The rapidly increasing number of minimally invasive procedures performed in veterinary medicine has resulted in the increased use of fluoroscopy to guide diagnostic and therapeutic procedures. Fluoroscopy generates real-time radiographic images, which thereby facilitates procedures designed to minimize tissue trauma with the goal of lowering perioperative morbidity and mortality rates and shortening the hospitalization and recovery times.1 The increased use of fluoroscopy in veterinary medicine has resulted in a parallel increased risk of radiation exposure to patients, operators, and observers.
Radiation exposure associated with fluoroscopic procedures performed on human patients has been investigated and was found to be associated with deterministic skin effects (eg, erythema, moist desquamation, ulceration, depigmentation, hyperpigmentation, and scarring)2–8 in addition to an increased incidence of neoplasia.9–18 No studies have been conducted to determine the effects of radiation for canine patients undergoing fluoroscopic procedures. Investigators have evaluated the risk of excess radiation doses delivered to nearby tissues during CT planning for radiation treatments19 and adverse radiation effects associated with radiation treatment of cancer in dogs.7,20–22 Results indicated that radiation doses during CT were below recommended thresholds,19 but radiation treatment for several types of neoplasia in the head and neck areas can cause radiation injury to tissues adjacent to the radiation field22 (eg, the eyes) or within the radiation field21,22 (eg, oral mucous membranes and skin) of canine patients.8,19
In contrast to CT and radiation treatments, fluoroscopic procedures expose both patients and operators to cumulative doses of ionizing radiation23 in the forms of scatter and primary beam radiation.18,24 The versatility of fluoroscopy in veterinary medicine has resulted in numerous operators, many of whom have not been formally trained in radiobiology or radiography.1,25,26 Because of the extensive amounts of information about adverse radiation effects in human patients and the increased use of fluoroscopy in veterinary medicine, there is a definitive need for evaluation of the manner in which fluoroscopic procedures and the associated radiation exposure may affect veterinary patients, clinicians, and support staff.
To our knowledge, there have been no studies published on the evaluation of radiation exposure attributable to fluoroscopic procedures performed in veterinary medicine. The objective of the study reported here was to evaluate the radiation exposure resulting from fluoroscopy with mobile C-arm units during a variety of veterinary imaging-guided procedures and by various operators. We hypothesized that there would be differences in the fluoroscopic exposure attributable to the type of procedure and the operator.
Materials and Methods
Sample
Medical records of dogs and cats that underwent fluoroscopic procedures at the University of California-Davis (institution 1) and the University of Pennsylvania (institution 2) between August 2012 and October 2015 were identified. Institution, primary operator, type of procedure, and diagnosis were recorded for each case. The dose report produced by the C-arm unit was acquired for each procedure. Real-time measurement of the absorbed skin dose or operator dose was not performed. All dogs and cats for which a dose report was generated at the time of the fluoroscopic procedure were included in the study. Dogs and cats were excluded when a dose report was not available or the C-arm unit was used only to obtain a single image (eg, confirmation of the position of an enteral feeding tube or catheter).
Procedure categories
Fluoroscopic procedures were categorized on the basis of the type of intervention performed. Categories of fluoroscopic procedures were vascular, urinary, cardiac, gastrointestinal, orthopedic, and respiratory. Procedures were further subdivided into procedure type within a category.
Operator categories
Primary operators were categorized on the basis of specialty and advanced training. Interventional radiology-trained operators included operators who had received training via a fellowship in interventional radiology. Soft tissue surgeons were board-certified veterinary surgeons with a focus on soft tissue surgery or residents in a surgical training program. Orthopedic surgeons were board-certified veterinary surgeons with a focus on orthopedic surgery or residents in a surgical training program. Cardiologists were board-certified veterinary cardiologists or residents in a cardiology training program, and internists were clinicians who were board certified in veterinary internal medicine or residents in a training program in internal medicine.
Determination of radiation exposure
Dose reports from all 4 C-arm units were used to categorize the data into 2 groups: dynamic acquisition and digital exposure. Dynamic acquisition was defined as obtaining a series of continuous images. Time in minutes and exposure in milligrays were recorded for dynamic acquisition; the dose area product was recorded for the C-arm units for which this variable was available. Digital exposure was defined as a single radiographic image obtained with the fluoroscopic unit. Number of frames, time in minutes, and exposure in milligrays (and milligrays per centimeter when available) were recorded for digital exposures. Because exposure in milligrays was available for all dose reports, this value was used for comparison of radiation exposure.
Fluoroscopy time
Fluoroscopy time was recorded in minutes by each C-arm unit. Fluoroscopy time was categorized as dynamic fluoroscopy time or digital fluoroscopy time. Dynamic fluoroscopy time was defined as the amount of time spent obtaining series of images during a procedure. Digital fluoroscopy time was defined as the amount of time spent obtaining a single digital exposure (radiograph). Total digital fluoroscopy time was the amount of time spent obtaining a digital radiograph multiplied by the number of radiographic images obtained during that procedure. Total fluoroscopy time was defined as the sum of dynamic fluoroscopy time plus digital fluoroscopy time.
C-arm units
Data from 4 C-arm units were used in the study. Three C-arm unitsa-c were used at the University of California-Davis, and 1 C-arm unitd was used at the University of Pennsylvania. Additional procedures were performed at the University of California-Davis during this time using an additional C-arm unit. This unit did not generate a dose report; therefore, procedures performed on this unit were not included in the study.
Statistical analysis
Descriptive statistics were calculated. Categorical data were expressed as frequencies. To account for the fact the data were not normally distributed, continuous variables were expressed as median and range values. The Kruskal-Wallis test was used to compare continuous variables (fluoroscopy times and radiation exposure) among the categorical variables (procedure and operators), and the Dunn test was used to make pairwise comparisons. Values of P < 0.05 were considered significant. To control for potentially confounding variables, linear regression analysis was performed to evaluate the association between the continuous and categorical variables with total radiation dose. Two-way interactions among the main effects were investigated. An interaction term was retained when the P value was < 0.05. Univariate analysis was performed initially, and factors with a Wald test value of P < 0.20 were included in the model. Factors were retained in the model on the basis of a value of P ≤ 0.05 or when they were found to be a confounder (changed model coefficients by > 15%). All analyses were performed with a statistical software program.e
Results
Sample
Records review identified 378 fluoroscopic procedures. Eighteen procedures were excluded because fluoroscopy was used for the sole purpose of acquisition of a single image to confirm the position of a feeding tube or catheter. No procedures were excluded because of the lack of a dose report generated by the C-arm units. Thus, data for 360 fluoroscopic procedures were used for analysis in the study. There were 245 procedures performed at the University of Pennsylvania (institution 1) and 115 procedures performed at the University of California-Davis (institution 2). There were 148 (41%) urinary procedures, 66 (18%) respiratory procedures, 62 (17%) cardiovascular procedures, 43 (12%) vascular procedures, 37 (10%) orthopedic procedures, and 4 (1%) gastrointestinal procedures (Table 1).
Number of procedures in each category for 360 fluoroscopic procedures performed on dogs and cats at 2 academic institutions.
| No. of procedures | |||
|---|---|---|---|
| Category | Institution 1 | Institution 2 | Total |
| Vascular | |||
| PTCE | 10 | 10 | 20 |
| AVM embolization | 2 | 4 | 6 |
| Intra-arterial chemotherapy | 5 | 9 | 14 |
| Angiography | 0 | 3 | 3 |
| Total | 17 | 26 | 43 |
| Urinary | |||
| Ectopic ureter | 4 | 15 | 19 |
| Ureteral stent | 6 | 32 | 38 |
| SUB | 5 | 7 | 12 |
| Urethral stent | 1 | 21 | 22 |
| Cystourethrogram | 15 | 30 | 45 |
| Other | 1 | 11 | 12 |
| Total | 32 | 116 | 148 |
| Respiratory | |||
| Tracheal stent | 1 | 46 | 47 |
| Airway evaluation | 0 | 16 | 16 |
| NPS balloon or stent | 2 | 0 | 2 |
| Other | 1 | 0 | 1 |
| Total | 4 | 62 | 66 |
| Gastrointestinal | |||
| Colonic stent | 0 | 1 | 1 |
| Barium swallow | 0 | 1 | 1 |
| Esophageal balloon | 2 | 0 | 2 |
| Total | 2 | 2 | 4 |
| Cardiovascular | |||
| Patent ductus arteriosus | 9 | 6 | 15 |
| Pulmonary stenosis balloon | 4 | 12 | 16 |
| Pacemaker | 20 | 9 | 29 |
| Other | 1 | 1 | 2 |
| Total | 34 | 28 | 62 |
| Orthopedic | |||
| Sacroiliac luxation | 1 | 2 | 3 |
| Fracture fixation | 19 | 6 | 25 |
| MIPO | 0 | 1 | 1 |
| External fixation | 1 | 2 | 3 |
| Implant removal | 1 | 0 | 1 |
| Other | 4 | 0 | 4 |
| Total | 26 | 11 | 37 |
| Total | 115 | 245 | 360 |
AVM = Arteriovenous malformation. MIPO = Minimally invasive percutaneous osteosynthesis. NPS = Nasopharyngeal stenosis. PTCE = Percutaneous transvenous coil embolization. SUB = Subcutaneous ureteral bypass.
Fluoroscopy time
Total median fluoroscopy time for all procedures was 9.00 minutes (range, 0.05 to 85.30 minutes). Median digital fluoroscopy time for acquiring radiographic images for all procedures was 0.07 minutes (range, 0 to 1.11 minutes), and median dynamic fluoroscopy time for acquiring series of images for all procedures was 8.85 minutes (range, 0.05 to 84.70 minutes). Total median fluoroscopy time for vascular procedures (35.83 minutes; range, 5.63 to 85.13 minutes) was significantly (P < 0.001) longer than that for any other type of procedure (Table 2).
Median and range fluoroscopy time for each category of procedure for 360 fluoroscopic procedures performed on dogs and cats at 2 institutions.
| Fluoroscopy time (min) | ||
|---|---|---|
| Category | Median | Range |
| Vascular | 35.83* | 5.63–85.13 |
| Urinary | 8.02 | 0.30–73.7 |
| Respiratory | 8.59 | 1.10–24.90 |
| Gastrointestinal | 1.75 | 0.90–12.30 |
| Cardiac | 10.45† | 0.02–17.80 |
| Orthopedic | 1.63‡ | 0.05–22.20 |
Value differs significantly (P < 0.001), compared with the value for each of the other categories.
Value differs significantly (P = 0.03), compared with the value for each of the other categories.
Value differs significantly (P < 0.001), compared with the value for each of the other categories, except for gastrointestinal, for which there was no significant (P > 0.05) difference.
Interventional radiology-trained operators and cardiologists were associated with a significantly (P < 0.001) longer median fluoroscopy time (11.85 minutes [range, 0.57 to 85.10 minutes] and 10.45 minutes [range, 0.02 to 47.80 minutes], respectively) than that for any other type of operator. However, median fluoroscopy time did not differ significantly between interventional radiology-trained operators and cardiologists (Table 3).
Median and range fluoroscopy time for each category of operator for 360 fluoroscopic procedures performed on dogs and cats at 2 institutions.
| Fluoroscopy time (min) | ||
|---|---|---|
| Category | Median | Range |
| Interventional radiology-trained operator | 11.85* | 50.57–85.10 |
| Cardiologist | 10.45† | 0.02–47.80 |
| Internist | 5.60‡ | 1.50–12.20 |
| Soft tissue surgeon | 2.10 | 0.30–23.70 |
| Orthopedic surgeon | 1.71‡ | 0.05–22.20 |
Value differs significantly (P < 0.001), compared with the value for each of the other categories, except for cardiologists, for which there was no significant (P > 0.05) difference.
Value differs significantly (P = 0.002), compared with the value for each of the other categories, except for interventional radiology-trained operators, for which there was no significant (P > 0.05) difference.
Value differs significantly (P = 0.02), compared with the value for each of the other categories, except for soft tissue surgeons, for which there was no significant (P > 0.05) difference.
Radiation exposure
Vascular procedures and cardiovascular procedures were associated with a significantly (P < 0.001) higher median total radiation exposure than that for any other type of procedure. Median total radiation exposure was 137.00 mGy (range, 13.00 to 617.51 mGy) and 25.82 mGy (range, 0.30 to 287.45 mGy) for vascular procedures and cardiovascular procedures, respectively (Table 4).
Median and range radiation exposure for each category of procedure for 360 fluoroscopic procedures performed on dogs and cats at 2 institutions.
| Radiation exposure (mGy) | ||
|---|---|---|
| Category | Median | Range |
| Vascular | 137.00* | 13.00–617.51 |
| Urinary | 15.60† | 0.15–191.00 |
| Respiratory | 8.78‡ | 0.27–130.79 |
| Gastrointestinal | 7.09 | 0.60–9.90 |
| Cardiac | 25.82§ | 0.30–287.45 |
| Orthopedic | 2.27¶ | 0.14–74.33 |
Value differs significantly (P < 0.001), compared with the value for each of the other categories.
Value differs significantly (P ≤ 0.05), compared with the value for each of the other categories, except for vascular.
Value differs significantly (P < 0.001), compared with the value for each of the other categories, except for gastrointestinal and orthopedic, for which there was no significant (P > 0.05) difference.
Value differs significantly (P = 0.02), compared with the value for each of the other categories.
Value differs significantly (P < 0.001), compared with the value for each of the other categories, except for respiratory and gastrointestinal, for which there was no significant (P > 0.05) difference.
Median total radiation exposure was significantly (P < 0.001) higher for procedures performed by interventional radiology-trained operators (16.10 mGy; range, 0.44 to 617.50 mGy), cardiologists (25.82 mGy; range, 0.33 to 287.45 mGy), and internists (25.24 mGy; range, 3.58 to 185.79 mGy) than that for procedures performed by other operators. However, radiation exposure did not differ significantly among interventional radiology-trained operators, cardiologists, and internists (Table 5).
Median and range radiation exposure for each category of operator for 360 fluoroscopic procedures performed on dogs and cats at 2 institutions.
| Radiation exposure (mGy) | ||
|---|---|---|
| Operator | Median | Range |
| Interventional radiology-trained operator | 16.10* | 0.44–617.50 |
| Soft tissue surgeon | 4.07 | 0.15–131.50 |
| Orthopedic surgeon | 2.38 | 0.14–74.33 |
| Cardiologist | 25.82* | 0.33–287.45 |
| Internist | 25.24* | 3.58–185.79 |
Value differs significantly (P < 0.001), compared with the values for soft tissue surgeon and orthopedic surgeon.
Linear regression analysis of total radiation exposure
A significant (P < 0.001) interaction was detected between the contribution of dynamic fluoroscopy time to total radiation exposure on the basis of institution. As dynamic fluoroscopy time increased, total radiation exposure increased significantly more at institution 1 than at institution 2 (Figure 1). In addition to institution and dynamic fluoroscopy time, total fluoroscopy time (P < 0.001 for the univariate analysis) was included in the final model and retained as a confounder between dynamic fluoroscopy time and total radiation exposure.
Scatterplot of the interaction between dynamic fluoroscopy time and institution on the total radiation exposure for 360 fluoroscopy procedures performed on dogs and cats at 2 institutions (institution 1, gray squares and dashed line; institution 2, black triangles and solid line). Each symbol represents a fluoroscopic procedure, and the lines represent the line of fit. Dynamic fluoroscopy time was defined as the amount of time spent obtaining series of images during a procedure.
Citation: American Journal of Veterinary Research 80, 6; 10.2460/ajvr.80.6.558
Scatterplot of the interaction between dynamic fluoroscopy time and institution on the total radiation exposure for 360 fluoroscopy procedures performed on dogs and cats at 2 institutions (institution 1, gray squares and dashed line; institution 2, black triangles and solid line). Each symbol represents a fluoroscopic procedure, and the lines represent the line of fit. Dynamic fluoroscopy time was defined as the amount of time spent obtaining series of images during a procedure.
Citation: American Journal of Veterinary Research 80, 6; 10.2460/ajvr.80.6.558
Scatterplot of the interaction between dynamic fluoroscopy time and institution on the total radiation exposure for 360 fluoroscopy procedures performed on dogs and cats at 2 institutions (institution 1, gray squares and dashed line; institution 2, black triangles and solid line). Each symbol represents a fluoroscopic procedure, and the lines represent the line of fit. Dynamic fluoroscopy time was defined as the amount of time spent obtaining series of images during a procedure.
Citation: American Journal of Veterinary Research 80, 6; 10.2460/ajvr.80.6.558
Discussion
To our knowledge, the study reported here was the first in which radiation exposure and fluoroscopy time associated with fluoroscopic procedures were evaluated in veterinary medicine. Results indicated that median fluoroscopy time and median radiation exposure were significantly greater for vascular procedures than for any other procedure evaluated. Additionally, operators who routinely performed interventional procedures were associated with significantly greater exposure to radiation, and the institution where these procedures were performed had a significant impact on radiation exposure.
In the present study, vascular procedures performed with fluoroscopy were associated with a larger median radiation exposure than for any other procedure, which is similar to results for human medicine. In human patients, vascular procedures (eg, creation of a transjugular intrahepatic portosystemic shunt, embolization of aneurysms, and correction of arteriovenous malformations) have been classified as high-dose procedures.8 These procedures commonly exceed a radiation exposure dose of 2 Gy, which is the dose that has been identified by the US FDA as the limit above which radiation doses for the patient should be monitored and recorded.27 The highest median radiation exposure delivered to the dogs or cats during any procedure in the present study was 137 mGy.
The discrepancy in exposure between vascular procedures and other types of procedures may have been attributable to the complex nature of those procedures. Vascular procedures commonly require higher-level or more detailed fluoroscopic modes (eg, digital subtraction angiography) to provide a complete visual examination, which results in a higher dose of radiation delivered during these procedures.8,27,28 Investigation into techniques for lowering the dose of radiation to patients has revealed that the use of low-level fluoroscopic modes (eg, low-dose and pulsed modes) for repair of endovascular aneurysms can significantly reduce the radiation dose to patients.28–31
In the study reported here, interventional radiology-trained operators, internists, and cardiologists were associated with greater radiation exposure during procedures than were other operators. These operators are those who are more likely to perform fluoroscopically complex procedures (eg, endovascular or urologic procedures).32,33 In addition, because interventional radiology is a relatively new modality in veterinary medicine, even experienced operators may be attempting to perform new procedures and developing proficiency and efficiency, all of which can affect exposure and procedural times. Inexperienced or untrained operators in human medicine are associated with higher radiation doses.34–36 Knowledge of C-arm modes and settings and operator training programs that enhance the understanding of the principles of fluoroscopy can significantly reduce the exposed radiation dose.34–36
Linear regression analysis was performed to determine factors that influenced radiation exposure. This analysis revealed that dynamic time and institution were prominent factors with regard to exposure. Despite this association, fluoroscopy time correlates poorly with fluoroscopy dose, and measuring radiation dose on the basis of time is inaccurate.37,38 Radiation dose is affected by a multitude of variables, including angle of the beam,6 C-arm modes,29 collimator size, patient positioning, and backscatter.39,40 Therefore, it is conceivable that a shorter fluoroscopy time could be associated with a higher radiation dose than a longer fluoroscopy time when the C-arm mode associated with the higher dose is used for a short amount of time.
Interestingly, institution had a significant impact on radiation exposure. One reason for this finding is that one institution used only 1 C-arm unit, whereas the other institution used 3 C-arm units. The data collected were not adjusted for C-arm unit, such that it was extremely plausible that different units may have been responsible for the discrepancy in radiation exposure between institutions. A second explanation was revealed after a review of the dose reports from both institutions. One institution performed all of their procedures in pulsed mode, whereas the other institution performed most of their procedures in continuous mode. The institution that used continuous mode had consistently higher median radiation exposures associated with any given median fluoroscopy time than did the other institution, which exclusively used the pulsed mode. This finding supported the current concept that pulsed modes of fluoroscopy decrease the absorbed dose by 32%, compared with absorption for conventional (continuous) modes of fluoroscopy.29 Furthermore, when radiation exposure is compared during pulsed and continuous modes of fluoroscopy, pulsed modes reduce fluoroscopy time by 76% and radiation dose by 64%, compared with results for continuous modes.41 Although a pulsed mode may not be ideal for all procedures because of a reduction in image quality, results of the present study suggested that low-dose modes or pulsed mode should be considered as a means to decrease radiation exposure to both operators and patients, when possible.
It is important that the results of the present study be interpreted within the context of the study's limitations. One major limitation was the use of the radiation exposure emitted by a C-arm unit as a surrogate for dose received by a patient or operator. Real-time assessment of the actual dose was not performed. Patient dose is defined as the amount of energy absorbed by a patient, as opposed to exposure, which is defined as the amount of radiation produced by a radiation source.37 Radiation received by a patient is not uniformly distributed37; backscatter can increase dose rate by 10% to 40%, and dose can be affected by collimator size, patient positioning, instrumentation, and changes in beam energy.39 To accurately measure radiation dose of a patient, 4 dose metrics have been developed: fluoroscopy time, peak skin dose, reference dose, and kerma area product (or dose area product).37 The combination of these metrics takes into account the various aspects of the radiation dose received by a patient, including the dose absorbed by the skin versus the dose absorbed by the internal organs.37 A more accurate estimate through real-time dosimetry and use of these 4 dose metrics would be necessary to truly characterize the risk to patients.
A second limitation of the present study was that 4 C-arm units were used. Although all units could record total exposure and time, it was not possible to compare C-arm modes, collimation, magnification, digital subtraction angiography, and high-level fluoroscopy used in each procedure. Additionally, the units differed with regard to technology and modes of operation; some could be used on both high-dose and low-dose settings and in pulsed and continuous modes of fluoroscopy, whereas other units had limited modes that could be adjusted. Therefore, C-arm mode was not evaluated when determining total exposure, which had a substantial impact on the total amount of radiation emitted, as was indicated by the discrepancy between the continuous and pulse modes at the 2 institutions.
Another limitation was the association of operator type with radiation exposure because the study was performed at 2 veterinary teaching hospitals. We did not control for variations in operator experience and training because of the retrospective nature of the study. Because we were unable to record all operators or assistants involved or the role they had for a given procedure, it was not possible to compare exposure to personal dose over time by use of institutionally provided dosimeters.
To our knowledge, studies conducted to evaluate the amount of radiation exposure veterinary patients receive during fluoroscopic procedures have not been published. The study reported here was performed to acquire baseline information about potential radiation exposure associated with fluoroscopic procedures currently being performed in veterinary medicine. Gaining a preliminary understanding of potential radiation exposure during fluoroscopic procedures is an important first step to begin the discussion of safety protocols that should be established for both patients and operators. Results of the present study supported results of previous studies8,27,28 of humans that indicate an increase in radiation exposure with endovascular procedures. Analysis of results of the present study also revealed that there was substantial radiation exposure associated with fluoroscopic procedures in veterinary medicine, which indicates the need for future studies that directly measure by use of real-time dosimetry and chromographic film the radiation dose received by patients and operators. This study can serve as the foundation for further investigations into radiation exposure to both patients and operators during fluoroscopy use in minimally invasive image-guided veterinary procedures.
Acknowledgments
No financial support was received to conduct this study. The authors have no conflicts of interest to declare.
Presented in abstract form at the 2016 Veterinary Interventional Radiology and Interventional Endoscopy Society Meeting, Jackson Hole, Wyo, June 2016.
Footnotes
OEC 9800, General Electric Healthcare, Chicago, Ill.
9900 Elite, General Electric Healthcare, Chicago, Ill.
9900 VAS, General Electric Healthcare, Chicago, Ill.
Veradius, Philips Healthcare, Amsterdam, Netherlands.
Stata, version 13, StataCorp LLC, College Station, Tex.
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