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Surgeon education decreases radiation dose in complex endovascular procedures and improves patient safety
From the Southern Association for Vascular Surgery
Surgeon education decreases radiation dose in complex endovascular procedures and improves patient safety Melissa L. Kirkwood, MD,a Gary M. Arbique, PhD,b Jeffrey B. Guild, PhD,b Carlos Timaran, MD,a Jayer Chung, MD,a Jon A. Anderson, PhD,b and R. James Valentine, MD,a Dallas, Tex 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-todetector 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. (J Vasc Surg 2013;58:715-21.)
Modern vascular surgeons perform an ever increasing number of complex fluoroscopically guided interventions (FGIs),1-3 largely based on patient preference, decreased length of stay, and improved outcome.4-8 With the upsurge of FGIs, concern has grown regarding the harmful effects of radiation exposure delivered to both patient and From the Division of Vascular and Endovascular Surgery, Department of Surgery,a and the Division of Medical Physics, Department of Radiology,b University of Texas Southwestern Medical Center. Author conflict of interest: none. Presented at the Thirty-seventh Annual Meeting of the Southern Association for Vascular Surgery, Paradise Island, Bahamas, January 23-26, 2013. Reprint requests: Melissa L. Kirkwood, MD, UT Southwestern Medical Center, Professional Office Building 1, Ste 620, 5959 Harry Hines Blvd, Dallas, TX 75390-9157 (e-mail: [email protected]). The editors and reviewers of this article have no relevant financial relationships to disclose per the JVS policy that requires reviewers to decline review of any manuscript for which they may have a conflict of interest. 0741-5214/$36.00 Copyright Ó 2013 by the Society for Vascular Surgery. http://dx.doi.org/10.1016/j.jvs.2013.04.004
operator.9-11 Injury from radiation exposure can be classified as deterministic or stochastic. Deterministic effects result from a predictable dose-related response with a threshold below which the effect is unlikely to occur, such as cutaneous radiation injury and cataracts. Stochastic effects, such as the development of cancer, have a probability of occurrence that increases with dose but have a severity that is dose-independent.12 Reference air kerma (RAK) is a frequently utilized measurement to quantify the peak skin dose (PSD) and hence, risk of subsequent deterministic injury.13 Skin injury represents the most common form of deterministic injury, and associated risk factors include patient parameters, technical factors, the interventionalist’s knowledge and skill, location of the lesion, and case complexity.14,15 Patientrelated risk factors such as obesity and connective tissue disorders are difficult to mitigate. Case complexity also is challenging to influence, with more complex interventions requiring higher radiation exposures.13,16,17 Among the known risk factors for deterministic injury, technical factors 715
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are most modifiable by the operator and include magnification mode, collimation, angulation, and table position. Exposure can be further managed by the appropriate selection of acquisition frame rate and pulsed fluoroscopy mode. A best operating guideline has therefore been published to effect more widespread application of radiation-limiting behaviors in an effort to limit the severity of radiation exposure during FGIs.13 However, rates of adherence and the effect of educational interventions to improve guideline adherence are poorly described in the literature. Vascular surgery is entering an era of increasing case complexity and higher radiation exposure. In particular, endovascular repair of thoracoabdominal aortic aneurysms with fenestrated stent grafts (FEVAR) has been recognized to generate radiation exposures even higher than previously reported in complex cases such as cerebrovascular interventions and endovascular aneurysm repair (EVAR).15,18 In this context, we aimed to describe the association between inadequate adherence to published guidelines of technical factors and resulted high radiation exposure in complex procedures. We hypothesized that educational interventions can improve conformity to best operating practice and result in reduced radiation dose. METHODS A retrospective review of patients undergoing FGIs in the hybrid fluoroscopic operating suite (Allura FD20; Philips Healthcare, Andover, Mass) by the vascular surgery service at St. Paul’s University Hospital at the University of Texas Southwestern Medical Center in Dallas, Texas, between January 2011 and April 2012 was performed. Information from the associated Xcelera Picture Archiving and Communication System (PACS) system provided image sets, protocol type, start and stop time, and cumulative RAK for each procedure. An educational event, taught by university medical physicists, occurred in the beginning of September 2011, dividing procedures into two groups. Procedures performed 8 months prior to the education intervention (group A) were compared to procedures performed 8 months after the educational intervention (group B). Definition and calculation of RAK. RAK was used as the dosimetry quantification method to predict PSD.14,17 The RAK is the kinetic energy released in the medium at the interventional reference point, which is located 15 cm along the beam axis toward the focal spot from isocenter (Fig 1). The RAK offers an estimate of the air kerma (AK) at the patient’s skin and includes both fluoroscopic and angiographic exposures.19 System operation logs provided records detailing acquisition time, generator technique factors, operating mode factors, table height and gantry geometry parameters, and number of acquired image frames for X ray generator activation events. These event records were matched to their corresponding procedures. Because RAK measures dose at a fixed position on the beam axis, it does not account for actual patient positioning. Geometry factors such as changes in angulation can tend to spread dose or changes in table height may lead to under- or overestimates of AK at the patient.20
Fig 1. Interventional reference point. SID, Source-to-image distance.
Patient positioning, geometry factors, and dose conversion factors must be applied to the RAK to estimate skin dose.21 Patient exposure estimates were calculated based on the system log events. For each event, RAK was calculated from technique factors, beam filtration, and measurements of X-ray radiation output. Using this calculated RAK and event geometry parameters, AK maps corresponding to the posterior surface of a patient lying supine on the table pad were calculated using customized software (IDL; Excelis Visual Information Systems, Boulder, Colo). Dose conversion factors and measured beam attenuation corrections were applied to the procedure AK maps to estimate PSDs.21 The aforementioned calculations have been validated against Gafchromic film.22 Study design and procedural details. In accordance with institutional policy, patients with a fluoroscopy procedure RAK exceeding 6 Gy require a PSD investigation by a medical physicist. Investigated cases revealed fluoroscopy usage patterns in the hybrid suite that contributed to higher than expected PSDs. Consequently, surgeon education occurred, which was additional to the 1-hour annual online course required for fluoroscopic credentialing. The educational event consisted of informal instruction regarding good operating practices aimed at decreasing patient dose. Highlighted points included the importance of using elevated table height, tight collimation in place of magnification, gantry angulation to spread skin dose, minimal patient-to-detector distance, digital subtraction acquisition (DSA) runs sparingly, and lowest possible frame rates for both fluoroscopy and DSA runs.
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Fig 2. Case distribution (n ¼ 300). EVAR, Endovascular aneurysm repair; TEVAR, thoracic endovascular aneurysm repair.
Procedures were categorized by procedure type: lower extremity diagnostic and intervention (LED, LEI), atherectomy (ATH), cerebral vascular (CV), embolization procedure (Embo), visceral artery (VA), endovascular infra-renal aneurysm repair (EVAR), thoracic endovascular aneurysm repair (TEVAR), fenestrated TEVAR (FTEVAR), and fenestrated EVAR (FEVAR). Body mass index (BMI) was calculated for all cases. For procedures using abdominal protocols, a PSD was estimated using the above mentioned software, and the dose index (ratio of PSD to RAK)19 was calculated to quantify changes in fluoroscopic operating practices. Technical details of the procedure were left entirely at the discretion of the operating surgeons. Statistical analysis plan. Comparative statistical analyses of RAK levels between categories was performed using analysis of variance with Tukey pairwise comparisons. The effects of patient BMI and case category on RAK levels were analyzed with a general linear model at a statistical significant level of P ¼ .05. Pre- and post-fluoroscopic use patterns (table height, collimation, magnification modes, fluoroscopic frame rates, angulation) and dose index were compared using independent sample t-tests with a level of significance of 0.05. Bonferroni correction was used for multiple comparisons. Mean values and 95% confidence intervals were obtained. The distribution of dose was not normally distributed, and the data were more consistent with a log normal distribution similar to other studies reviewing FGIs13,15,23,24; therefore, medians were used for comparisons with 95% confidence intervals and a P value <.05 for significance. RESULTS Of 447 procedures performed during the study period, 300 cases were FGIs and had sufficient data (complete fluoroscopic logs) to be included in the analysis (Fig 2).
One hundred fifty-six patients were in group A and 144 patients were in group B. Lower extremity and CV exams were excluded from PSD calculations because significant translational table motion occurs in these cases, resulting in inaccurate PSD estimations. One hundred twenty-two studies that were focused primarily in the thorax and abdomen were further analyzed for PSD. In this thoracoabdominal subset of patients analyzed for PSD, 80 patients were in group A and 42 patients in group B. In terms of patient populations, there was no significant difference in patient BMI (group A, 27.9; group B, 27.2; P ¼ NS) between groups. BMI, however, was a statistically significant indicator of increased RAK in both groups (P ¼ .007). Twenty-one patients were investigated for reaching 6 Gy RAK. FEVAR comprised 70% of the 21 cases investigated and had significantly higher procedural RAK than all other FGIs performed, with a median RAK of 6.5 Gy (P < .0001; Fig 3). Degree of fenestration ranged from one to four vessels; however, there was no difference in RAK dose based on number of vessels fenestrated. There was no statistically significant difference in procedural RAK among the remaining groups (LED, 0.4 Gy; LEI, 0.5 Gy; ATH, 0.8 Gy; CV, 0.5 Gy; TEVAR, 0.9 Gy; Embo, 1.0 Gy; EVAR, 1.0 Gy; VA, 1.6 Gy; FTEVAR, 2.4 Gy). Operating factors following the educational event. The educational event most significantly affected table height. In group A, on average per case, the table height was 210 mm below isocenter, and after intervention the table height in group B was, on average, 107 mm below isocenter (P < .001). This resulted in an average elevation of 103 mm in table height after educational intervention (Fig 4). The table height to detector distance trended down in group B but did not reach significance (group A, 420 mm; group B, 410 mm; P ¼ .13). The use of
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Fig 3. Procedural reference air kerma (RAK). ATH, Atherectomy; CV, cerebral vascular; Embo, embolization procedure; EVAR, endovascular infrarenal aneurysm repair; FEVAR, fenestrated EVAR; FTEVAR, fenestrated TEVAR; LED, lower extremity diagnostic; LEI, lower extremity intervention; TEVAR, thoracic endovascular aneurysm repair; VA, visceral artery.
Fig 5. Dose index before and after the educational event. PSD, Peak skin dose.
index (PSD/RAK) decreased significantly after education. The ratio in group A was 1.14 and in group B was 0.79 (P < .0001; Fig 5). The estimated mean PSD decreased by 16% in group B compared with group A (P < .001). Investigated case distribution after educational event. The number of cases that exceeded 6 Gy RAK and triggered an internal investigation did not change between groups; however, the proportion of non-FEVAR cases that exceeded 6 Gy decreased from 40% in group A (4/10) to 20% (2/11) in group B (Fig 6, A and B). DISCUSSION
Fig 4. Table height before and after the educational event.
collimation increased from 25% of cases with any use of collimation in group A, to 40% of cases in group B with some degree of collimation (P < .001). There was no observable change in other operating factors including the use of magnification modes, gantry angulation, or change in percentage of time spent in low-dose fluoroscopy modes vs high-dose digital acquisitions. PSD following the educational event. There was no significant difference between the mean RAKs in groups A and B (1.4 Gy and 1.5 Gy). Additionally, in the thoracoabdominal subset of patients that was analyzed for PSD, there was no significant difference in mean RAK (1.9 Gy in group A, and 2.3 Gy for group B). However, the dose
Radiation-induced skin injury, in the form of transient erythema, has been reported to occur when a dose of 2 Gy is reached during FGIs, with the severity of injuries increasing with dose.25,26 As the number of endovascular procedures increases, it is essential that physicians know the risk factors for injury, including patient, procedural, and technical operating factors.12 Patient obesity is a risk factor for radiation injury, because higher radiation output is necessary to penetrate the excess soft tissue, and as a consequence, larger patients are exposed to higher levels of radiation compared with thinner subjects.27 Weiss et al found that obese patients undergoing EVAR had up to three times higher PSDs then patients with a normal BMI.28 Similarly, Maurel and colleagues demonstrated during EVAR, the median dose area product of obese patients is significantly increased compared with that of nonobese patients.29 Our results concur with the literature that increasing BMI is a risk factor for high radiation dose. Procedural characteristics that affect risk of skin injury include the location of the lesion, procedure type, and case complexity.14,15 Increased complexity results in increased patient dose.30,31 Atherectomy, CV interventions, embolization procedures, and EVAR have all been associated with high radiation doses.16,32 Fenestrated endovascular aneurysm repair has emerged as one of the
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Fig 6. Investigated cases for exceeding 6 Gy reference air kerma (RAK). A, Group A (n ¼ 10). B, Group B (n ¼ 11). Embo, Embolization procedure; EVAR, endovascular infrarenal aneurysm repair; FEVAR, fenestrated EVAR; TEVAR, thoracic endovascular aneurysm repair; VA, visceral artery.
highest dose FGIs. In a review of radiation exposure in endovascular aneurysm repair, the exposure was higher for branched and fenestrated grafts.33 Panuccio et al reported a median RAK of 6.3 Gy for fenestrated stent grafts, with three patients exceeding 15 Gy RAK,18 further supporting case complexity as a risk factor for increased dose. In our study, the median RAK values, as shown in Fig 3, are consistent with the literature, and FEVAR is significantly higher than all other FGIs. In addition to patient risk factors and case complexity, the appropriate use of operating factors as well as the interventionalist’s knowledge regarding best practice guidelines during fluoroscopy are major contributors to radiation dose. Adjustments like raising the fluoroscopic table, minimizing patient-to-detector distance, limiting fluoroscopy time and high-dose digital acquisition runs, and utilizing collimation and pulsed fluoroscopy, as well as fluoroscopy looping whenever possible and reducing magnification modes and steep gantry angulation can limit patient dose.34 RAK is the best indicator of PSD.13 It is much more accurate than fluoroscopy time and dose area product, which has a potential error of at least 30% to 40% when estimating absorbed skin dose.19,26 Nonetheless, the calculation of PSD requires numerous assumptions, including attenuation corrections and back-scatter factors. However, the use of the dose index to quantify changes in PSD helps control for these uncertainties. Application of many of these good operating practices results in decreases in patient skin dose but is not reflected in changes in RAK. In this study, the dose index was used to track changes in operating practices since it reflects changes in skin dose while controlling for factors such as BMI and case complexity. A dose ratio greater than one indicates that skin dose will be higher than the displayed RAK; this may occur with highly angulated views or low table heights. Conversely, a dose ratio less than one indicates that the displayed RAK overestimates PSD, which can occur because of a high table height or considerable beam movement.19 In this study, the dose index decreased to less than one after education, suggesting that through better operating practices, the RAK went from an underestimation to an overestimation of skin dose delivered.
Because of these adjustments in operating practices after education, the estimated mean PSD decreased by 16%. In our study, table height and source focal spot to image detector distance (SID) were both increased in group B. These changes are consistent with the good operating tenet, maximize table height and minimize SID to minimize patient dose. This operating practice increases RAK since modern fluoroscopy systems use automatic brightness control to maintain a constant radiation input at the detector to produce images of uniform quality.30 Any increase in SID results in increased output because radiation at the detector becomes less concentrated as the inverse square of the SID (ie, inverse square law).35 Because AK at the patient decreases at a faster rate than RAK increases, concurrently raising the table and detector results in a lower PSD. Therefore, minimizing the patientto-detector distance is important to reduce exposure. In our study, there was a trend toward decreasing patientto-detector distance after education, but it did not reach significance. Utilizing angulation to avoid prolonged exposure to a small tissue area has been recommended as good operating practice.12 However, this method does not always lower PSD.20 Angulation changes must be large enough to distribute dose over distinct nonoverlapping areas of the skin to decrease PSD. Craniocaudal angulation should never be used as a PSD reduction technique. As the c-arm is rotated along the craniocaudal axis, the source-to-skin distance is decreased, and the patient’s thickness along the central ray is increased, which leads to a higher RAK and therefore, a higher patient skin dose.20 In one review, more than 80% of the injuries occurred with the beam in a steeply angled orientation.35 In our study, there was no difference in angulation before or after education. Tight collimation avoids overlap between the X-ray fields on the patient’s skin and therefore improves the effectiveness of dose spreading techniques.36 The use of collimation in our study increased from 25% to 40% of cases with any use of collimation. This change, however, did not result in a decrease in PSD. Collimation is most effective in decreasing PSD when used in concert with changes in angulation since it helps avoid beam overlap.
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Radiation doses to patients from fluoroscopy will be lower when properly trained interventionalists operate the equipment. Outside of institutional fluoroscopy credentialing policies, little time is spent in formal education of physicians in radiation safety.37 This study demonstrates that directed education to vascular surgeons can lower PSD. Additionally, physician education can help eliminate outlier high-dose cases as observed in the composition of case types exceeding 6 Gy RAK before and after education. Invariably, complex FGIs, namely fenestrated stent grafts, will require greater exposures. Recognizing risk factors for radiation-induced skin damage, specifically case complexity and patient obesity, allows for adjustments in operating practices to lower PSD accordingly. The present study has several limitations, most notably its retrospective design. However, study bias was avoided since operators were unaware that RAK values would be analyzed. Five different vascular surgeons with different operating practices and varying levels of experience were included; additionally, UTSW Medical Center is a teaching institution, and therefore vascular fellows and residents participated in the cases, further contributing to significant variation. Additionally, no testing occurred to evaluate the amount of learning by each operator. Differences in case distribution between groups may account for some of the observed PSD change. The calculation of PSD requires numerous assumptions, including attenuation corrections and back-scatter factors; however, the use of the dose index to quantify changes in PSD helps control for these uncertainties. Case category-specific changes were not compared between groups due to insufficient sample size. In conclusion, keeping best operating practices in the forefront on every interventionalist’s mind is paramount to decreasing dose and improving patient safety. At our institution, we have integrated radiation safety lectures into our conference curriculum and expect to see additional lowering of PSD. Future goals include more consistent use of collimation and a reduced use of high-dose acquisition modes. AUTHOR CONTRIBUTIONS Conception and design: MK, GA, JG, JA, RJV Analysis and interpretation: MK, GA, JG, JA Data collection: MK, GA, JG, CT, JC, JA, RJV Writing the article: MK, GA, JG, JA Critical revision of the article: RJV, JC, CT Final approval of the article: MK, GA, JG, CT, JC, JA, RJV Statistical analysis: JG, GA Obtained funding: Not applicable Overall responsibility: MK REFERENCES 1. Bates MC, Aburahma AF. An update on endovascular therapy of the lower extremities. J Endovasc Ther 2004;11(Suppl 2):II107-27. 2. Chuter TA, Parodi JC, Lawrence-Brown M. Management of abdominal aortic aneurysm: a decade of progress. J Endovasc Ther 2004;11(Suppl 2):II82-95.
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3. Mozes G, Sullivan TM, Torres-Russotto DR, Bower TC, Hoskin TL, Sampaio SM, et al. Carotid endarterectomy in SAPPHIRE-eligible highrisk patients: implications for selecting patients for carotid angioplasty and stenting. J Vasc Surg 2004;39:958-65; discussion: 965-6. 4. Anderson PL, Gelijns A, Moskowitz A, Arons R, Gupta L, Weinberg A, et al. Understanding trends in inpatient surgical volume: vascular interventions, 1980-2000. J Vasc Surg 2004;39:1200-8. 5. Blankensteijn JD, de Jong SE, Prinssen M, van der Ham AC, Buth J, van Sterkenburg SM, et al. Two-year outcomes after conventional or endovascular repair of abdominal aortic aneurysms. N Engl J Med 2005;352:2398-405. 6. Ketteler ER, Brown KR. Radiation exposure in endovascular procedures. J Vasc Surg 2011;53(1 Suppl):35S-8S. 7. Perera GB, Lyden SP. Current trends in lower extremity revascularization. Surg Clin North Am 2007;87:1135-47; x. 8. Prinssen M, Verhoeven EL, Buth J, Cuypers PW, van Sambeek MR, Balm R, et al. A randomized trial comparing conventional and endovascular repair of abdominal aortic aneurysms. N Engl J Med 2004;351:1607-18. 9. Hirshfeld JW Jr, Balter S, Brinker JA, Kern MJ, Klein LW, Lindsay BD, et al. ACCF/AHA/HRS/SCAI clinical competence statement on physician knowledge to optimize patient safety and image quality in fluoroscopically guided invasive cardiovascular procedures: a report of the American College of Cardiology Foundation/American Heart Association/American College of Physicians Task Force on Clinical Competence and Training. Circulation 2005;111:511-32. 10. Klein LW, Miller DL, Balter S, Laskey W, Haines D, Norbash A, et al. Occupational health hazards in the interventional laboratory: time for a safer environment. J Vasc Interv Radiol 2009;20(7 Suppl):S278-83. 11. Stecker MS, Balter S, Towbin RB, Miller DL, Vano E, Bartal G, et al. Guidelines for patient radiation dose management. J Vasc Interv Radiol 2009;20(7 Suppl):S263-73. 12. Brown KR, Rzucidlo E. Acute and chronic radiation injury. J Vasc Surg 2011;53(1 Suppl):15S-21S. 13. NCRP. “Radiation dose management for fluoroscopically guided interventional medical procedures,” Report No. 168. Bethesda, MD: National Council on Radiation Protection and Measurements; 2010. 14. Bor D, Sancak T, Toklu T, Olgar T, Ener S. Effects of radiologists’ skill and experience on patient doses in interventional examinations. Radiat Prot Dosimetry 2008;129:32-5. 15. Miller DL, Balter S, Cole PE, Lu HT, Berenstein A, Albert R, et al. Radiation doses in interventional radiology procedures: the RAD-IR study: part II: skin dose. J Vasc Interv Radiol 2003;14:977-90. 16. Bannazadeh M, Altinel O, Kashyap VS, Sun Z, Clair D, Sarac TP. Patterns of procedure-specific radiation exposure in the endovascular era: impetus for further innovation. J Vasc Surg 2009;49:1520-4. 17. Killewich LA, Singleton TA. Governmental regulations and radiation exposure. J Vasc Surg 2011;53(1 Suppl):44S-6S. 18. Panuccio G, Greenberg RK, Wunderle K, Mastracci TM, Eagleton MG, Davros W. Comparison of indirect radiation dose estimates with directly measured radiation dose for patients and operators during complex endovascular procedures. J Vasc Surg 2011;53: 885-894 e1; discussion: 894. 19. Fletcher DW, Miller DL, Balter S, Taylor MA. Comparison of four techniques to estimate radiation dose to skin during angiographic and interventional radiology procedures. J Vasc Interv Radiol 2002;13: 391-7. 20. Pasciak AS, Jones AK. Does “spreading” skin dose by rotating the C-arm during an intervention work? J Vasc Interv Radiol 2011;22: 443-52; quiz 53. 21. Petoussi-Henss N, Zankl M, Drexler G, Panzer W, Regulla D. Calculation of backscatter factors for diagnostic radiology using Monte Carlo methods. Phys Med Biol 1998;43:2237-50. 22. Guild JB, Arbique G, Gallet JM, Blackburn TJ, Anderson JA. Filling the gap: using detailed machine parameters to refine skin dose calculations for fluoroscopic sentinel events. Med Phys 2011;38:3414. 23. Dauer LT, Thornton R, Erdi Y, Ching H, Hamacher K, Boylan DC, et al. Estimating radiation doses to the skin from interventional radiology procedures for a patient population with cancer. J Vasc Interv Radiol 2009;20:782-8; quiz 9.
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24. Miller DL, Balter S, Cole PE, Lu HT, Schueler BA, Geisinger M, et al. Radiation doses in interventional radiology procedures: the RAD-IR study: part I: overall measures of dose. J Vasc Interv Radiol 2003;14: 711-27. 25. Koenig TR, Wolff D, Mettler FA, Wagner LK. Skin injuries from fluoroscopically guided procedures: part 1, characteristics of radiation injury. AJR Am J Roentgenol 2001;177:3-11. 26. Walsh SR, Cousins C, Tang TY, Gaunt ME, Boyle JR. Ionizing radiation in endovascular interventions. J Endovasc Ther 2008;15:680-7. 27. Hymes SR, Strom EA, Fife C. Radiation dermatitis: clinical presentation, pathophysiology, and treatment 2006. J Am Acad Dermatol 2006;54:28-46. 28. Weiss DJ, Pipinos II, Longo GM, Lynch TG, Rutar FJ, Johanning JM. Direct and indirect measurement of patient radiation exposure during endovascular aortic aneurysm repair. Ann Vasc Surg 2008;22: 723-9. 29. Maurel B, Sobocinski J, Perini P, Guillou M, Midulla M, Azzaoui R, et al. Evaluation of radiation during EVAR performed on a mobile C-arm. Eur J Vasc Endovasc Surg 2012;43:16-21. 30. Killewich LA, Falls G, Mastracci TM, Brown KR. Factors affecting radiation injury. J Vasc Surg 2011;53(1 Suppl):9S-14S.
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31. Balter S. Capturing patient doses from fluoroscopically based diagnostic and interventional systems. Health Phys 2008;95:535-40. 32. Steele JR, Jones AK, Ninan EP. Quality initiatives: establishing an interventional radiology patient radiation safety program. Radiographics 2012;32:277-87. 33. Howells P, Eaton R, Patel AS, Taylor P, Modarai B. Risk of radiation exposure during endovascular aortic repair. Eur J Vasc Endovasc Surg 2012;43:393-7. 34. Mitchell EL, Furey P. Prevention of radiation injury from medical imaging. J Vasc Surg 2011;53(1 Suppl):22S-7S. 35. Koenig TR, Mettler FA, Wagner LK. Skin injuries from fluoroscopically guided procedures: part 2, review of 73 cases and recommendations for minimizing dose delivered to patient. AJR Am J Roentgenol 2001;177: 13-20. 36. Miller DL, Balter S, Noonan PT, Georgia JD. Minimizing radiationinduced skin injury in interventional radiology procedures. Radiology 2002;225:329-36. 37. Geise RA, O’Dea TJ. Radiation dose in interventional fluoroscopic procedures. Appl Radiat Isot 1999;50:173-84. Submitted Jan 30, 2013; accepted Apr 1, 2013.
Surgeon education decreases radiation dose in complex endovascular procedures and improves patient safety Melissa L. Kirkwood, MD,a Gary M. Arbique, PhD,b Jeffrey B. Guild, PhD,b Carlos Timaran, MD,a Jayer Chung, MD,a Jon A. Anderson, PhD,b and R. James Valentine, MD,a Dallas, Tex 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-todetector 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. (J Vasc Surg 2013;58:715-21.)
Modern vascular surgeons perform an ever increasing number of complex fluoroscopically guided interventions (FGIs),1-3 largely based on patient preference, decreased length of stay, and improved outcome.4-8 With the upsurge of FGIs, concern has grown regarding the harmful effects of radiation exposure delivered to both patient and From the Division of Vascular and Endovascular Surgery, Department of Surgery,a and the Division of Medical Physics, Department of Radiology,b University of Texas Southwestern Medical Center. Author conflict of interest: none. Presented at the Thirty-seventh Annual Meeting of the Southern Association for Vascular Surgery, Paradise Island, Bahamas, January 23-26, 2013. Reprint requests: Melissa L. Kirkwood, MD, UT Southwestern Medical Center, Professional Office Building 1, Ste 620, 5959 Harry Hines Blvd, Dallas, TX 75390-9157 (e-mail: [email protected]). The editors and reviewers of this article have no relevant financial relationships to disclose per the JVS policy that requires reviewers to decline review of any manuscript for which they may have a conflict of interest. 0741-5214/$36.00 Copyright Ó 2013 by the Society for Vascular Surgery. http://dx.doi.org/10.1016/j.jvs.2013.04.004
operator.9-11 Injury from radiation exposure can be classified as deterministic or stochastic. Deterministic effects result from a predictable dose-related response with a threshold below which the effect is unlikely to occur, such as cutaneous radiation injury and cataracts. Stochastic effects, such as the development of cancer, have a probability of occurrence that increases with dose but have a severity that is dose-independent.12 Reference air kerma (RAK) is a frequently utilized measurement to quantify the peak skin dose (PSD) and hence, risk of subsequent deterministic injury.13 Skin injury represents the most common form of deterministic injury, and associated risk factors include patient parameters, technical factors, the interventionalist’s knowledge and skill, location of the lesion, and case complexity.14,15 Patientrelated risk factors such as obesity and connective tissue disorders are difficult to mitigate. Case complexity also is challenging to influence, with more complex interventions requiring higher radiation exposures.13,16,17 Among the known risk factors for deterministic injury, technical factors 715
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are most modifiable by the operator and include magnification mode, collimation, angulation, and table position. Exposure can be further managed by the appropriate selection of acquisition frame rate and pulsed fluoroscopy mode. A best operating guideline has therefore been published to effect more widespread application of radiation-limiting behaviors in an effort to limit the severity of radiation exposure during FGIs.13 However, rates of adherence and the effect of educational interventions to improve guideline adherence are poorly described in the literature. Vascular surgery is entering an era of increasing case complexity and higher radiation exposure. In particular, endovascular repair of thoracoabdominal aortic aneurysms with fenestrated stent grafts (FEVAR) has been recognized to generate radiation exposures even higher than previously reported in complex cases such as cerebrovascular interventions and endovascular aneurysm repair (EVAR).15,18 In this context, we aimed to describe the association between inadequate adherence to published guidelines of technical factors and resulted high radiation exposure in complex procedures. We hypothesized that educational interventions can improve conformity to best operating practice and result in reduced radiation dose. METHODS A retrospective review of patients undergoing FGIs in the hybrid fluoroscopic operating suite (Allura FD20; Philips Healthcare, Andover, Mass) by the vascular surgery service at St. Paul’s University Hospital at the University of Texas Southwestern Medical Center in Dallas, Texas, between January 2011 and April 2012 was performed. Information from the associated Xcelera Picture Archiving and Communication System (PACS) system provided image sets, protocol type, start and stop time, and cumulative RAK for each procedure. An educational event, taught by university medical physicists, occurred in the beginning of September 2011, dividing procedures into two groups. Procedures performed 8 months prior to the education intervention (group A) were compared to procedures performed 8 months after the educational intervention (group B). Definition and calculation of RAK. RAK was used as the dosimetry quantification method to predict PSD.14,17 The RAK is the kinetic energy released in the medium at the interventional reference point, which is located 15 cm along the beam axis toward the focal spot from isocenter (Fig 1). The RAK offers an estimate of the air kerma (AK) at the patient’s skin and includes both fluoroscopic and angiographic exposures.19 System operation logs provided records detailing acquisition time, generator technique factors, operating mode factors, table height and gantry geometry parameters, and number of acquired image frames for X ray generator activation events. These event records were matched to their corresponding procedures. Because RAK measures dose at a fixed position on the beam axis, it does not account for actual patient positioning. Geometry factors such as changes in angulation can tend to spread dose or changes in table height may lead to under- or overestimates of AK at the patient.20
Fig 1. Interventional reference point. SID, Source-to-image distance.
Patient positioning, geometry factors, and dose conversion factors must be applied to the RAK to estimate skin dose.21 Patient exposure estimates were calculated based on the system log events. For each event, RAK was calculated from technique factors, beam filtration, and measurements of X-ray radiation output. Using this calculated RAK and event geometry parameters, AK maps corresponding to the posterior surface of a patient lying supine on the table pad were calculated using customized software (IDL; Excelis Visual Information Systems, Boulder, Colo). Dose conversion factors and measured beam attenuation corrections were applied to the procedure AK maps to estimate PSDs.21 The aforementioned calculations have been validated against Gafchromic film.22 Study design and procedural details. In accordance with institutional policy, patients with a fluoroscopy procedure RAK exceeding 6 Gy require a PSD investigation by a medical physicist. Investigated cases revealed fluoroscopy usage patterns in the hybrid suite that contributed to higher than expected PSDs. Consequently, surgeon education occurred, which was additional to the 1-hour annual online course required for fluoroscopic credentialing. The educational event consisted of informal instruction regarding good operating practices aimed at decreasing patient dose. Highlighted points included the importance of using elevated table height, tight collimation in place of magnification, gantry angulation to spread skin dose, minimal patient-to-detector distance, digital subtraction acquisition (DSA) runs sparingly, and lowest possible frame rates for both fluoroscopy and DSA runs.
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Fig 2. Case distribution (n ¼ 300). EVAR, Endovascular aneurysm repair; TEVAR, thoracic endovascular aneurysm repair.
Procedures were categorized by procedure type: lower extremity diagnostic and intervention (LED, LEI), atherectomy (ATH), cerebral vascular (CV), embolization procedure (Embo), visceral artery (VA), endovascular infra-renal aneurysm repair (EVAR), thoracic endovascular aneurysm repair (TEVAR), fenestrated TEVAR (FTEVAR), and fenestrated EVAR (FEVAR). Body mass index (BMI) was calculated for all cases. For procedures using abdominal protocols, a PSD was estimated using the above mentioned software, and the dose index (ratio of PSD to RAK)19 was calculated to quantify changes in fluoroscopic operating practices. Technical details of the procedure were left entirely at the discretion of the operating surgeons. Statistical analysis plan. Comparative statistical analyses of RAK levels between categories was performed using analysis of variance with Tukey pairwise comparisons. The effects of patient BMI and case category on RAK levels were analyzed with a general linear model at a statistical significant level of P ¼ .05. Pre- and post-fluoroscopic use patterns (table height, collimation, magnification modes, fluoroscopic frame rates, angulation) and dose index were compared using independent sample t-tests with a level of significance of 0.05. Bonferroni correction was used for multiple comparisons. Mean values and 95% confidence intervals were obtained. The distribution of dose was not normally distributed, and the data were more consistent with a log normal distribution similar to other studies reviewing FGIs13,15,23,24; therefore, medians were used for comparisons with 95% confidence intervals and a P value <.05 for significance. RESULTS Of 447 procedures performed during the study period, 300 cases were FGIs and had sufficient data (complete fluoroscopic logs) to be included in the analysis (Fig 2).
One hundred fifty-six patients were in group A and 144 patients were in group B. Lower extremity and CV exams were excluded from PSD calculations because significant translational table motion occurs in these cases, resulting in inaccurate PSD estimations. One hundred twenty-two studies that were focused primarily in the thorax and abdomen were further analyzed for PSD. In this thoracoabdominal subset of patients analyzed for PSD, 80 patients were in group A and 42 patients in group B. In terms of patient populations, there was no significant difference in patient BMI (group A, 27.9; group B, 27.2; P ¼ NS) between groups. BMI, however, was a statistically significant indicator of increased RAK in both groups (P ¼ .007). Twenty-one patients were investigated for reaching 6 Gy RAK. FEVAR comprised 70% of the 21 cases investigated and had significantly higher procedural RAK than all other FGIs performed, with a median RAK of 6.5 Gy (P < .0001; Fig 3). Degree of fenestration ranged from one to four vessels; however, there was no difference in RAK dose based on number of vessels fenestrated. There was no statistically significant difference in procedural RAK among the remaining groups (LED, 0.4 Gy; LEI, 0.5 Gy; ATH, 0.8 Gy; CV, 0.5 Gy; TEVAR, 0.9 Gy; Embo, 1.0 Gy; EVAR, 1.0 Gy; VA, 1.6 Gy; FTEVAR, 2.4 Gy). Operating factors following the educational event. The educational event most significantly affected table height. In group A, on average per case, the table height was 210 mm below isocenter, and after intervention the table height in group B was, on average, 107 mm below isocenter (P < .001). This resulted in an average elevation of 103 mm in table height after educational intervention (Fig 4). The table height to detector distance trended down in group B but did not reach significance (group A, 420 mm; group B, 410 mm; P ¼ .13). The use of
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Fig 3. Procedural reference air kerma (RAK). ATH, Atherectomy; CV, cerebral vascular; Embo, embolization procedure; EVAR, endovascular infrarenal aneurysm repair; FEVAR, fenestrated EVAR; FTEVAR, fenestrated TEVAR; LED, lower extremity diagnostic; LEI, lower extremity intervention; TEVAR, thoracic endovascular aneurysm repair; VA, visceral artery.
Fig 5. Dose index before and after the educational event. PSD, Peak skin dose.
index (PSD/RAK) decreased significantly after education. The ratio in group A was 1.14 and in group B was 0.79 (P < .0001; Fig 5). The estimated mean PSD decreased by 16% in group B compared with group A (P < .001). Investigated case distribution after educational event. The number of cases that exceeded 6 Gy RAK and triggered an internal investigation did not change between groups; however, the proportion of non-FEVAR cases that exceeded 6 Gy decreased from 40% in group A (4/10) to 20% (2/11) in group B (Fig 6, A and B). DISCUSSION
Fig 4. Table height before and after the educational event.
collimation increased from 25% of cases with any use of collimation in group A, to 40% of cases in group B with some degree of collimation (P < .001). There was no observable change in other operating factors including the use of magnification modes, gantry angulation, or change in percentage of time spent in low-dose fluoroscopy modes vs high-dose digital acquisitions. PSD following the educational event. There was no significant difference between the mean RAKs in groups A and B (1.4 Gy and 1.5 Gy). Additionally, in the thoracoabdominal subset of patients that was analyzed for PSD, there was no significant difference in mean RAK (1.9 Gy in group A, and 2.3 Gy for group B). However, the dose
Radiation-induced skin injury, in the form of transient erythema, has been reported to occur when a dose of 2 Gy is reached during FGIs, with the severity of injuries increasing with dose.25,26 As the number of endovascular procedures increases, it is essential that physicians know the risk factors for injury, including patient, procedural, and technical operating factors.12 Patient obesity is a risk factor for radiation injury, because higher radiation output is necessary to penetrate the excess soft tissue, and as a consequence, larger patients are exposed to higher levels of radiation compared with thinner subjects.27 Weiss et al found that obese patients undergoing EVAR had up to three times higher PSDs then patients with a normal BMI.28 Similarly, Maurel and colleagues demonstrated during EVAR, the median dose area product of obese patients is significantly increased compared with that of nonobese patients.29 Our results concur with the literature that increasing BMI is a risk factor for high radiation dose. Procedural characteristics that affect risk of skin injury include the location of the lesion, procedure type, and case complexity.14,15 Increased complexity results in increased patient dose.30,31 Atherectomy, CV interventions, embolization procedures, and EVAR have all been associated with high radiation doses.16,32 Fenestrated endovascular aneurysm repair has emerged as one of the
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Fig 6. Investigated cases for exceeding 6 Gy reference air kerma (RAK). A, Group A (n ¼ 10). B, Group B (n ¼ 11). Embo, Embolization procedure; EVAR, endovascular infrarenal aneurysm repair; FEVAR, fenestrated EVAR; TEVAR, thoracic endovascular aneurysm repair; VA, visceral artery.
highest dose FGIs. In a review of radiation exposure in endovascular aneurysm repair, the exposure was higher for branched and fenestrated grafts.33 Panuccio et al reported a median RAK of 6.3 Gy for fenestrated stent grafts, with three patients exceeding 15 Gy RAK,18 further supporting case complexity as a risk factor for increased dose. In our study, the median RAK values, as shown in Fig 3, are consistent with the literature, and FEVAR is significantly higher than all other FGIs. In addition to patient risk factors and case complexity, the appropriate use of operating factors as well as the interventionalist’s knowledge regarding best practice guidelines during fluoroscopy are major contributors to radiation dose. Adjustments like raising the fluoroscopic table, minimizing patient-to-detector distance, limiting fluoroscopy time and high-dose digital acquisition runs, and utilizing collimation and pulsed fluoroscopy, as well as fluoroscopy looping whenever possible and reducing magnification modes and steep gantry angulation can limit patient dose.34 RAK is the best indicator of PSD.13 It is much more accurate than fluoroscopy time and dose area product, which has a potential error of at least 30% to 40% when estimating absorbed skin dose.19,26 Nonetheless, the calculation of PSD requires numerous assumptions, including attenuation corrections and back-scatter factors. However, the use of the dose index to quantify changes in PSD helps control for these uncertainties. Application of many of these good operating practices results in decreases in patient skin dose but is not reflected in changes in RAK. In this study, the dose index was used to track changes in operating practices since it reflects changes in skin dose while controlling for factors such as BMI and case complexity. A dose ratio greater than one indicates that skin dose will be higher than the displayed RAK; this may occur with highly angulated views or low table heights. Conversely, a dose ratio less than one indicates that the displayed RAK overestimates PSD, which can occur because of a high table height or considerable beam movement.19 In this study, the dose index decreased to less than one after education, suggesting that through better operating practices, the RAK went from an underestimation to an overestimation of skin dose delivered.
Because of these adjustments in operating practices after education, the estimated mean PSD decreased by 16%. In our study, table height and source focal spot to image detector distance (SID) were both increased in group B. These changes are consistent with the good operating tenet, maximize table height and minimize SID to minimize patient dose. This operating practice increases RAK since modern fluoroscopy systems use automatic brightness control to maintain a constant radiation input at the detector to produce images of uniform quality.30 Any increase in SID results in increased output because radiation at the detector becomes less concentrated as the inverse square of the SID (ie, inverse square law).35 Because AK at the patient decreases at a faster rate than RAK increases, concurrently raising the table and detector results in a lower PSD. Therefore, minimizing the patientto-detector distance is important to reduce exposure. In our study, there was a trend toward decreasing patientto-detector distance after education, but it did not reach significance. Utilizing angulation to avoid prolonged exposure to a small tissue area has been recommended as good operating practice.12 However, this method does not always lower PSD.20 Angulation changes must be large enough to distribute dose over distinct nonoverlapping areas of the skin to decrease PSD. Craniocaudal angulation should never be used as a PSD reduction technique. As the c-arm is rotated along the craniocaudal axis, the source-to-skin distance is decreased, and the patient’s thickness along the central ray is increased, which leads to a higher RAK and therefore, a higher patient skin dose.20 In one review, more than 80% of the injuries occurred with the beam in a steeply angled orientation.35 In our study, there was no difference in angulation before or after education. Tight collimation avoids overlap between the X-ray fields on the patient’s skin and therefore improves the effectiveness of dose spreading techniques.36 The use of collimation in our study increased from 25% to 40% of cases with any use of collimation. This change, however, did not result in a decrease in PSD. Collimation is most effective in decreasing PSD when used in concert with changes in angulation since it helps avoid beam overlap.
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Radiation doses to patients from fluoroscopy will be lower when properly trained interventionalists operate the equipment. Outside of institutional fluoroscopy credentialing policies, little time is spent in formal education of physicians in radiation safety.37 This study demonstrates that directed education to vascular surgeons can lower PSD. Additionally, physician education can help eliminate outlier high-dose cases as observed in the composition of case types exceeding 6 Gy RAK before and after education. Invariably, complex FGIs, namely fenestrated stent grafts, will require greater exposures. Recognizing risk factors for radiation-induced skin damage, specifically case complexity and patient obesity, allows for adjustments in operating practices to lower PSD accordingly. The present study has several limitations, most notably its retrospective design. However, study bias was avoided since operators were unaware that RAK values would be analyzed. Five different vascular surgeons with different operating practices and varying levels of experience were included; additionally, UTSW Medical Center is a teaching institution, and therefore vascular fellows and residents participated in the cases, further contributing to significant variation. Additionally, no testing occurred to evaluate the amount of learning by each operator. Differences in case distribution between groups may account for some of the observed PSD change. The calculation of PSD requires numerous assumptions, including attenuation corrections and back-scatter factors; however, the use of the dose index to quantify changes in PSD helps control for these uncertainties. Case category-specific changes were not compared between groups due to insufficient sample size. In conclusion, keeping best operating practices in the forefront on every interventionalist’s mind is paramount to decreasing dose and improving patient safety. At our institution, we have integrated radiation safety lectures into our conference curriculum and expect to see additional lowering of PSD. Future goals include more consistent use of collimation and a reduced use of high-dose acquisition modes. AUTHOR CONTRIBUTIONS Conception and design: MK, GA, JG, JA, RJV Analysis and interpretation: MK, GA, JG, JA Data collection: MK, GA, JG, CT, JC, JA, RJV Writing the article: MK, GA, JG, JA Critical revision of the article: RJV, JC, CT Final approval of the article: MK, GA, JG, CT, JC, JA, RJV Statistical analysis: JG, GA Obtained funding: Not applicable Overall responsibility: MK REFERENCES 1. Bates MC, Aburahma AF. An update on endovascular therapy of the lower extremities. J Endovasc Ther 2004;11(Suppl 2):II107-27. 2. Chuter TA, Parodi JC, Lawrence-Brown M. Management of abdominal aortic aneurysm: a decade of progress. J Endovasc Ther 2004;11(Suppl 2):II82-95.
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3. Mozes G, Sullivan TM, Torres-Russotto DR, Bower TC, Hoskin TL, Sampaio SM, et al. Carotid endarterectomy in SAPPHIRE-eligible highrisk patients: implications for selecting patients for carotid angioplasty and stenting. J Vasc Surg 2004;39:958-65; discussion: 965-6. 4. Anderson PL, Gelijns A, Moskowitz A, Arons R, Gupta L, Weinberg A, et al. Understanding trends in inpatient surgical volume: vascular interventions, 1980-2000. J Vasc Surg 2004;39:1200-8. 5. Blankensteijn JD, de Jong SE, Prinssen M, van der Ham AC, Buth J, van Sterkenburg SM, et al. Two-year outcomes after conventional or endovascular repair of abdominal aortic aneurysms. N Engl J Med 2005;352:2398-405. 6. Ketteler ER, Brown KR. Radiation exposure in endovascular procedures. J Vasc Surg 2011;53(1 Suppl):35S-8S. 7. Perera GB, Lyden SP. Current trends in lower extremity revascularization. Surg Clin North Am 2007;87:1135-47; x. 8. Prinssen M, Verhoeven EL, Buth J, Cuypers PW, van Sambeek MR, Balm R, et al. A randomized trial comparing conventional and endovascular repair of abdominal aortic aneurysms. N Engl J Med 2004;351:1607-18. 9. Hirshfeld JW Jr, Balter S, Brinker JA, Kern MJ, Klein LW, Lindsay BD, et al. ACCF/AHA/HRS/SCAI clinical competence statement on physician knowledge to optimize patient safety and image quality in fluoroscopically guided invasive cardiovascular procedures: a report of the American College of Cardiology Foundation/American Heart Association/American College of Physicians Task Force on Clinical Competence and Training. Circulation 2005;111:511-32. 10. Klein LW, Miller DL, Balter S, Laskey W, Haines D, Norbash A, et al. Occupational health hazards in the interventional laboratory: time for a safer environment. J Vasc Interv Radiol 2009;20(7 Suppl):S278-83. 11. Stecker MS, Balter S, Towbin RB, Miller DL, Vano E, Bartal G, et al. Guidelines for patient radiation dose management. J Vasc Interv Radiol 2009;20(7 Suppl):S263-73. 12. Brown KR, Rzucidlo E. Acute and chronic radiation injury. J Vasc Surg 2011;53(1 Suppl):15S-21S. 13. NCRP. “Radiation dose management for fluoroscopically guided interventional medical procedures,” Report No. 168. Bethesda, MD: National Council on Radiation Protection and Measurements; 2010. 14. Bor D, Sancak T, Toklu T, Olgar T, Ener S. Effects of radiologists’ skill and experience on patient doses in interventional examinations. Radiat Prot Dosimetry 2008;129:32-5. 15. Miller DL, Balter S, Cole PE, Lu HT, Berenstein A, Albert R, et al. Radiation doses in interventional radiology procedures: the RAD-IR study: part II: skin dose. J Vasc Interv Radiol 2003;14:977-90. 16. Bannazadeh M, Altinel O, Kashyap VS, Sun Z, Clair D, Sarac TP. Patterns of procedure-specific radiation exposure in the endovascular era: impetus for further innovation. J Vasc Surg 2009;49:1520-4. 17. Killewich LA, Singleton TA. Governmental regulations and radiation exposure. J Vasc Surg 2011;53(1 Suppl):44S-6S. 18. Panuccio G, Greenberg RK, Wunderle K, Mastracci TM, Eagleton MG, Davros W. Comparison of indirect radiation dose estimates with directly measured radiation dose for patients and operators during complex endovascular procedures. J Vasc Surg 2011;53: 885-894 e1; discussion: 894. 19. Fletcher DW, Miller DL, Balter S, Taylor MA. Comparison of four techniques to estimate radiation dose to skin during angiographic and interventional radiology procedures. J Vasc Interv Radiol 2002;13: 391-7. 20. Pasciak AS, Jones AK. Does “spreading” skin dose by rotating the C-arm during an intervention work? J Vasc Interv Radiol 2011;22: 443-52; quiz 53. 21. Petoussi-Henss N, Zankl M, Drexler G, Panzer W, Regulla D. Calculation of backscatter factors for diagnostic radiology using Monte Carlo methods. Phys Med Biol 1998;43:2237-50. 22. Guild JB, Arbique G, Gallet JM, Blackburn TJ, Anderson JA. Filling the gap: using detailed machine parameters to refine skin dose calculations for fluoroscopic sentinel events. Med Phys 2011;38:3414. 23. Dauer LT, Thornton R, Erdi Y, Ching H, Hamacher K, Boylan DC, et al. Estimating radiation doses to the skin from interventional radiology procedures for a patient population with cancer. J Vasc Interv Radiol 2009;20:782-8; quiz 9.
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24. Miller DL, Balter S, Cole PE, Lu HT, Schueler BA, Geisinger M, et al. Radiation doses in interventional radiology procedures: the RAD-IR study: part I: overall measures of dose. J Vasc Interv Radiol 2003;14: 711-27. 25. Koenig TR, Wolff D, Mettler FA, Wagner LK. Skin injuries from fluoroscopically guided procedures: part 1, characteristics of radiation injury. AJR Am J Roentgenol 2001;177:3-11. 26. Walsh SR, Cousins C, Tang TY, Gaunt ME, Boyle JR. Ionizing radiation in endovascular interventions. J Endovasc Ther 2008;15:680-7. 27. Hymes SR, Strom EA, Fife C. Radiation dermatitis: clinical presentation, pathophysiology, and treatment 2006. J Am Acad Dermatol 2006;54:28-46. 28. Weiss DJ, Pipinos II, Longo GM, Lynch TG, Rutar FJ, Johanning JM. Direct and indirect measurement of patient radiation exposure during endovascular aortic aneurysm repair. Ann Vasc Surg 2008;22: 723-9. 29. Maurel B, Sobocinski J, Perini P, Guillou M, Midulla M, Azzaoui R, et al. Evaluation of radiation during EVAR performed on a mobile C-arm. Eur J Vasc Endovasc Surg 2012;43:16-21. 30. Killewich LA, Falls G, Mastracci TM, Brown KR. Factors affecting radiation injury. J Vasc Surg 2011;53(1 Suppl):9S-14S.
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31. Balter S. Capturing patient doses from fluoroscopically based diagnostic and interventional systems. Health Phys 2008;95:535-40. 32. Steele JR, Jones AK, Ninan EP. Quality initiatives: establishing an interventional radiology patient radiation safety program. Radiographics 2012;32:277-87. 33. Howells P, Eaton R, Patel AS, Taylor P, Modarai B. Risk of radiation exposure during endovascular aortic repair. Eur J Vasc Endovasc Surg 2012;43:393-7. 34. Mitchell EL, Furey P. Prevention of radiation injury from medical imaging. J Vasc Surg 2011;53(1 Suppl):22S-7S. 35. Koenig TR, Mettler FA, Wagner LK. Skin injuries from fluoroscopically guided procedures: part 2, review of 73 cases and recommendations for minimizing dose delivered to patient. AJR Am J Roentgenol 2001;177: 13-20. 36. Miller DL, Balter S, Noonan PT, Georgia JD. Minimizing radiationinduced skin injury in interventional radiology procedures. Radiology 2002;225:329-36. 37. Geise RA, O’Dea TJ. Radiation dose in interventional fluoroscopic procedures. Appl Radiat Isot 1999;50:173-84. Submitted Jan 30, 2013; accepted Apr 1, 2013.