 and a median effective dose of less than 0.70 mSv. However, some infrequent procedures might be associated with a higher dose. The 95th percentile of KAP was greater than or equal to 500 Gy · cm2 for 16 procedures and 985 Gy · cm2 for portography; for effective dose it was greater than or equal to 100 mSv for 21 procedures and 256 mSv for portography. CONCLUSION. The values for KAP and effective dose provided in this article can aid in design and review of clinical research protocols and dose management programs and in assessing compliance with the Joint Commission's standards for organizations providing fluoroscopy services in the absence of national benchmarks for more than 89 procedures.

Exam-level dose monitoring in CT: Quality metric consideration for multiple series acquisitions.

PURPOSE: Multi-series CT examination is common in the clinic, but no metric is agreed upon to report the overall dose from such an examination. This work proposes a relevant metric for tracking patient dose from multi-series examinations and illustrates the evaluation method through explanatory examples. MATERIALS AND METHODS: In each acquisition series, a previously reported method was used to evaluate the cross-sectional average dose along the z-axis of a water phantom, with inputs of CTDIvol , scan length, tube current, and patient water-equivalent diameter. With a multi-series examination, the dose at each z-location was accumulated over all acquisition series. This method was applied to four clinical CT examinations. In three abdominal/pelvic examinations (patient weight, 107, 79, 79 kg), tube current modulation was applied in five acquisition series with scan lengths of 30-41.8 cm, while tube current was fixed in other series with short scan lengths (1.0, 7.9 cm). In another CT-guided liver ablation procedure (patient weight, 114 kg), 22 series were acquired with constant mA and scan lengths of 1-30 cm. The maximum value of the overall dose profile of each examination was compared to five dose quantities, including CTDIvol,sum and SSDEsum by the ACR CT Dose Index Registry, scan length-weighted CTDIvol and SSDE by a CT dose monitoring platform, and "max z location CTDIvol " by a CT manufacturer. RESULTS: A simple graphic display of dose as a function of the z-axis location was presented for each acquisition series and for the whole examination. Differences up to 43.4% and 42.8%, or down to -93.5%, -93.5%, and -49.0%, were observed between the maximum value of the overall dose profile and five dose quantities (in the above order), respectively. CONCLUSION: The overall dose profile gives a complete description of z-axis dose distribution for the studied CT examinations under a wide range of patient variables and acquisition conditions, including multiple acquisition series. Simple visualization of the doses across and beyond the scan ranges may provide a new tool for CT dose optimization.

Assessment of radiation dose from abdominal quantitative CT with short scan length.

OBJECTIVE: To assess radiation dose for patients who received abdominal quantitative CT and to compare the midpoint dose [DL(0)] at the centre of a 1-cm scan length with the volume CT dose index (CTDIvol). Although the size-specific dose estimate (SSDE) proposed in The American Association of Physicists in Medicine Report No. 204 is not applicable for short-length scans, commercial dose-monitoring software, such as Radimetrics™ Enterprise Platform (Bayer HealthCare, Whippany, NJ), reports SSDE for all scans. SSDE was herein compared with DL(0). METHODS: Data were analyzed from 398 abdominal quantitative CT examinations in 165 males and 233 females. The CTDIvol was 4.66 mGy, and the scan length was 1 cm for all examinations. Radimetrics was used to extract patient diameter and SSDE. DL(0) was assessed using a previously reported method that takes into account both patient size and scan length. RESULTS: The mean patient diameter was 28.5 ± 6.3 cm (range, 16.5-46.6 cm); the mean SSDE was 6.22 ± 1.36 mGy (range, 3.12-9.42 mGy); and the mean DL(0) was 2.97 ± 0.95 mGy (range, 1.18-5.77 mGy). As patient diameter increased, the DL(0) to CTDIvol ratio decreased, ranging from 1.24 to 0.25; the DL(0) to SSDE ratio also decreased, ranging from 0.61 to 0.38. CONCLUSION: The dose to the patients from abdominal quantitative CT may be largely different from CTDIvol and SSDE. This study demonstrates the necessity of taking into account not only patient size but also scan length for evaluating the dose from short-length scans. Advances in knowledge: In CT examinations with 1-cm scan length, dose evaluation needs to take into account both patient size and scan length. An omission of either factor can result in an erroneous result.

Direct and fast measurement of CT beam filter profiles with simultaneous geometrical calibration.

PURPOSE: To accurately measure the beam filter profiles from a variety of CT scanner models and to provide reference data for Monte Carlo simulations of CT scanners. METHODS: This study proposed a new method to measure CT beam filter profiles using a linear-array x-ray detector (X-Scan 0.8f3-512; Detection Technology Inc., Espoo, Finland) under gantry rotation mode. A robust geometrical calibration approach was developed to determine key geometrical parameters by considering the x-ray focal spot location relative to the linear-array detector and the gantry's angular increment at each acquisition point. CT beam intensity profiles were synthesized from continuously measured data during a 10° gantry rotation range with calibrated detector response and system geometry information. Relative transmission profiles of nineteen sets of beam filters were then derived for nine different CT scanner models from three different manufacturers. Equivalent aluminum thickness profiles of these beam filters were determined by analytical calculation using the Spektr Matlab software package to match the measured transmission profiles. Three experiments were performed to validate the accuracy of the geometrical calibration, detector response modeling, and the derived equivalent aluminum thickness profiles. RESULTS: The beam intensity profiles measured from gantry rotation mode showed very good agreement with those measured with gantry stationary mode, with a maximal difference of 3%. The equivalent aluminum thickness determined by this proposed method agreed well with what was measured by an ion chamber, with a mean difference of 0.4%. The determined HVL profiles matched well with data from a previous study (max difference of 4.7%). CONCLUSIONS: An accurate and robust method to directly measure profiles from a broad list of beam filters and CT scanner models was developed, implemented, and validated. Useful reference data was provided for future research on CT system modeling.

A study of the midpoint dose to CTDIvol ratio: Implications for CT dose evaluation.

PURPOSE: In multidetector CT, the volume CT dose index (CTDIvol) is reported for each scan series and dose conversion factors are used for the size-specific dose estimate (SSDE) and scanner-independent organ dose evaluation. This study aimed at examining the dependencies of conversion factors on scan length, tube voltage, and subject size. The results may be insightful for evaluating the dose from CT examinations with large variations in patient size and scan length. METHODS: A previously developed Monte Carlo simulation program was used to simulate single rotation axial scans of two standard CTDI phantoms [material polymethyl methacrylate (PMMA), diameters 16 and 32 cm] and multiple water cylinders at five tube voltages (70, 80, 100, 120, and 140 kV). The resultant longitudinal dose profiles were used to calculate CTDIL(water)/CTDIw (PMMA), where L was dose integration length. The ratio was equal to the midpoint dose DL(0) (water) to CTDIvol ratio in a CT scan series with a scan length equal to L. RESULTS: For water phantom diameters from 11 to 50 cm and scan lengths from 15 to 30 cm, the changes of DL(0)/CTDIvol from that of 120 kV and 20-cm scan length were between -18.4% and 11.7%. This was consistent with the CTDIvol to SSDE conversion factors of AAPM Report No. 204. For scan lengths less than 15 cm, DL(0)/CTDIvol decreased considerably as L decreased. DL(0)/CTDIvol was shown to be 17.3%-31.4% lower for L = 5 cm than for L = 15 cm, when the tube voltage was 120 kV and phantom diameter ranged from 11 to 50 cm. As tube voltage increased from 80 to 140 kV, DL(0)/CTDIvol decreased at small diameters while it increased at large diameters. The change was 9.4% with a diameter of 18 cm and a scan length of 20 cm and 17.6% with a diameter of 40 cm and a scan length of 30 cm. CONCLUSIONS: The midpoint dose to CTDIvol ratio varies widely across the clinical scan lengths from a few millimeters to about 1 m and varies moderately across tube voltages from 70 to 140 kV. The comprehensive data provided in the Appendix can be used for assessing the dose from short-length scans and improving the dose evaluation in CT.

CT dose equilibration and energy absorption in polyethylene cylinders with diameters from 6 to 55 cm.

PURPOSE: ICRU Report No. 87 Committee and AAPM Task Group 200 designed a three-sectional polyethylene phantom of 30 cm in diameter and 60 cm in length for evaluating the midpoint dose DL(0) and its rise-to-the-equilibrium curve H(L) = DL(0)/D(eq) from computed tomography (CT) scanning, where D(eq) is the equilibrium dose. To aid the use of the phantom in radiation dose assessment and to gain an understanding of dose equilibration and energy absorption in polyethylene, the authors evaluated the short (20 cm) to long (60 cm) phantom dose ratio with a polyethylene diameter of 30 cm, assessed H(L) in polyethylene cylinders of 6-55 cm in diameters, and examined energy absorption in these cylinders. METHODS: A GEANT4-based Monte Carlo program was used to simulate the single axial scans of polyethylene cylinders (diameters 6-55 cm and length 90 cm, as well as diameter 30 cm and lengths 20 and 60 cm) on a clinical CT scanner (Somatom Definition dual source CT, Siemens Healthcare). Axial dose distributions were computed on the phantom central and peripheral axes. An average dose over the central 23 or 100 mm region was evaluated for modeling dose measurement using a 0.6 cm(3) thimble chamber or a 10 cm long pencil ion chamber, respectively. The short (20 cm) to long (90 cm) phantom dose ratios were calculated for the 30 cm diameter polyethylene phantoms scanned at four tube voltages (80-140 kV) and a range of beam apertures (1-25 cm). H(L) was evaluated using the dose integrals computed with the 90 cm long phantoms. The resultant H(L) data were subsequently used to compute the fraction of the total energy absorbed inside or outside the scan range (E(in)/E or E(out)/E) on the phantom central and peripheral axes, where E = LD(eq) was the total energy absorbed along the z axis. RESULTS: The midpoint dose in the 60 cm long polyethylene phantom was equal to that in the 90 cm long polyethylene phantom. The short-to-long phantom dose ratios changed with beam aperture and phantom axis but were insensitive to tube voltage. H(L) was insensitive to tube voltage and CT scanner model. As phantom diameter increased from 6 to 55 cm, E(in)/E generally decreased but asymptotically approached constant levels on the peripheral axes of large phantoms. The curve of E(in)/E versus scan length was almost identical to that of H(L). Similarly, E(out)/E increased with scan length and asymptotically approached the equilibrium for large scan lengths. E(out)/D(eq) was much less than the equilibrium length L(eq) where H(L) = 0.98, even with scan lengths much larger than L(eq). CONCLUSIONS: The polyethylene phantom designed by ICRU Report No. 87 Committee and AAPM Task Group 200 is adequately long for assessing the midpoint dose and its equilibration in CT scanning. The short-to-long phantom dose ratios and the H(L) data provided in this paper allow easy evaluations of the midpoint dose, longitudinal dose distribution, and energy absorption in polyethylene phantoms. The results of dose equilibration and energy absorption presented herein may be insightful for the clinical CT scans with various subject sizes and scan lengths.