Jon A. Anderson

Radiation Doses in Interventional Radiology Procedures: The RAD-IR Study Part I: Overall Measures of Dose

PURPOSE To determine patient radiation doses for interventional radiology and neuroradiology procedures, to identify procedures associated with higher radiation doses, and to determine the effects of various parameters on patient doses. MATERIALS AND METHODS A prospective observational study was performed at seven academic medical centers. Each site contributed demographic and radiation dose data for subjects undergoing specific procedures in fluoroscopic suites equipped with built-in cumulative dose (CD) and dose-area-product (DAP) measurement capability compliant with International Electrotechnical Commission standard 60601-2-43. The accuracy of the dosimetry was confirmed by comprehensive measurements and by frequent consistency checks performed over the course of the study. RESULTS Data were collected on 2,142 instances of interventional radiology procedures, 48 comprehensive physics evaluations, and 581 periodic consistency checks from the 12 fluoroscopic units in the study. There were wide variations in dose and statistically significant differences in fluoroscopy time, number of images, DAP, and CD for different instances of the same procedure, depending on the nature of the lesion, its anatomic location, and the complexity of the procedure. For the 2,142 instances, observed CD and DAP correlate well overall (r = 0.83, P <.000001), but correlation in individual instances is poor. The same is true for the correlation between fluoroscopy time and CD (r = 0.79, P <.000001). The correlation between fluoroscopy time and DAP (r = 0.60, P <.000001) is not as good. In 6% of instances (128 of 2,142), which were principally embolization procedures, transjugular intrahepatic portosystemic shunt (TIPS) procedures, and renal/visceral artery stent placements, CD was greater than 5 Gy. CONCLUSIONS Most procedures studied can result in clinically significant radiation dose to the patient, even when performed by trained operators with use of dose-reducing technology and modern fluoroscopic equipment. Embolization procedures, TIPS creation, and renal/visceral artery stent placement are associated with a substantial likelihood of clinically significant patient dose. At minimum, patient dose data should be recorded in the medical record for these three types of procedures. These data should include indicators of the risk of deterministic effects as well as the risk of stochastic effects.

Radiation Doses in Interventional Radiology Procedures: The RAD-IR Study Part II: Skin Dose

PURPOSE To determine peak skin dose (PSD), a measure of the likelihood of radiation-induced skin effects, for a variety of common interventional radiology and interventional neuroradiology procedures, and to identify procedures associated with a PSD greater than 2 Gy. MATERIALS AND METHODS An observational study was conducted at seven academic medical centers in the United States. Sites prospectively contributed demographic and radiation dose data for subjects undergoing 21 specific procedures in a fluoroscopic suite equipped with built-in dosimetry capability. Comprehensive physics evaluations and periodic consistency checks were performed on each unit to verify the stability and consistency of the dosimeter. Seven of 12 fluoroscopic suites in the study were equipped with skin dose mapping software. RESULTS Over a 3-year period, skin dose data were recorded for 800 instances of 21 interventional radiology procedures. Wide variation in PSD was observed for different instances of the same procedure. Some instances of each procedure we studied resulted in a PSD greater than 2 Gy, except for nephrostomy, pulmonary angiography, and inferior vena cava filter placement. Some instances of transjugular intrahepatic portosystemic shunt (TIPS) creation, renal/visceral angioplasty, and angiographic diagnosis and therapy of gastrointestinal hemorrhage produced PSDs greater than 3 Gy. Some instances of hepatic chemoembolization, other tumor embolization, and neuroembolization procedures in the head and spine produced PSDs greater than 5 Gy. In a subset of 709 instances of higher-dose procedures, there was good overall correlation between PSD and cumulative dose (r = 0.86; P <.000001) and between PSD and dose-area-product (r = 0.85, P <.000001), but there was wide variation in these relationships for individual instances. CONCLUSIONS There are substantial variations in PSD among instances of the same procedure and among different procedure types. Most of the procedures observed may produce a PSD sufficient to cause deterministic effects in skin. It is suggested that dose data be recorded routinely for TIPS creation, angioplasty in the abdomen or pelvis, all embolization procedures, and especially for head and spine embolization procedures. Measurement or estimation of PSD is the best method for determining the likelihood of radiation-induced skin effects. Skin dose mapping is preferable to a single-point measurement of PSD.

Radiation doses in interventional radiology procedures: The RAD-IR study. Part III: Dosimetric performance of the interventional fluoroscopy units

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 units 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 units 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.

AAPM Task Group 108: PET and PET/CT Shielding Requirements

The shielding of positron emission tomography (PET) and PET/CT (computed tomography) facilities presents special challenges. The 0.511 MeV annihilation photons associated with positron decay are much higher energy than other diagnostic radiations. As a result, barrier shielding may be required in floors and ceilings as well as adjacent walls. Since the patient becomes the radioactive source after the radiopharmaceutical has been administered, one has to consider the entire time that the subject remains in the clinic. In this report we present methods for estimating the shielding requirements for PET and PET/CT facilities. Information about the physical properties of the most commonly used clinical PET radionuclides is summarized, although the report primarily refers to fluorine-18. Typical PET imaging protocols are reviewed and exposure rates from patients are estimated including self-attenuation by body tissues and physical decay of the radionuclide. Examples of barrier calculations are presented for controlled and noncontrolled areas. Shielding for adjacent rooms with scintillation cameras is also discussed. Tables and graphs of estimated transmission factors for lead, steel, and concrete at 0.511 MeV are also included. Meeting the regulatory limits for uncontrolled areas can be an expensive proposition. Careful planning with the equipment vendor, facility architect, and a qualified medical physicist is necessary to produce a cost effective design while maintaining radiation safety standards.

Strengthening the Argument for Rapid Brain MR Imaging: Estimation of Reduction in Lifetime Attributable Risk of Developing Fatal Cancer in Children with Shunted Hydrocephalus by Instituting a Rapid Brain MR Imaging Protocol in Lieu of Head CT

BACKGROUND AND PURPOSE: Children with shunted hydrocephalus have been undergoing surveillance neuroimaging, generally in the form of head CT, for evaluation of ventricular size. As the life expectancy of these children has improved due to better shunt technology and medical care, risks related to the ionizing radiation incurred during multiple head CT examinations that they are expected to undergo throughout their lifetime have become a concern. The purpose of this study is to estimate the LAR of developing fatal cancer due to head CT for ventricular size assessment in children with shunted hydrocephalus and to assess the impact of instituting a rapid brain MR imaging protocol in reducing radiation exposure. MATERIALS AND METHODS: Retrospective review of medical records yielded 182 patients who underwent neuroimaging for assessment of ventricular size. Available neuroimaging studies (head CT and rapid brain MR) were counted and annual neuroimaging frequency was calculated. It was assumed that these patients undergo a similar number of neuroimaging studies annually through 20 years of age. A risk estimate was calculated based on the BEIR VII report and effective doses obtained using the International Commission on Radiologic Protection Report 103 organ weighting factors. RESULTS: The mean annual neuroimaging study frequency was 2.1. Based on the average age of 1.89 years, it was assumed neuroimaging surveillance commences in the second year of life. LAR was calculated assuming that a patient undergoes neuroimaging in the form of head CT at this frequency (2/year) through 20 years of age. Assuming 2 scans are performed per year and the low-dose head CT protocol is used, approximately 1 excess lifetime fatal cancer would be generated per 230 patients; with standard head CT, there would be 1 excess lifetime fatal cancer per 97 patients. CONCLUSIONS: Children with shunted hydrocephalus are at increased risk of developing fatal cancer if they are to undergo surveillance using head CT. Implementation of a rapid brain MR imaging protocol with no radiation detriment will reduce this risk.

Surgeon education decreases radiation dose in complex endovascular procedures and improves patient safety

OBJECTIVE Complex endovascular procedures such as fenestrated endovascular aneurysm repair (FEVAR) are associated with higher radiation doses compared with other fluoroscopically guided interventions (FGIs). The purpose of this study was to determine whether surgeon education on radiation dose control can lead to lower reference air kerma (RAK) and peak skin dose (PSD) levels in high-dose procedures. METHODS Radiation dose and operating factors were recorded for FGI performed in a hybrid room over a 16-month period. Cases exceeding 6 Gy RAK were investigated according to institutional policy. Information obtained from these investigations led to surgeon education focused on reducing patient dose. Points addressed included increasing table height, utilizing collimation and angulation, decreasing magnification modes, and maintaining minimal patient-to-detector distance. Procedural RAK doses and operating factors were compared 8 months pre- (group A) and 8 months post- (group B) educational intervention using analysis of variance with Tukey pairwise comparisons and t-tests. PSD distributions were calculated using custom software employing input data from fluoroscopic machine logs. RESULTS Of 447 procedures performed, 300 FGIs had sufficient data to be included in the analysis (54% lower extremity, 11% thoracic endovascular aneurysm repair, 10% cerebral, 8% FEVAR, 7% endovascular aneurysm repair, 5% visceral, and 5% embolization). Twenty-one cases were investigated for exceeding 6 Gy RAK. FEVAR comprised 70% of the investigated cases and had a significantly higher median RAK dose compared with all other FGIs (P < .0001). There was no difference in body mass index between groups A and B; however, increasing body mass index was an indicator for increased RAK. PSD calculations were performed for the 122 procedures that focused on the thorax and abdomen (group A, 80 patients; group B, 42 patients). Surgeon education most strongly affected table height, with an average table height elevation of 10 cm per case after education (P < .0001). The dose index (PSD/RAK ratio) was used to track changes in operating practices, and it decreased from 1.14 to 0.79 after education (P < .0001). These changes resulted in an estimated 16% reduction in PSD. There was a trend toward a decrease in patient to detector distance, and the use of collimation increased from 25% to 40% (P < .001) for all cases; however, these did not result in a decrease in PSD. The number of cases that exceeded 6 Gy RAK did not change after education; however, the proportion of non-FEVAR cases that exceeded 6 Gy decreased from 40% to 20%. CONCLUSIONS Surgeon education on the appropriate use of technical factors during FGIs improved operating practice, reduced patient radiation dose, and decreased the number of non-FEVAR cases that exceeded 6 Gy. It is essential that vascular surgeons be educated in best operating practices to lower PSD; nonetheless, FEVAR remains a high-dose procedure.

New approaches in medical imaging using plastic scintillating detectors

Abstract A small animal imaging camera was built in our laboratory, using-fast plastic scintillating detectors ( τ = 2–4 ns) and position sensitive photomultipliers (Hamamatsu) digitized using flash ADCs. Pinhole collimators were used for 125 I imaging to achieve submillimeter resolution with scintillating plates of 28 mm radius and 1.5 mm thickness. A high resolution PET module was constructed with arrays of 1.0 mm diameter plastic scintillating fibers. The feasibility of high resolution imaging was demonstrated by the study of brain blood flow in a rat using 125 I IMP in single photon detection mode and with 64 Cu PTSM by using PET mode. Construction of single photon and positron emission tomographic imaging systems for small animals and subsequently for human imaging is in progress.

Indexing Severity of Diabetic Foot Infection With 99mTc-WBC SPECT/CT Hybrid Imaging

OBJECTIVE Management of diabetic foot infection (DFI) has been hampered by limited means of accurately classifying disease severity. New hybrid nuclear/computed tomography (CT) imaging techniques elucidate a combination of wound infection parameters not previously evaluated as outcome prognosticators. Our aim is to determine if a novel standardized hybrid image–based scoring system, Composite Severity Index (CSI), has prognostic value in DFI. RESEARCH DESIGN AND METHODS Masked retrospective 99mTc-white blood cell (WBC) single photon emission CT (SPECT)/CT image interpretation and independent chart review of 77 patients (101 feet) suspected of DFI-associated osteomyelitis at a large municipal hospital between January 2007 and July 2009. CSI scores were correlated with probability of favorable outcome (no subsequent amputation/readmission after therapeutic intervention) during median 342-day follow-up. RESULTS CSI ranged from 0–13. Receiver operating characteristic accuracy for predicting favorable outcome was 0.79 (optimal cutoff CSI, ≤2; odds ratio of therapeutic failure for CSI >2, 15.1 [95% CI 4.4–51.5]). CSI of 0 had a 92% chance of favorable outcome, which fell progressively to 25% as indices rose to ≥7. Image-based osteomyelitis versus no osteomyelitis assessment was less accurate than CSI at predicting outcome (P = 0.016). In patients with intermediate severity (CSI 3–6), treatment failure decreased from 68 to 36% when antibiotic duration was extended to ≥42 days (P = 0.026). CONCLUSIONS 99mTc-WBC SPECT/CT hybrid image–derived wound infection parameters incorporated into a standardized scoring system, CSI, has prognostic value in DFI.

Radiation-induced skin injury after complex endovascular procedures

BACKGROUND Radiation-induced skin injury is a serious potential complication of fluoroscopically guided interventions. Transient erythema occurs at doses of 2 to 5 Gy, whereas permanent epilation, ulceration, and desquamation are expected at doses above this level. Complex endovascular procedures (CEPs), such as fenestrated endovascular aortic aneurysm repair (FEVAR), are associated with high radiation doses, yet the prevalence of radiation-induced skin injury is unknown. We hypothesized that skin injury after these exposures is likely to be underrecognized and underreported. This study examined the frequency and severity of deterministic effects and evaluated patient characteristics that might predispose to radiation injury in CEP. METHODS CEP was defined as a procedure with a radiation dose ≥5 Gy (National Council on Radiation Protection and Measurements threshold for substantial radiation dose level [SRDL]). Radiation dose and operating factors were recorded for all CEPs performed in a hybrid room during a 30-month period. Patient medical records were retrospectively reviewed for evidence of skin injury. Patients were seen in follow-up daily until discharge and then at weeks 2 and 6, months 3 and 6, and 1 year. Phone interviews were conducted to determine the presence of any skin-related complaints. Peak skin dose (PSD) distributions were calculated for FEVARs with custom software employing input data from fluoroscopic machine logs. These calculations were validated against Gafchromic film (Ashland Inc, Covington, Ky) measurements. Dose was summed for the subset of patients with multiple procedures within 6 months of the SRDL event, consistent with Joint Commission recommendations. RESULTS Sixty-one CEPs reached a reference air kerma (RAK) of 5 Gy (50 FEVARs, six embolizations, one thoracic endovascular aortic repair, one endovascular aneurysm repair, one carotid intervention, and two visceral interventions). The patient cohort was 79% male and had a mean body mass index of 31. The average RAK was 8 ± 2 Gy (5.0-15.9 Gy). Sixteen patients had multiple CEPs within 6 months of the SRDL event, with a mean cumulative RAK of 12 ± 3 Gy (7.0-18.4 Gy). The mean FEVAR PSD was 6.6 ± 3.6 Gy (3.7-17.8 Gy), with a mean PSD/RAK ratio of 0.78. Gafchromic film dose measurements were not statistically different from PSD estimations, with a constant of proportionality of 0.99. Three patients were lost to follow-up before their first postoperative visit. No radiation skin injuries were found. CONCLUSIONS This study represents the largest analysis of deterministic skin injury after CEPs, and our results suggest that it is less frequent than expected and not increased in CEPs.

Contrast-detail characteristic evaluations of several display devices.

The contrast-detail characteristic of a display system is a powerful tool for evaluating displayed image quality. It takes into account the physical properties of the display, the psychophysical aspects of the observer, and the viewing conditions. It is a more sensitive measurement of the displayed image quality than a simple Society of Motion Picture and Television (SMPTE) pattern. Yet, it is relatively simple to measure and requires no special equipment or analysis tools. In this presentation, the results of the evaluation of several cathode ray tube (CRT) monitors and a digital projector will be presented. Contrast-detail characteristics of these display devices were measured under various gamma and display settings. The results show excellent intraobserver and interobserver variance (<1 step on the grayscale). Extraneous light, such as room lighting, affects the contrast threshold more severely at low background levels more than at high background. Gamma settings on graphics adapters affect the shapes of the contrast-detail curve for all display types. Gamma settings of approximately 2.0 result in a better contrast threshold for both high and low background brightness. The results show complex differences in contrast-detail characteristics for different display types. The digital projector display not only has significantly worse performance than CRT monitors, but also is affected more by extraneous light. High-brightness monitors with optimal monitor and graphics adapter settings have better performance than color or low-brightness monitors. However, under some settings, the performance of high-brightness monitors is not always better at all object sizes and background levels.