Radiation Doses in Interventional Radiology Procedures: The RAD-IR Study: Part III: Dosimetric Performance of the Interventional Fluoroscopy Units

doi:10.1097/01.RVI.0000130864.68139.08

Journal of Vascular and Interventional Radiology

Volume 15, Issue 9, September 2004, Pages 919-926

https://doi.org/10.1097/01.RVI.0000130864.68139.08 Get rights and content

PURPOSE

To present the physics data supporting the validity of the clinical dose data from the RAD-IR study and to document the performance of dosimetry-components of these systems over time.

MATERIALS AND METHODS

Sites at seven academic medical centers in the United States prospectively contributed data for each of 12 fluoroscopic units. All units were compatible with International Electrotechnical Commission (IEC) standard 60601-2-43. Comprehensive evaluations and periodic consistency checks were performed to verify the performance of each unit's dosimeter. Comprehensive evaluations compared system performance against calibrated ionization chambers under nine combinations of operating conditions. Consistency checks provided more frequent dosimetry data, with use of each unit's built-in dosimetry equipment and a standard water phantom.

RESULTS

During the 3-year study, data were collected for 48 comprehensive evaluations and 581 consistency checks. For the comprehensive evaluations, the mean (95% confidence interval range) ratio of system to external measurements was 1.03 (1.00–1.05) for fluoroscopy and 0.93 (0.90–0.96) for acquisition. The expected ratio was 0.93 for both. For consistency checks, the values were 1.00 (0.98–1.02) for fluoroscopy and 1.00 (0.98–1.02) for acquisition. Each system was compared across time to its own mean value. Overall uncertainty was estimated by adding the standard deviations of the comprehensive and consistency measurements in quadrature. The authors estimate that the overall error in clinical cumulative dose measurements reported in RAD-IR is 24%.

CONCLUSION

Dosimetric accuracy was well within the tolerances established by IEC standard 60601-2-43. The clinical dose data reported in the RAD-IR study are valid.

Section snippets

Radiation Dose Quantities

The unmodified word “dose” is used with only one of its many meanings in this report and others of the RAD-IR series (a glossary of radiobiological terms is included in Parts I and II of the RAD-IR study) (2, 3). In this report, dose means air-kerma without scatter. This meaning is consistent with the usage found in relevant Federal Drug Administration (FDA) and IEC documentation (4, 5, 6).

Skin dose can be calculated from air-kerma at the skin with use of wellknown techniques and measurements

Comprehensive Physics

Forty-eight sets of comprehensive physics measurements were collected during the course of the study, with two to five data sets collected on each individual imaging plane. All sites completed initial and final evaluations for each plane. As anticipated, some imaging planes required additional measurements after x-ray tube replacement.

The reference ionization chambers used at each site were required to have a current compliance or calibration certificate, were presumed to be accurate and were

DISCUSSION

Sources of error in cumulative dose measurements include DAP sensor output, conversion of DAP to cumulative dose and reference ionization chamber accuracy. Variations in the output of the DAP sensor result from variations in beam energy and filtration, DAP rate, irradiation time, field size, operating voltage, local air pressure, temperature, humidity, and electromagnetic compatibility. The range of phantom material thickness and exposure modes used for comprehensive physics measurements

Acknowledgment

The authors thank Hannes Seissl (Siemens AG Medical Solutions, Forchheim, Germany), for his technical descriptions, manufacturer's calibration procedural information, and other related inputs into this project and report.

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Radiation doses in interventional radiology: the RAD-IR study part I. Overall measures of dose
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Patient Radiation Doses in IR Procedures: The American College of Radiology Dose Index Registry-Fluoroscopy Pilot
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To update normative data on fluoroscopy dose indices in the United States for the first time since the Radiation Doses in Interventional Radiology study in the late 1990s.
The Dose Index Registry-Fluoroscopy pilot study collected data from March 2018 through December 2019, with 50 fluoroscopes from 10 sites submitting data. Primary radiation dose indices including fluoroscopy time (FT), cumulative air kerma (K_a,r), and kerma area product (P_KA) were collected for interventional radiology fluoroscopically guided interventional (FGI) procedures. Clinical facility procedure names were mapped to the American College of Radiology (ACR) common procedure lexicon. Distribution parameters including the 10th, 25th, 50th, 75th, 95th, and 99th percentiles were computed.
Dose indices were collected for 70,377 FGI procedures, with 50,501 ultimately eligible for analysis. Distribution parameters are reported for 100 ACR Common IDs. FT in minutes, K_a,r in mGy, and P_KA in Gy-cm² are reported in this study as (n; median) for select ACR Common IDs: inferior vena cava filter insertion (1,726; FT: 2.9; K_a,r: 55.8; P_KA: 14.19); inferior vena cava filter removal (464; FT: 5.7; K_a,r: 178.6; P_KA: 34.73); nephrostomy placement (2,037; FT: 4.1; K_a,r: 39.2; P_KA: 6.61); percutaneous biliary drainage (952; FT: 12.4; K_a,r: 160.5; P_KA: 21.32); gastrostomy placement (1,643; FT: 3.2; K_a,r: 29.1; P_KA: 7.29); and transjugular intrahepatic portosystemic shunt placement (327; FT: 34.8; K_a,r: 813.0; P_KA: 181.47).
The ACR DIR-Fluoro pilot has provided state-of-the-practice statistics for radiation dose indices from IR FGI procedures. These data can be used to prioritize procedures for radiation optimization, as demonstrated in this work.
Patient Radiation Doses in Interventional Radiology Procedures: Comparison of Fluoroscopy Dose Indices between the American College of Radiology Dose Index Registry-Fluoroscopy Pilot and the Radiation Doses in Interventional Radiology Study
2023, Journal of Vascular and Interventional Radiology
To compare radiation dose index distributions for fluoroscopically guided interventions in interventional radiology from the American College of Radiology (ACR) Fluoroscopy Dose Index Registry (DIR-Fluoro) pilot to those from the Radiation Doses in Interventional Radiology (RAD-IR) study.
Individual and grouped ACR Common identification numbers (procedure types) from the DIR-Fluoro pilot were matched to procedure types in the RAD-IR study. Fifteen comparisons were made. Distribution parameters, including the 10th, 25th, 50th, 75th, and 95th percentiles, were compared for fluoroscopy time (FT), cumulative air kerma (K_a,r), and kerma area product (P_KA). Two derived indices were computed using median dose indices. The procedure-averaged reference air kerma rate ( $\bar{K_{a, r}}$ ) was computed as K_a,r / FT. The procedure-averaged x-ray field size at the reference point (A_r) was computed as P_KA / (K_a,r × 1,000).
The median FT was equally likely to be higher or lower in the DIR-Fluoro pilot as it was in the RAD-IR study, whereas the maximum FT was almost twice as likely to be higher in the DIR-Fluoro pilot than it was in the RAD-IR study. The median K_a,r was lower in the DIR-Fluoro pilot for all procedures, as was median P_KA. The maximum K_a,r and P_KA were more often higher in the DIR-Fluoro pilot than in the RAD-IR study. $\bar{K_{a, r}}$ followed the same pattern as K_a,r, whereas A_r was often greater in DIR-Fluoro.
The median dose indices have decreased since the RAD-IR study. The typical K_a,r rates are lower, a result of the use of lower default dose rates. However, opportunities for quality improvement exist, including renewed focus on tight collimation of the imaging field of view.
Monte Carlo simulations and phantom validation of low-dose radiotherapy to the lungs using an interventional radiology C-arm fluoroscope
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To use MC simulations and phantom measurements to investigate the dosimetry of a kilovoltage x-ray beam from an IR fluoroscope to deliver low-dose (0.3–1.0 Gy) radiotherapy to the lungs.
PENELOPE was used to model a 125 kV, 5.94 mm Al HVL x-ray beam produced by a fluoroscope. The model was validated through depth-dose, in-plane/cross-plane profiles and absorbed dose at 2.5-, 5.1-, 10.2- and 15.2-cm depths against the measured beam in an acrylic phantom. CT images of an anthropomorphic phantom thorax/lungs were used to simulate 0.5 Gy dose distributions for PA, AP/PA, 3-field and 4-field treatments. DVHs were generated to assess the dose to the lungs and nearby organs. Gafchromic film was used to measure doses in the phantom exposed to PA and 4-field treatments, and compared to the MC simulations.
Depth-dose and profile results were within 3.2% and 7.8% of the MC data uncertainty, respectively, while dose gamma analysis ranged from 0.7 to 1.0. Mean dose to the lungs were 1.1-, 0.8-, 0.9-, and 0.8- Gy for the PA, AP/PA, 3-field, and 4-field after isodose normalization to cover ∼ 95% of each lung volume. Skin dose toxicity was highest for the PA and lowest for the 4-field, and both arrangements successfully delivered the treatment on the phantom. However, the dose distribution for the PA was highly non-uniform and produced skin doses up to 4 Gy. The dose distribution for the 4-field produced a uniform 0.6 Gy dose throughout the lungs, with a maximum dose of 0.73 Gy. The average percent difference between experimental and Monte Carlo values were −0.1% (range −3% to +4%) for the PA treatment and 0.3% (range −10.3% to +15.2%) for the 4-field treatment.
A 125 kV x-ray beam from an IR fluoroscope delivered through two or more fields can deliver an effective low-dose radiotherapy treatment to the lungs. The 4-field arrangement not only provides an effective treatment, but also significant dose sparing to healthy organs, including skin, compared to the PA treatment. Use of fluoroscopy appears to be a viable alternative to megavoltage radiation therapy equipment for delivering low-dose radiotherapy to the lungs.
The American College of Radiology Fluoroscopy Dose Index Registry Pilot: Technical Considerations and Dosimetric Performance of the Interventional Fluoroscopes
2020, Journal of Vascular and Interventional Radiology
Citation Excerpt :
Radiation dose indices were also stable over the course of the pilot for the 28 imaging planes with evaluations available from the 3 time points. These results are similar to those reported previously, including those reported in the RAD-IR study (3,7). The RAD-IR study (3) reported the ratio of the displayed index to the measured index, which is the reciprocal of the correction factors reported in the present study.
To characterize the accuracy and consistency of fluoroscope dose index reporting and report rates of occupational radiation safety hardware availability and use, trainee participation in procedures, and optional hardware availability at pilot sites for the American College of Radiology (ACR) Fluoroscopy Dose Index Registry (DIR).
Nine institutions participated in the registry pilot, providing fluoroscopic technical and clinical practice data from 38 angiographic C-arm–type fluoroscopes. These data included measurements of the procedure table and mattress transmission factors and accuracy measurements of the reference-point air kerma (K_a,r) and air kerma–area product (P_KA). The accuracy of the radiation dose indices were analyzed for variation over time by 1-way analysis of variance (ANOVA). Sites also self-reported information on availability and use of radiation safety hardware, hardware configuration of fluoroscopes, and trainee participation in procedures.
All K_a,r and P_KA measurements were within the ±35% regulatory limit on accuracy. The mean absolute difference between correction factors for a given system in fluoroscopic and acquisition mode was 0.03 (95% confidence interval, 0.03–0.03). For the 28 fluoroscopic imaging planes that provided data for 3 time points, ANOVA yielded an F value of 0.134 with an F-critical value of 3.109 (P = .875).
This publication provides the technical and clinical framework pertaining to the ACR Fluoroscopy DIR pilot and offers necessary context for future analysis of the clinical procedure radiation-dose data collected.
Impact of low dose settings on radiation exposure during pediatric fluoroscopic guided interventions
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A comprehensive report investigating the use of interventional procedures in 20 countries, including developing countries, has emphasized the need to promote radiation safety precautions especially for pediatric patients [1]. While robust data about fluoroscopy dose metrics has been collected in adults [2–4], most of the knowledge regarding pediatric fluoroscopy dose metrics during interventional procedures is obtained from cardiac catheterization procedures as well as neuroradiological interventions [5,6]. Only recently, comprehensive data on pediatric radiation doses have been reported and reference levels for pediatric interventional procedures have been suggested [7].
To evaluate the effects of lowering the detector entrance exposure in children undergoing interventional radiology procedures.
The study retrospectively investigated radiation dose levels in pediatric patients aged 0–18 years before (n = 39) and after (n = 26) lowering detector entrance dose, undergoing embolization of peripheral Arteriovenous malformations, Portal Vein Interventions or Percutaneous Transhepatic Cholangio Drainage (PTCD) between 2014 and 2017. Patient characteristics, fluoroscopy time, protocols used as well as resulting Skin Dose and Dose Area Product (DAP) were compared in each cohort. Image quality was assessed by two independent readers.
The two patient cohorts did not differ in terms of patient demographics. Similarly, fluoroscopy time did not differ before and after implementation of the low dose settings. An overall reduction of skin dose of 75.1% for AVM embolizations, 80.5% for Portal Vein Interventions and 85.3% for PTCD placement was observed. The DAP decrease was 82.5% for AVM embolizations, 72.2% for Portal Vein Interventions and 79.8% for PTCD placement. Image quality was generally considered to be good with an insignificant difference between pre and post implementation of the low dose approach and good agreement between the two readers. Manual inroom-switching to higher dose levels was possible, however this was not performed more frequently after implementation of the low dose settings.
Lowering the detector entrance dose in pediatric interventional radiology procedures results in a significant decrease of the radiation dose burden.
Understanding and Using Fluoroscopic Dose Display Information
2015, Current Problems in Diagnostic Radiology
Fluoroscopically guided procedures are an area of radiology in which radiation exposure to the patient is highly operator dependent. Modern fluoroscopy machines display a variety of information, including technique factors, field of view, operating geometry, exposure mode, fluoroscopic time, air kerma at the reference point (RAK), and air kerma area-product. However, the presentation of this information is highly vendor specific, and many users are unaware of how to interpret this information and use it to perform a study with the minimum necessary dose. A conceptual framework for understanding the radiation dose readout during a procedure is to compare it to the dashboard of an automobile, where the rate at which radiation is being applied (the RAK rate [mGy/min]) is the dose “speed” and the cumulative amount of radiation applied (cumulative RAK [mGy]) is the dose “odometer.” This analogy can be used as a starting point to improve knowledge of these parameters, including how RAK is measured, how RAK correlates with skin dose, and how parameters are displayed differently during fluoroscopy and fluorography. Awareness of these factors is critical to understanding how dose parameters translate to patient risk and the consequences of high-dose studies. With this increased awareness, physicians performing fluoroscopically guided procedures can understand how to use built-in features of the fluoroscopic equipment (pulse rate, beam filtration, and automatic exposure control) and fluoroscopic techniques (procedure planning, patient positioning, proper collimation, and magnification) to reduce patient radiation dose, thereby improving patient safety.

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Supported in part by a grant from the Cardiovascular and Interventional Radiology Research and Education Foundation.

None of the authors have identified a potential conflict of interest.

The opinions expressed herein are those of the authors and do not necessarily reflect those of the United States Navy, the Department of Defense, or the Department of Health and Human Services

¹: Current affiliation: Department of Radiology, Lahey Clinic, Burlington, Massachusetts.

²: Current affiliation: Division of Neuroendovascular Surgery, University of Illinois at Chicago, Chicago, Illinois.

³: Current affiliation: Department of Radiology, University of Colorado Health Sciences Center, Denver, Colorado.

⁴: Current affiliation: Department of Radiology, Hahnemann University Hospital, Drexel College of Medicine, Philadelphia, Pennsylvania.

⁵: Current affiliation: Trinity Imaging and Intervention, Trinity Clinic, Tyler, Texas.

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