Randell Kruger

Use of diagnostic imaging studies and associated radiation exposure for patients enrolled in large integrated health care systems, 1996-2010

CONTEXT Use of diagnostic imaging has increased significantly within fee-for-service models of care. Little is known about patterns of imaging among members of integrated health care systems. OBJECTIVE To estimate trends in imaging utilization and associated radiation exposure among members of integrated health care systems. DESIGN, SETTING, AND PARTICIPANTS Retrospective analysis of electronic records of members of 6 large integrated health systems from different regions of the United States. Review of medical records allowed direct estimation of radiation exposure from selected tests. Between 1 million and 2 million member-patients were included each year from 1996 to 2010. MAIN OUTCOME MEASURE Advanced diagnostic imaging rates and cumulative annual radiation exposure from medical imaging. RESULTS During the 15-year study period, enrollees underwent a total of 30.9 million imaging examinations (25.8 million person-years), reflecting 1.18 tests (95% CI, 1.17-1.19) per person per year, of which 35% were for advanced diagnostic imaging (computed tomography [CT], magnetic resonance imaging [MRI], nuclear medicine, and ultrasound). Use of advanced diagnostic imaging increased from 1996 to 2010; CT examinations increased from 52 per 1000 enrollees in 1996 to 149 per 1000 in 2010, 7.8% annual increase (95% CI, 5.8%-9.8%); MRI use increased from 17 to 65 per 1000 enrollees, 10% annual growth (95% CI, 3.3%-16.5%); and ultrasound rates increased from 134 to 230 per 1000 enrollees, 3.9% annual growth (95% CI, 3.0%-4.9%). Although nuclear medicine use decreased from 32 to 21 per 1000 enrollees, 3% annual decline (95% CI, 7.7% decline to 1.3% increase), PET imaging rates increased after 2004 from 0.24 to 3.6 per 1000 enrollees, 57% annual growth. Although imaging use increased within all health systems, the adoption of different modalities for anatomic area assessment varied. Increased use of CT between 1996 and 2010 resulted in increased radiation exposure for enrollees, with a doubling in the mean per capita effective dose (1.2 mSv vs 2.3 mSv) and the proportion of enrollees who received high (>20-50 mSv) exposure (1.2% vs 2.5%) and very high (>50 mSv) annual radiation exposure (0.6% vs 1.4%). By 2010, 6.8% of enrollees who underwent imaging received high annual radiation exposure (>20-50 mSv) and 3.9% received very high annual exposure (>50 mSv). CONCLUSION Within integrated health care systems, there was a large increase in the rate of advanced diagnostic imaging and associated radiation exposure between 1996 and 2010.

Normalized CT dose index of the CT scanners used in the National Lung Screening Trial

OBJECTIVE The National Lung Screening Trial includes 33 participating institutions that performed 75,133 lung cancer screening CT examinations for 26,724 subjects during 2002-2007. For trial quality assurance reasons, CT radiation dose measurement data were collected from all MDCT scanners used in the trial. MATERIALS AND METHODS A total of 247 measurements on 96 MDCT scanners were collected using a standard CT dose index (CTDI) measurement protocol. The scan parameters used in the measurements (tube voltage, milliampere-seconds [mAs], and detector-channel configuration) were set according to trial protocol for average size subjects. The normalized weighted CT dose index (CTDI(w)) (computed as CTDI(w)/mAs) obtained from each trial-participating scanner was tabulated. RESULTS We found a statistically significant difference in normalized CT dose index among CT scanner manufacturers, likely as a result of design differences, such as filtration, bow-tie design, and geometry. Our findings also indicated a statistically significant difference in normalized CT dose index among CT scanner models from the same manufacturer (e.g., GE Healthcare, Siemens Healthcare, and Philips Healthcare). We also found a statistically significant difference in normalized CT dose index among all models and all manufacturers; furthermore, we found a statistically significant difference in normalized CT dose index among CT scanners from all manufacturers when we compared scanners with four or eight data channels to those with 16, 32, or 64 channels, suggesting that more complex scanners have improved dose efficiency. CONCLUSION Average normalized CT dose index values varied by a factor of almost two for all scanners from all manufacturers. This study was focused on machine-specific normalized CT dose index; patient dose and image quality were not addressed.

Calculation of Organ Doses for a Large Number of Patients Undergoing CT Examinations

OBJECTIVE The objective of our study was to develop an automated calculation method to provide organ dose assessment for a large cohort of pediatric and adult patients undergoing CT examinations. MATERIALS AND METHODS We adopted two dose libraries that were previously published: the volume CT dose index-normalized organ dose library and the tube current-exposure time product (100 mAs)-normalized weighted CT dose index library. We developed an algorithm to calculate organ doses using the two dose libraries and the CT parameters available from DICOM data. We calculated organ doses for pediatric (n = 2499) and adult (n = 2043) CT examinations randomly selected from four health care systems in the United States and compared the adult organ doses with the values calculated from the ImPACT calculator. RESULTS The median brain dose was 20 mGy (pediatric) and 24 mGy (adult), and the brain dose was greater than 40 mGy for 11% (pediatric) and 18% (adult) of the head CT studies. Both the National Cancer Institute (NCI) and ImPACT methods provided similar organ doses (median discrepancy < 20%) for all organs except the organs located close to the scanning boundaries. The visual comparisons of scanning coverage and phantom anatomies revealed that the NCI method, which is based on realistic computational phantoms, provides more accurate organ doses than the ImPACT method. CONCLUSION The automated organ dose calculation method developed in this study reduces the time needed to calculate doses for a large number of patients. We have successfully used this method for a variety of CT-related studies including retrospective epidemiologic studies and CT dose trend analysis studies.

Body Size–Specific Organ and Effective Doses of Chest CT Screening Examinations of the National Lung Screening Trial

OBJECTIVE We calculated body size-specific organ and effective doses for 23,734 participants in the National Lung Screening Trial (NLST) using a CT dose calculator. MATERIALS AND METHODS We collected participant-specific technical parameters of 23,734 participants who underwent CT in the clinical trial. For each participant, we calculated two sets of organ doses using two methods. First, we computed body size-specific organ and effective doses using the National Cancer Institute CT (NCICT) dosimetry program, which is based on dose coefficients derived from a library of body size-dependent adult male and female computational phantoms. We then recalculated organ and effective doses using dose coefficients from reference size phantoms for all examinations to investigate potential errors caused by the lack of body size consideration in the dose calculations. RESULTS The underweight participants (body mass index [BMI; weight in kilograms divided by the square of height in meters] < 18.5) received 1.3-fold greater lung dose (median, 4.93 mGy) than the obese participants (BMI > 30) (3.90 mGy). Thyroid doses were approximately 1.3- to 1.6-fold greater than the lung doses (6.3-6.5 mGy). The reference phantom-based dose calculation underestimates the body size-specific lung dose by up to 50% for the underweight participants and overestimates that value by up to 200% for the overweight participants. The median effective dose ranges from 2.01 mSv in obese participants to 2.80 mSv in underweight participants. CONCLUSION Body size-specific organ and effective doses were computed for 23,734 NLST participants who underwent low-dose CT screening. The use of reference size phantoms can lead to significant errors in organ dose estimates when body size is not considered in the dose assessment.

WE‐B‐207‐01: CT Lung Cancer Screening and the Medical Physicist: Background, Findings and Participant Dosimetry Summary of the National Lung Screening Trial (NLST)

The US National Lung Screening Trial (NLST) was a multi-center randomized, controlled trial comparing a low-dose CT (LDCT) to posterior-anterior (PA) chest x-ray (CXR) in screening older, current and former heavy smokers for early detection of lung cancer. Recruitment was launched in September 2002 and ended in April 2004 when 53,454 participants had been randomized at 33 screening sites in equal proportions. Funded by the National Cancer Institute this trial demonstrated that LDCT screening reduced lung cancer mortality. The US Preventive Services Task Force (USPSTF) cited NLST findings and conclusions in its deliberations and analysis of lung cancer screening. Under the 2010 Patient Protection and Affordable Care Act, the USPSTF favorable recommendation regarding lung cancer CT screening assisted in obtaining third-party payers coverage for screening. The objective of this session is to provide an introduction to the NLST and the trial findings, in addition to a comprehensive review of the dosimetry investigations and assessments completed using individual NLST participant CT and CXR examinations. Session presentations will review and discuss the findings of two independent assessments, a CXR assessment and the findings of a CT investigation calculating individual organ dosimetry values. The CXR assessment reviewed a total of 73,733 chest x-ray exams that were performed on 92 chest imaging systems of which 66,157 participant examinations were used. The CT organ dosimetry investigation collected scan parameters from 23,773 CT examinations; a subset of the 75,133 CT examinations performed using 97 multi-detector CT scanners. Organ dose conversion coefficients were calculated using a Monte Carlo code. An experimentally-validated CT scanner simulation was coupled with 193 adult hybrid computational phantoms representing the height and weight of the current U.S. population. The dose to selected organs was calculated using the organ dose library and the abstracted scan parameters. This session will review the results and summarize the individualized doses to major organs and the mean effective dose and CTDIvol estimate for 66,157 PA chest and 23,773 CT examinations respectively, using size-dependent computational phantoms coupled with Monte Carlo calculations. Learning Objectives: 1.Review and summarize relevant NLST findings and conclusions. 2.Understand the scope and scale of the NLST specific to participant dosimetry. 3.Provide a comprehensive review of NLST participant dosimetry assessments. 4.Summarize the results of an investigation providing individualized organ dose estimates for NLST participant cohorts.

SU‐E‐I‐114: Clinical Ultrasound Transducer Degradation Effects on the Accuracy of Spectral Doppler Velocity Measurements

PURPOSE Ultrasound Doppler velocity measurements are routinely used to determine the severity of a stenosis in the carotid, renal or peripheral arteries. The objective of this study is to investigate and demonstrate the relationship between Doppler velocity measurements and transducer degradation conditions encountered in a clinical environment. METHODS Assessing transducer performance was accomplished using the First Call aPerio Test System transducer analyzer (Sonora Medical Systems, Longmont, CO). This system was used to conduct 1,145 semi-annual transducer assessments at 7 clinical sites from September 2007 to February 2012 as part of a comprehensive quality control program. The results were evaluated to determine the degree of transducer degradation encountered in the clinical environment. A Siemens Acuson S2000 (Siemens AG, Erlangen, Germany) ultrasound system was employed with the 1425A LE Doppler Flow System (Gammex, Middleton, WI) to determine Doppler velocity measurements. A transducer fixation device was fabricated to provide accurate, repeatable velocity measurements. Transducers with the most severe degradation were evaluated by comparing velocity measurements to those without defects. Using several matched transducer pairs, simulated failure modes were tested. The Doppler measured time-average mean (TAMn) and time-average maximum (TAMx) velocities were obtained and reported. RESULTS This investigation found that 4.5% of the transducers surveyed during this 5-year period of time failed at least one acceptance criteria. Many (346 or 30%) had at least one defect. Typical findings include dead elements, lens delamination, wire cuts, and capacitance shorts. Only the most severe transducer defects and degradation conditions resulted in a noticeable deviation in the velocity measurements. Simulated transducer degradation testing confirmed this finding. CONCLUSIONS The relationship between Doppler velocity measurements and transducer degradation conditions is limited, becoming significant for only the most severe degradation conditions. Based on our experience, this level of transducer degradation is rarely encountered in the clinical environment.

TU‐C‐W‐608‐01: Ultrasound QC Workshop

This workshop will provide attendees an opportunity to observe ultrasoundscanner operations and quality assurance procedures. A portable ultrasound unit and various ultrasound QC phantoms will be provided and used to demonstrate the QC procedures. A set of QC test procedures described in AAPM Ultrasound Task Group 1 Report (Medical Physics 1998;Vol 25: 1385–1406) will be presented, including display monitor fidelity, image uniformity, depth of visualization, horizontal and vertical distance accuracy, axial and lateral resolution, slice thickness, dead zone measurement. Demonstrations of test procedures and equipment will be performed by the instructors and industry representatives. Educational Objectives: 1. To learn the effect of parameter settings on various aspects of ultrasound imaging. 2. To observe the ultrasoundquality control test procedures for real‐time B‐mode units. 3. To become acquainted with various ultrasound QC phantoms.

60. Radiation dose reduction to medical staff during vertebroplasty: a review of techniques and methods to mitigate occupational dose

STUDY DESIGN Case crossover design was conducted. OBJECTIVES The purpose of the current study was to determine the radiation exposure level of operators performing fluoroscopically assisted vertebroplasty and to determine optimal techniques to reduce this exposure. SUMMARY OF BACKGROUND DATA The use of ionizing radiation to provide quality imaging during minimally invasive orthopedic procedures has dramatically increased. One such procedure, vertebroplasty, which is the percutaneous fixation of fractured vertebrae with polymethylmethacrylate, requires the use of ionizing radiation of biplanar fluoroscopy. The adverse effects of excessive radiation exposure to occupational personnel may not be realized for several years. METHODS Twelve months of occupational dose data for a single operator were evaluated and correlated to the modifications of practice habits implemented and shielding techniques used to reduce the operators exposure while maintaining adequate image quality. RESULTS Before the implementation of radiation-reduction procedures, the average whole-body dose per vertebroplasty procedure was 1.44 mSv/vertebrae, and the measured hand dose was 2.04 mSv/vertebrae. After implementation of radiation-reducing procedures and shielding techniques, the average whole-body dose per vertebroplasty procedure was 0.004 mSv/vertebrae, and the average hand dose was 0.074 mSv/vertebrae. Testing of the shielding device indicated a significant reduction in whole-body and hand doses. For the fluoroscopic modes investigated, the shielding used resulted in reductions ranging from 42.9% to 86.1%. CONCLUSION It is critical that operators performing vertebroplasty procedures have a fundamental understanding of radiation physics and radiation protection to minimize radiation exposure.