Cumulative radiation exposure from multimodality recurrent imaging of CT, fluoroscopically guided intervention, and nuclear medicine.

OBJECTIVES: To assess cumulative effective dose (CED) over a 4-year period in patients undergoing multimodality recurrent imaging at a major hospital in the USA. METHODS: CED from CT, fluoroscopically guided intervention (FGI), and nuclear medicine was analyzed in consecutive exams in a tertiary care center in 2018-2021. Patients with CED ≥ 100 mSv were classified by age and body habitus (underweight, healthy weight, overweight, obese), as per body mass index percentiles < 5th, 5th to < 85th, 85th to < 95th, and ≥ 95th (age 2-19 years), and its ranges < 18.5, 18.5-24.9, 25-29.9, and ≥ 30 (≥ 20 years), respectively. RESULTS: Among a total of 205,425 patients, 5.7% received CED ≥ 100 mSv (mean 184 mSv, maximum 1165 mSv) and their ages were mostly 50-64 years (34.1%), followed by 65-74 years (29.8%), ≥ 75 years (19.5%), 20-49 years (16.3%), and ≤ 19 years (0.29%). Body habitus in decreasing occurrence was obese (38.6%), overweight (31.9%), healthy weight (27.5%), and underweight (2.1%). Classification by dose indicated 172 patients (≥ 500 mSv) and 3 (≥ 1000 mSv). In comparison, 5.3% of 189,030 CT patients, 1.6% of 18,963 FGI patients, and 0.19% of 41,401 nuclear-medicine patients received CED ≥ 100 mSv from a single modality. CONCLUSIONS: The study of total dose from CT, FGI, and nuclear medicine of patients with CED ≥ 100 mSv indicates major (89%) contribution of CT to CED with 70% of cohort being obese and overweight, and 64% of cohort aged 50-74 years. CLINICAL RELEVANCE STATEMENT: Multimodality recurrent exams are common and there is a lack of information on patient cumulative radiation exposure. This study attempts to address this lacuna and has the potential to motivate actions to improve the justification process for enhancing patient safety. KEY POINTS: • In total, 5.7% of patients undergoing multimodality recurrent imaging (CT, fluoroscopically guided intervention, nuclear medicine) incurred a dose of ≥ 100 mSv. • Mean dose was 184 mSv, with 15 to 18 times contribution from CT than that from fluoroscopically guided intervention or nuclear medicine. • In total, 70% of those who received ≥ 100mSv were either overweight or obese.

CT image quality evaluation in the age of deep learning: trade-off between functionality and fidelity.

OBJECTIVE: To quantitatively compare DLIR and ASiR-V with realistic anatomical images. METHODS: CT scans of an anthropomorphic phantom were acquired using three routine protocols (brain, chest, and abdomen) at four dose levels, with images reconstructed at five levels of ASiR-V and three levels of DLIR. Noise power spectrum (NPS) was estimated using a difference image by subtracting two matching images from repeated scans. Using the max-dose FBP reconstruction as the ground truth, the structure similarity index (SSIM) and gradient magnitude (GM) of difference images were evaluated. Image noise magnitude (σ), frequency location of the NPS peak (fpeak), mean SSIM (MSSIM), and mean GM (MGM) were used as quantitative metrics to compare image quality, for each anatomical region, protocol, algorithm, dose level, and slice thickness. RESULTS: Image noise had a strong (R2 > 0.99) power law relationship with dose for all algorithms. For the abdomen and chest, fpeak shifted from 0.3 (FBP) down to 0.15 mm-1 (ASiR-V 100%) with increasing ASiR-V strength but remained 0.3 mm-1 for all DLIR levels. fpeak shifted down for the brain protocol with increasing DLIR levels. Three levels of DLIR produced similar image noise levels as ASiR-V 40%, 80%, and 100%, respectively. DLIR had lower MSSIM but higher MGM than ASiR-V while matching imaging noise. CONCLUSION: Compared to ASiR-V, DLIR presents trade-offs between functionality and fidelity: it has a noise texture closer to FBP and more edge enhancement, but reduced structure similarity. These trade-offs and unique protocol-dependent behaviors of DLIR should be considered during clinical implementation and deployment. KEY POINTS: • DLIR reconstructed images demonstrate closer noise texture and lower structure similarity to FBP while producing equivalent noise levels comparable to ASiR-V. • DLIR has additional edge enhancement as compared to ASiR-V. • DLIR has unique protocol-dependent behaviors that should be considered for clinical implementation.

Patient-level dose monitoring in computed tomography: tracking cumulative dose from multiple multi-sequence exams with tube current modulation in children.

BACKGROUND: In children exposed to multiple computed tomography (CT) exams, performed with varying z-axis coverage and often with tube current modulation, it is inaccurate to add volume CT dose index (CTDIvol) and size-specific dose estimate (SSDE) to obtain cumulative dose values. OBJECTIVE: To introduce the patient-size-specific z-axis dose profile and its dose line integral (DLI) as new dose metrics, and to use them to compare cumulative dose calculations against conventional measures. MATERIALS AND METHODS: In all children with 2 or more abdominal-pelvic CT scans performed from 2013 through 2019, we retrospectively recorded all series kV, z-axis tube current profile, CTDIvol, dose-length product (DLP) and calculated SSDE. We constructed dose profiles as a function of z-axis location for each series. One author identified the z-axis location of the superior mesenteric artery origin on each series obtained to align the dose profiles for construction of each patient's cumulative profile. We performed pair-wise comparisons between the peak dose of the cumulative patient dose profile and ΣSSDE, and between ΣDLI and ΣDLP. RESULTS: We recorded dose data in 143 series obtained in 48 children, ages 0-2 years (n=15) and 8-16 years (n=33): ΣSSDE 12.7±6.7 and peak dose 15.1±8.1 mGy, ΣDLP 278±194 and ΣDLI 550±292 mGy·cm. Peak dose exceeded ΣSSDE by 20.6% (interquartile range [IQR]: 9.9-26.4%, P<0.001), and ΣDLI exceeded ΣDLP by 114% (IQR: 86.5-147.0%, P<0.001). CONCLUSION: Our methodology represents a novel approach for evaluating radiation exposure in recurring pediatric abdominal CT examinations, both at the individual and population levels. Under a wide range of patient variables and acquisition conditions, graphic depiction of the cumulative z-axis dose profile across and beyond scan ranges, including the peak dose of the profile, provides a better tool for cumulative dose documentation than simple summations of SSDE. ΣDLI is advantageous in characterizing overall energy absorption over ΣDLP, which significantly underestimated this in all children.

Patients undergoing recurrent CT scans: assessing the magnitude.

OBJECTIVES: To assess percent of patients undergoing multiple CT exams that leads to cumulative effective dose (CED) of ≥ 100 mSv and determine their age distribution. METHODS: Data was retrieved retrospectively from established radiation dose monitoring systems by setting the threshold value of 100 mSv at four institutions covering 324 hospitals. The number of patients with CED ≥ 100 mSv only from recurrent CT exams during a feasible time period between 1 and 5 years was identified. Age and gender distribution of these patients were assessed to identify the magnitude of patients in the relatively lower age group of ≤ 50 years. RESULTS: Of the 2.5 million (2,504,585) patients who underwent 4.8 million (4,819,661) CT exams during the period of between 1 and 5 years, a total of 33,407 (1.33%) patients received a CED of ≥ 100 mSv with an overall median CED of 130.3 mSv and maximum of 1185 mSv. Although the vast majority (72-86%) of patients are > 50 years of age, nearly 20% (13.4 to 28%) are ≤ 50 years. The minimum time to accrue 100 mSv was a single day at all four institutions, an unreported finding to date. CONCLUSIONS: We are in an unprecedented era, where patients undergoing multiple CT exams and receiving CED ≥ 100 mSv are not uncommon. While underscoring the need for imaging appropriateness, the consideration of the number and percent of patients with high exposures and related clinical necessities creates an urgent need for the industry to develop CT scanners and protocols with sub-mSv radiation dose, a goal that has been lingering. KEY POINTS: • We are in an era where patients undergoing multiple CT exams during a short span of 1 to 5 years are not uncommon and a sizable fraction among them are below 50 years of age. • This leads to cumulative radiation dose to individual patients at which radiation effects are of real concern. • There is an urgent need for the industry to develop CT scanners with sub-mSv radiation dose, a goal that has been lingering.

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.

Radiation Effective Dose Above 100 mSv From Fluoroscopically Guided Intervention: Frequency and Patient Medical Condition.

OBJECTIVE. The purpose of this article was to investigate the medical condition of patients who received substantial cumulative effective dose (CED) in fluoroscopically guided interventional (FGI) procedures. MATERIALS AND METHODS. We examined 25,253 patients (mean age, 58.2 years; 50.6% male) who underwent 46,491 FGI procedures at a tertiary care center in the United States from January 2010 to January 2019. Radiation dosage data were retrieved from an in-house semiautomated dose-tracking system. A cohort was identified as those who received a CED of 100 mSv or greater and was categorized by medical disorder from longitudinal medical records. Statistical software was used to determine mean value, five percentiles (10th, 25th, 50th, 75th, 95th), and interquartile range for age and dose. RESULTS. Among 1011 (4.0%) patients (30.4% female) with a CED of 100 mSv or more, the median number of procedures was 2.0, the median age at first procedure was 60.0 years old, and the median value of CED was 177.2 mSv. The patients' medical disorders included cancer (36.7%), chronic disease of the torso (30.0%), internal bleeding (24.8%), trauma (4.6%), organ transplant (3.2%) and cerebrovascular disease (0.7%). Eight-hundred (79.1%) patients underwent all of their procedures within 365 days. CONCLUSION. This is the first cohort study of the medical condition of patients receiving substantial cumulative doses from FGI procedures over a long period. In the critical care of patients with serious medical disorders, 4.0% of patients may be exposed to substantial radiation dose (CED ≥ 100 mSv). The risks associated with such a high level of radiation warrant continued attention.

Radiation Dose Monitoring for Fluoroscopically Guided Interventional Procedures: Effect on Patient Radiation Exposure.

Purpose To analyze the clinical effect of continuous dose monitoring and patient follow-up for fluoroscopically guided vascular interventional procedures over 8 years. Materials and Methods In this retrospective study, an in-house semiautomated system was developed for fluoroscopic dose monitoring. The quarterly number of procedures from January 2010 to December 2017 was analyzed with count time series to estimate quarterly change rate. Technologists recorded four dose surrogates in custom fields of institutional dictation software through a Web interface. Radiation doses were transferred automatically to the radiology report and a centralized dose database when the radiologist initiated procedure dictation. A medical physicist reported weekly on procedures with air kerma at the reference point (Ka,r) of 2 Gy or higher to a division-designated radiologist and hospital radiation safety committee who required the attending radiologist to set up follow-up appointments for patients who underwent procedures with a Ka,r greater than or equal to 5 Gy. Results There were a total of 41 585 procedures; 1553 (3.7%) procedures had a Ka,r of 2-5 Gy. Among 240 procedures with Ka,r greater than 5 Gy, 22 had Ka,r greater than 9 Gy. The percentage of high Ka,r procedures decreased over time, going from 5.9% in 2010 to 2.0% in 2017 for procedures with Ka,r of 2-5 Gy and from 1.0% in 2010 to 0.13% in 2017 for procedures with Ka,r greater than or equal to 5 Gy. Relative reduction per quarter was approximately 2.7% (95% confidence interval: 1.5%, 3.8%) for Ka,r of 2-5 Gy and 4.5% (95% confidence interval: 1.5%, 7.6%) for Ka,r greater than or equal to 5 Gy. Conclusion Eight-year temporal trends show three- to eightfold reduction in the number of high-dose procedures. © RSNA, 2019 Online supplemental material is available for this article. See also the editorial by Balter in this issue.

Procedure-specific CT Dose and Utilization Factors for CT-guided Interventional Procedures.

Purpose To present procedure-specific radiation dose metric distributions and define quantitative CT utilization factors for CT-guided interventional procedures. Materials and Methods This single-center, retrospective study collected dictation reports and radiation dose data from 9143 consecutive CT-guided interventional procedures in adult patients from 2012 to 2017. Procedures were sorted into four major interventional categories: ablation, aspiration, biopsy, and drainage, each of which was further divided into subcategories. After exclusion, a total of 8213 procedures (4391 in men and 3822 in women) were divided into 21 subcategories. The mean patient age at examination for men was 62 years ± 15 (standard deviation; age range, 19-114 years), and for women it was 61 years ± 15 (age range, 19-113 years). Distributions of dose metrics and CT usage-related parameters were analyzed by category with descriptive statistic outcomes. Quantitative CT utilization factors (which measure average CT usage) for each interventional subcategory were derived by using total scan length, acquisition count, and number of images. Results Interventional CT scans have distinctly different dose metric characteristics from diagnostic CT scans. Wide variations of dose metrics were observed among subcategories, even within the same major category. For the most frequently performed CT-guided interventional procedures within each major category, liver ablation, chest aspiration, liver biopsy, and single abdominal drainage, the median dose-length product was 2351, 657, 1175, and 1125 mGy ∙ cm, respectively. Procedure-specific CT utilization factors ranged between 0.6 and 3.6. Conclusion This study provides procedure-specific CT dose metric distributions and quantitative CT utilization factors on the basis of a large number of procedures and categorization of CT-guided interventional procedures. © RSNA, 2018.

Quantifying the effect of slice thickness, intravenous contrast and tube current on muscle segmentation: Implications for body composition analysis.

OBJECTIVES: To quantify the effect of IV contrast, tube current and slice thickness on skeletal muscle cross-sectional area (CSA) and density (SMD) on routine CT. METHODS: CSA and SMD were computed on 216 axial CT images obtained at the L3 level in 72 patients with variations in IV contrast, slice thickness and tube current. Intra-patient mean difference (MD), 95 % CI and limits of agreement were calculated using the Bland-Altman approach. Inter- and intra-analyst agreement was evaluated. RESULTS: IV contrast significantly increased CSA by 1.88 % (MD 2.33 cm2; 95 % CI 1.76-2.89) and SMD by 5.99 % (p<0.0001). Five mm slice thickness significantly increased mean CSA by 1.11 % compared to 2 mm images (1.32 cm2; 0.78-1.85) and significantly decreased SMD by 11.64 % (p<0.0001). Low tube current significantly decreased mean CSA by 4.79 % (6.44 cm2; 3.78-9.10) and significantly increased SMD by 46.46 % (p<0.0001). Inter- and intra-analyst agreement was excellent. CONCLUSIONS: IV contrast, slice thickness and tube current significantly affect CSA and SMD. Investigators designing and analysing clinical trials using CT for body composition analysis should report CT acquisition parameters and consider the effect of slice thickness, IV contrast and tube current on myometric data. KEY POINTS: • Intravenous contrast, slice thickness and tube current significantly affect myometric data. • Image acquisition parameter variations may obscure intrapatient muscle differences on serial measurements. • Investigators using CT for body composition analysis should report CT acquisition parameters.

Radiation shielding calculation for digital breast tomosynthesis rooms with an updated workload survey.

PURPOSE: To present shielding calculations for clinical digital breast tomosynthesis (DBT) rooms with updated workload data from a comprehensive survey and to provide reference shielding data for DBT rooms. METHODS: The workload survey was performed from eight clinical DBT (Hologic Selenia Dimensions) rooms at Massachusetts General Hospital (MGH) for the time period between 10/1/2014 and 10/1/2015. Radiation output related information tags from the DICOM header, including mAs, kVp, beam filter material and gantry angle, were extracted from a total of 310 421 clinical DBT acquisitions from the PACS database. DBT workload distributions were determined from the survey data. In combination with previously measured scatter fraction data, unshielded scatter air kerma for each room was calculated. Experiment measurements with a linear-array detector were also performed on representative locations for verification. Necessary shielding material and thickness were determined for all barriers. For the general purpose of DBT room shielding, a set of workload-distribution-specific transmission data and unshielded scatter air kerma values were calculated using the updated workload distribution. RESULTS: The workload distribution for Hologic DBT systems could be simplified by five different kVp/filter combinations for shielding purpose. The survey data showed the predominance of 45° gantry location for medial-lateral-oblique views at MGH. When taking into consideration the non-isotropic scatter fraction distribution together with the gantry angle distribution, accurate and conservative estimate of the unshielded scatter air kerma levels were determined for all eight DBT rooms. Additional shielding was shown to be necessary for two 4.5 cm wood doors. CONCLUSIONS: This study provided a detailed workload survey and updated transmission data and unshielded scatter air kerma values for Hologic DBT rooms. Example shielding calculations were presented for clinical DBT rooms.

Initial Clinical Experience With Extremity Cone-Beam CT of the Foot and Ankle in Pediatric Patients.

OBJECTIVE: Extremity cone-beam CT (CBCT) scanners have become available for clinical use in the United States. The purpose of this study was to review an initial clinical experience with CBCT of the foot and ankle in pediatric patients. MATERIALS AND METHODS: A retrospective review was conducted of all foot or ankle CBCT examinations performed on patients 18 years old and younger at one institution from August 1, 2013, through February 28, 2015. A t test was used to compare mean effective dose for CBCT with that for MDCT foot or ankle examinations of age-matched control subjects. To assess changes in utilization, a t test also was used to compare the mean numbers of foot or ankle CT examinations per month before and after installation of the CBCT scanner at the institution. RESULTS: Thirty-four CBCT examinations were performed. The mean effective dose was 0.013 ± 0.003 mSv compared with 0.023 ± 0.020 mSv for MDCT of age-matched control subjects (p < 0.005). The mean numbers of foot or ankle CT examinations per month were 3.4 in the 18 months before and 3.8 in the 18 months after installation of the CBCT scanner (p = 0.28). The mean number of foot or ankle MDCT examinations per month decreased significantly (3.4 vs 1.9, p = 0.03) over the same period. In 56% of patients, CBCT revealed important findings that were not visible on contemporaneous radiographs. In 68% of patients, the CBCT findings affected clinical management. CONCLUSION: CBCT of the foot or ankle of pediatric patients is a viable lower-dose alternative to MDCT that provides important information that may affect clinical management.

Novel lead-free drape applied to the X-ray detector protects against scatter radiation in the angiography suite.

PURPOSE: To evaluate a sterile, disposable lead-free drape for reducing scatter radiation exposure during fluoroscopy-guided procedures. MATERIALS AND METHODS: Computer-aided design software was used to model a procedure room with a thoracic anthropomorphic phantom on the angiography table. Using this model, measurements of scatter radiation were made from the phantom before and after the application of the drape using a collimated and full field of view in low-output conditions (70 kVp, 48 mA) and high-output conditions (125 kVp, 156 mA). Transmission of x-rays through the drape and entrance exposure rates were also measured. Statistical significance was measured using a Student t test. RESULTS: Scatter radiation was attenuated throughout the procedure room when the drape was applied. The highest level of scatter radiation was detected in the expected position of the operator, adjacent to the phantom. Radioprotection by the drape was the greatest in this position: 71.5% attenuation at waist level and 89% at neck level (P < .0001). The use of the drape did not result in an increase of backscatter radiation to the phantom. CONCLUSIONS: The use of this drape significantly reduces scatter radiation in the procedure room; this effect is maximal in close proximity to the phantom.

Clinical evaluation of a mobile digital specimen radiography system for intraoperative specimen verification.

OBJECTIVE: Use of mobile digital specimen radiography systems expedites intraoperative verification of excised breast specimens. The purpose of this study was to evaluate the performance of a such a system for verifying targets. MATERIALS AND METHODS: A retrospective review included 100 consecutive pairs of breast specimen radiographs. Specimens were imaged in the operating room with a mobile digital specimen radiography system and then with a conventional digital mammography system in the radiology department. Two expert reviewers independently scored each image for image quality on a 3-point scale and confidence in target visualization on a 5-point scale. A target was considered confidently verified only if both reviewers declared the target to be confidently detected. RESULTS: The 100 specimens contained a total of 174 targets, including 85 clips (49%), 53 calcifications (30%), 35 masses (20%), and one architectural distortion (1%). Although a significantly higher percentage of mobile digital specimen radiographs were considered poor quality by at least one reviewer (25%) compared with conventional digital mammograms (1%), 169 targets (97%), were confidently verified with mobile specimen radiography; 172 targets (98%) were verified with conventional digital mammography. Three faint masses were not confidently verified with mobile specimen radiography, and conventional digital mammography was needed for confirmation. One faint mass and one architectural distortion were not confidently verified with either method. CONCLUSION: Mobile digital specimen radiography allows high diagnostic confidence for verification of target excision in breast specimens across target types, despite lower image quality. Substituting this modality for conventional digital mammography can eliminate delays associated with specimen transport, potentially decreasing surgical duration and increasing operating room throughput.

Technical note: Workload and transmission data for mobile C-arm fluoroscopy in gastrointestinal endoscopy.

BACKGROUND: Mobile C-arms may be used in fixed locations, and it is recommended that qualified experts evaluate structural shielding. PURPOSE: To assess clinical workload distributions for mobile C-arms used in gastrointestinal endoscopy and determine the Archer equation parameters for the C-arm beam spectra. METHODS: Consecutive (30 months) gastrointestinal endoscopic procedures on two Cios Alpha systems (Siemens) were retrospectively analyzed. X-ray tube voltage, tube current-time product, reference point air kerma (Ka,r), air kerma-area product (PKA), and fluoroscopic time were examined. The primary beam half-value layer (HVL) was measured with an ionization chamber and aluminum 1100 plates. Stray radiation fraction at 1 m from a scattering source (ACR R/F phantom) was directly measured. Monte Carlo (Geant4) simulation was performed to calculate the transmission of broad X-ray beams through lead, concrete, gypsum, and steel, with X-ray HVLs matching those of the C-arm X-ray beam. The transmission data were fitted to the Archer equation. RESULTS: The number of procedures (3509) was equivalent to 13.48 procedures per room per week. Dose quantities were 54.8 mGy (Ka,r), 18.3 Gy∙cm2 (PKA), and 7.8 min (fluoroscopic time) per procedure. X-ray beam irradiation events were recorded for 2906 (82.8%) procedures with 160,009 events, whose mA-minute weighted tube voltage was 91.0 kV and the workload was 0.68 mA-minute per procedure. The two rooms had a significant difference in the number of procedures per week, 17.3 (29) [mean (maximum)] and 9.6 (16), respectively. The stray radiation fraction was 9.7×10-4 (80 kV) and 1.25×10-3 (120 kV). Transmission fitting parameters were provided for the tube voltage (on average, 90 kV; high end, 120 kV) of the C-arm. CONCLUSIONS: This work provides workload and transmission data for mobile C-arm fluoroscopy in gastrointestinal endoscopy, which indicates a need for structural shielding evaluation of the procedure rooms.

Neurointerventions on two generations of angiography systems: Recent systems reduce radiation exposure by half.

PURPOSE: Fluoroscopically-guided neurointervention may be associated with prolonged procedure time and substantial radiation exposure to the patient and staff. This study sought to examine technological features affecting the potential radiation exposure reduction of new angiography systems, compared to older systems, for neurointerventional procedures. METHODS: Consecutive neurointerventional patients (2020-2022) were retrospectively analyzed. The air kerma at the reference point (Ka,r) and kerma-area product (KAP) were compared between Artis icono and Artis zee (Siemens) using statistical analyses (two-tailed t tests), where P < 0.05 is considered significant. X-ray tube potential and copper filtration were examined. Tests with an anthropomorphic phantom (Sun Nuclear) on Artis icono were conducted and entrance skin exposure and x-ray spectral half value layer were measured. Effective spectral filtration was characterized by x-ray spectral modeling. RESULTS: The number of procedures was 1158 [median (range) age, 59 (7-95) years] on Artis zee and 1087 [60 (1-95) years] on Artis icono, without significant difference in age (p = 0.059) between cohorts. Ka,r was 925.4 (890.6-960.1) mGy [mean (95 % CI)] and KAP was 119.8 (115-124.5) Gy∙cm2 on Artis zee. The measures were 48-50 % lower on Artis icono, 440.5 (411.7-469.4) mGy (Ka,r) and 59.5 (55.4-63.6) Gy∙cm2 (KAP); while the difference in fluoroscopic time between the two generations of angiography systems was insignificant (p = 0.55). CONCLUSIONS: The newer angiography system, with updated hardware and software, was found to result in half the radiation exposure compared to older technology of the same manufacturer, even though fluoroscopic time was similar.

Body CT scanning in young adults: examination indications, patient outcomes, and risk of radiation-induced cancer.

PURPOSE: To quantify patient outcome and predicted cancer risk from body computed tomography (CT) in young adults and identify common indications for the imaging examination. MATERIALS AND METHODS: This retrospective multicenter study was HIPAA compliant and approved by the institutional review boards of three institutions, with waiver of informed consent. The Research Patient Data Registry containing patient medical and billing records of three university-affiliated hospitals in a single metropolitan area was queried for patients 18-35 years old with a social security record who underwent chest or abdominopelvic CT from 2003 to 2007. Patients were analyzed according to body part imaged and scanning frequency. Mortality status and follow-up interval were recorded. The Biologic Effects of Ionizing Radiation VII method was used to calculate expected cancer incidence and death. Examination indication was determined with associated ICD-9 diagnostic code; 95% confidence intervals for percentages were calculated, and the binomial test was used to compare the difference between percentages. RESULTS: In 21 945 patients, 16 851 chest and 24 112 abdominopelvic CT scans were obtained. During the average 5.5-year (± 0.1 [standard deviation]) follow-up, 7.1% (575 of 8057) of chest CT patients and 3.9% (546 of 13 888) of abdominal CT patients had died. In comparison, the predicted risk of dying from CT-induced cancer was 0.1% (five of 8057, P < .01) and 0.1% (eight of 12 472, P < .01), respectively. The most common examination indications were cancer and trauma for chest CT and abdominal pain, trauma, and cancer for abdominopelvic CT. Among patients without a cancer diagnosis in whom only one or two scans were obtained, mortality and predicted risk of radiation-induced cancer death were 3.6% (215 of 5914) and 0.05% (three of 5914, P < .01) for chest CT and 1.9% (219 of 11 291) and 0.1% (six of 11 291, P < .01) for abdominopelvic CT. CONCLUSION: Among young adults undergoing body CT, risk of death from underlying morbidity is more than an order of magnitude greater than death from long-term radiation-induced cancer.

Patients with testicular cancer undergoing CT surveillance demonstrate a pitfall of radiation-induced cancer risk estimates: the timing paradox.

PURPOSE: To demonstrate a limitation of lifetime radiation-induced cancer risk metrics in the setting of testicular cancer surveillance-in particular, their failure to capture the delayed timing of radiation-induced cancers over the course of a patient's lifetime. MATERIALS AND METHODS: Institutional review board approval was obtained for the use of computed tomographic (CT) dosimetry data in this study. Informed consent was waived. This study was HIPAA compliant. A Markov model was developed to project outcomes in patients with testicular cancer who were undergoing CT surveillance in the decade after orchiectomy. To quantify effects of early versus delayed risks, life expectancy losses and lifetime mortality risks due to testicular cancer were compared with life expectancy losses and lifetime mortality risks due to radiation-induced cancers from CT. Projections of life expectancy loss, unlike lifetime risk estimates, account for the timing of risks over the course of a lifetime, which enabled evaluation of the described limitation of lifetime risk estimates. Markov chain Monte Carlo methods were used to estimate the uncertainty of the results. RESULTS: As an example of evidence yielded, 33-year-old men with stage I seminoma who were undergoing CT surveillance were projected to incur a slightly higher lifetime mortality risk from testicular cancer (598 per 100 000; 95% uncertainty interval [UI]: 302, 894) than from radiation-induced cancers (505 per 100 000; 95% UI: 280, 730). However, life expectancy loss attributable to testicular cancer (83 days; 95% UI: 42, 124) was more than three times greater than life expectancy loss attributable to radiation-induced cancers (24 days; 95% UI: 13, 35). Trends were consistent across modeled scenarios. CONCLUSION: Lifetime radiation risk estimates, when used for decision making, may overemphasize radiation-induced cancer risks relative to short-term health risks.

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.

Patient follow-up for possible radiation injury from fluoroscopically-guided interventions: Need to consider high cumulative exposure from multiple procedures.

PURPOSE: Patient skin dose from interventional fluoroscopy procedures may exceed the threshold of tissue injuries and established guidelines recommend patient follow-up for air kerma at reference point (Ka,r) ≥ 5 Gy for individual procedures. Patients may undergo multiple procedures and skin injuries may be possible by cumulative exposure, even when individually insufficient to cause injury. This study sought to quantify the frequency of patients whose individual procedure doses are below 5 Gy but whose cumulative Ka,r is ≥ 5 Gy. METHODS: This retrospective study analyzed 37,917 consecutive procedures in interventional radiology and vascular surgery at a tertiary-care hospital between January 2016 and June 2021. Radiation dosage was retrieved from the fluoroscopy acquisition systems. For a patient receiving multiple procedures, but each with Ka,r < 5 Gy, cumulative Ka,r within 2, 7, 14, 30, 183, and 365 days was assessed. RESULTS: Nearly 1/3rd (37.4 %) patients underwent multiple procedures. With individual procedures of Ka,r < 5 Gy exclusively, 1.9, 4.4, and 5.6 in 1000 patients received cumulative Ka,r of 5-14.1 Gy from the procedures within 30, 183, and 365 days, respectively. From the procedures within 14 days, 1.3 in 1000 patients received cumulative Ka,r of 5-11.4 Gy; and from those within 7 days, 0.87 in 1000 patients received 5-9.1 Gy. In comparison, 4.3 in 1000 patients received Ka,r of 5-12 Gy from a single procedure. CONCLUSIONS: In the absence of guidelines on patient follow-up for multiple procedures, our study may provide good material for setting up such guidelines.

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.