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

OBJECTIVE: To determine patient, institution, and machine characteristics that contribute to variation in radiation doses used for computed tomography (CT). DESIGN: Prospective cohort study. SETTING: Data were assembled and analyzed from the University of California San Francisco CT International Dose Registry. PARTICIPANTS: Standardized data from over 2.0 million CT examinations of adults who underwent CT between November 2015 and August 2017 from 151 institutions, across seven countries (Switzerland, Netherlands, Germany, United Kingdom, United States, Israel, and Japan). MAIN OUTCOME MEASURES: Mean effective doses and proportions of high dose examinations for abdomen, chest, combined chest and abdomen, and head CT were determined by patient characteristics (sex, age, and size), type of institution (trauma center, care provision 24 hours per day and seven days per week, academic, private), institutional practice volume, machine factors (manufacturer, model), country, and how scanners were used, before and after adjustment for patient characteristics, using hierarchical linear and logistic regression. High dose examinations were defined as CT scans with doses above the 75th percentile defined during a baseline period. RESULTS: The mean effective dose and proportion of high dose examinations varied substantially across institutions. The doses varied modestly (10-30%) by type of institution and machine characteristics after adjusting for patient characteristics. By contrast, even after adjusting for patient characteristics, wide variations in radiation doses across countries persisted, with a fourfold range in mean effective dose for abdomen CT examinations (7.0-25.7 mSv) and a 17-fold range in proportion of high dose examinations (4-69%). Similar variation across countries was observed for chest (mean effective dose 1.7-6.4 mSv, proportion of high dose examinations 1-26%) and combined chest and abdomen CT (10.0-37.9 mSv, 2-78%). Doses for head CT varied less (1.4-1.9 mSv, 8-27%). In multivariable models, the dose variation across countries was primarily attributable to institutional decisions regarding technical parameters (that is, how the scanners were used). CONCLUSIONS: CT protocols and radiation doses vary greatly across countries and are primarily attributable to local choices regarding technical parameters, rather than patient, institution, or machine characteristics. These findings suggest that the optimization of doses to a consistent standard should be possible. STUDY REGISTRATION: Clinicaltrials.gov NCT03000751.

The benefits of using a bismuth-containing, radiation-absorbing drape in cardiac resynchronization implant procedures.

BACKGROUND: Radiation exposure is a major concern in cardiac device implantation, especially cardiac resynchronization therapy (CRT) procedures. The RadPad™ (Worldwide Innovations & Technologies, Inc., Kansas City, MO, USA), a radiation-attenuating adhesive drape, has been shown to be beneficial in several clinical settings involving fluoroscopy, but less is known about the actual benefits in CRT procedures. METHODS: Consecutive CRT implants performed with and without a RadPad™ drape over a 10-month period were analyzed. Two thermoluminescent dosimeters (TLDs) were attached to each implanting physician at several locations (adjacent to eyes, center abdomen [outside lead apron], left and right index fingers, and dorsum of the right foot). Results were corrected for background using control TLDs, and normalized to dose-area product (DAP). RESULTS: Thirty-six patients (31 male), 16 with and 20 without the RadPad™, were included in the study. No technical problems were caused by the presence of the radiation-absorbing drape. Time required to position the drape never exceeded 30 seconds, no acute skin reactions were noted, and no radiation-absorbing drape became displaced. Despite a trend toward longer fluoroscopy times and higher DAPs in the radiation-absorbing drape group, radiation exposure was significantly reduced: 65% in the case of the hands and body (P < 0.001), and 40% the eyes (P < 0.01). CONCLUSION: The use of a radiation-absorbing drape results in a significant reduction in radiation dose to the implanting physician during CRT procedures. Not only is the dose to the hands reduced, but also the eye and body doses are significantly reduced. The routine use of radiation-absorbing drapes should be considered for all CRT implant procedures in the light of these findings.

Quantification and normalization of x-ray mammograms.

The analysis of (x-ray) mammograms remains qualitative, relying on the judgement of clinicians. We present a novel method to compute a quantitative, normalized measure of tissue radiodensity traversed by the primary beam incident on each pixel of a mammogram, a measure we term the standard attenuation rate (SAR). SAR enables: the estimation of breast density which is linked to cancer risk; direct comparison between images; the full potential of computer aided diagnosis to be utilized; and a basis for digital breast tomosynthesis reconstruction. It does this by removing the effects of the imaging conditions under which the mammogram is acquired. First, the x-ray spectrum incident upon the breast is calculated, and from this, the energy exiting the breast is calculated. The contribution of scattered radiation is calculated and subtracted. The SAR measure is the scaling factor that must be applied to the reference material in order to match the primary attenuation of the breast. Specifically, this is the scaled reference material attenuation which when traversed by an identical beam to that traversing the breast, and when subsequently detected, results in the primary component of the pixel intensity observed in the breast image. We present results using two tissue equivalent phantoms, as well as a sensitivity analysis to detector response changes over time and possible errors in compressed thickness measurement.

A model of primary and scattered photon fluence for mammographic x-ray image quantification.

We present an efficient method to calculate the primary and scattered x-ray photon fluence component of a mammographic image. This can be used for a range of clinically important purposes, including estimation of breast density, personalized image display, and quantitative mammogram analysis. The method is based on models of: the x-ray tube; the digital detector; and a novel ray tracer which models the diverging beam emanating from the focal spot. The tube model includes consideration of the anode heel effect, and empirical corrections for wear and manufacturing tolerances. The detector model is empirical, being based on a family of transfer functions that cover the range of beam qualities and compressed breast thicknesses which are encountered clinically. The scatter estimation utilizes optimal information sampling and interpolation (to yield a clinical usable computation time) of scatter calculated using fundamental physics relations. A scatter kernel arising around each primary ray is calculated, and these are summed by superposition to form the scatter image. Beam quality, spatial position in the field (in particular that arising at the air-boundary due to the depletion of scatter contribution from the surroundings), and the possible presence of a grid, are considered, as is tissue composition using an iterative refinement procedure. We present numerous validation results that use a purpose designed tissue equivalent step wedge phantom. The average differences between actual acquisitions and modelled pixel intensities observed across the adipose to fibroglandular attenuation range vary between 5% and 7%, depending on beam quality and, for a single beam quality are 2.09% and 3.36% respectively with and without a grid.