Central Annals of Vascular Medicine & Research

Cite this article: Asthana A, Ashby B, Balter S, Kirtane AJ, Ekanem E, et al. (2016) Patient-Radiation-Exposure in Percutaneous Coronary and Peripheral Procedures and its Predictors in Peripheral Endovascular Intervention. Ann Vasc Med Res 3(2): 1031.

*Corresponding authorArushi Asthana, School of Public Health, Columbia University, USA, Email:

Submitted: 12 April 2016

Accepted: 08 June 2016

Published: 13 June 2016

ISSN: 2378-9344

Copyright© 2016 Asthana et al.

OPEN ACCESS

Keywords•Radiation dose•Air-kerma•Peripheral endovascular procedures•Percutaneous coronary intervention

Research Article

Patient-Radiation-Exposure in Percutaneous Coronary and Peripheral Procedures and its Predictors in Peripheral Endovascular InterventionArushi Asthana1*, Bernard Ashby2, Stephen Balter3, Ajay J. Kirtane4, Emmanuel Ekanem5, and William A. Gray4

1School of Public Health, Columbia University, USA2Department of Cardiology at Mount Sinai Medical Center, Columbia University, USA3Department of Radiology and Medicine, Columbia University, USA4Columbia University Medical Center/New York Presbyterian Hospital, Cardiovascular Research Foundation, USA5Department of Medicine, George Washington University School of Medicine, USA

Abstract

Aim: To identify predictors of patient-radiation-exposure measured as reference-point air-kerma (Kar) and kerma-area product (PKA), in peripheral endovascular procedures and to compare these measures in the percutaneous coronary and peripheral procedure groups.

Methods and results: Data included 164 peripheral angiographies with endovascular intervention (PA + EI), and 1200 percutaneous coronary procedures comprising 400 each of coronary angiographies (CA), percutaneous coronary interventions (PCI), and same-sitting angiography and intervention (CA+PCI), performed in the year 2008, at Columbia University Medical Center. Multiple linear-regression analysis was done to identify predictors of radiation in the peripheral procedure group. The ANOVA test with Tukey’s correction was employed to compare log-doses in all the four procedure groups.

Median (mean) Ka,r in milligray, was 1034 (1216) for CA, 2916 (3455) for PCI, 2806 (3246) for CA+PCI and 661 (1012) for PA+EI. Median (mean) PKA in Gy.cm2 was 67 (81) for CA, 174 (213) for PCI, 165 (207) for CA+PCI and 80 (138) for PA+EI. CA+PCI compared to PCI, did not employ significantly different doses of radiation. Within the PA+EI group, even with controls, each kilogram increase in weight was associated with a 1.26 % increase in Ka,r (CI: 0.54%, 1.99%; p-value = 0.0007) and a 1.75% increase in PKA (CI: 1.06%, 2.45%; p-value: < .0001), and women were exposed to 32.6% less Ka,r(CI: - 48.23%, -12.22%; p-value = 0.0037) and 34.33 % less PKA (CI: -48.90%, -15.61%; p-value = 0.0012).

Conclusions: Endovascular intervention associated patient-radiation-exposure is roughly comparable to that in a diagnostic coronary angiogram and is significantly less compared to coronary intervention. Within PA+EI, exposure differs by patient and procedural characteristics.

ABBREVIATIONS CA: Coronary Angiography; PCI: Percutaneous Coronary

Intervention; PA: Peripheral Angiography; EI: Endovascular Intervention; Ka,r: Reference-Point Air-Kerma; PKA: Kerma-Area Product; IVUS: Intravascular Ultrasound

INTRODUCTION Radiation-exposure to patients during the performance of

invasive vascular procedures emanates from both X-ray image acquisition (cine and DSA) and fluoroscopy [1] and is reported to vary by more than a factor of ten even for the same type of procedure [2]. Given this enormous variability [2-4], it is difficult to assess which combination of patient and procedure may reach a level of exposure that has a high probability of radiation injury. The use of patient-characteristics in explaining some of

the variability in radiation-dose can potentially provide a pre-procedural estimate of the dose, and thereby, the risk of the associated injury. Further, the use of procedural characteristics to account for some of the variability may help future research by identifying areas where dose-reduction strategies will be most effective.

Radiation-induced adverse effects broadly fall into deterministic and stochastic types. Deterministic effects include skin injury that may range from mild erythema to severe necrosis requiring a graft [5]. The metric of radiation found to be associated with deterministic-risk is the reference-point air-kerma (Ka,r) [6]. For an isocentric fluoroscope, the reference point is 15 cm from isocenter toward the X-ray tube. This point approximates the location of the patient’s skin for an abdominal procedure. The reference point moves with the gantry. Peak skin dose, PSD, can

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be calculated from Ka,r if the patient size and the movement of the gantry is known for the entire procedure. The patient is in jeopardy of deterministic injuries when PSD exceeds 5 Gy; the severity of injury increases with increasing PSD [6]. However, given biological susceptibilities, injuries may occur below this threshold and may not necessarily occur beyond it [7]. One to 3 weeks may pass before the injury becomes manifest. Physicians may wrongly attribute this injury to other causes [8]. Thus, skin-injuries are possibly both under-reported and under-diagnosed. PSD is correlated with Ka,r [9].

The stochastic side-effect of radiation, namely cancer, does not have a threshold dose for occurrence: risk increases proportionately with dose [6]. While Ka,r is reflective of skin-dose, kerma area product, or PKA, reflects the entire amount of energy delivered to the patient by the X-ray beam [10] and is associated with an increased lifetime risk of cancer.

We sought to identify factors that may predict radiation-exposure during the performance of peripheral endovascular procedures, in both Ka,r and PKA measures, and document radiation exposure alongside patient and procedural details. This is particularly important given the rapid advancements in techniques that allow operators to treat more complex lesions, employing greater radiation [11,12]. Another aim was to compare CA, PCI, CA+PCI and PA+EI procedure groups for significant differences in Ka,r and PKA measures of patient-radiation-exposure.

METHODSCase selection

Data from 204 consecutiveperipheral endovascular procedures carried out at Columbia/New York Presbyterian Hospital in the year 2008 was considered. Patients who also underwent a coronary procedure (n =11), had a peripheral procedure performed in more than one general anatomic region categorized as leg, abdomen and chest (n = 7) or had missing radiation data (n = 1) were excluded. Further, patients who had PA alone (n = 9) or EI alone (n = 13), were excluded and only those who underwent PA and EI in the same sitting (n =164), were considered.

Twelve hundred percutaneous coronary procedures performed in the year 2008 were selected to include four-hundred each of CA, PCI and CA+PCI. A random number was assigned to each of the eligible cases in each category. Those with the lowest 400 were selected for the study.

All procedures were performed using interventional fluoroscopes equipped with flat-panel image receptors, state-of-the-art dose management hardware and software and with integrated radiation dose displays. These systems conform to the IEC 60601-2-43 standard for interventional fluoroscopy.

As part of the quality program of our laboratory, dosimetry information is collected on all procedures performed. The data presented in this paper was retrospectively obtained from clinical records under an approved IRB protocol with a formal waiver of informed consent.

Statistics

All analyses were performed using SAS version 9.3 (SAS

Institute Inc., Cary, North Carolina). Detailed descriptive statistics are reported on the original scale for each type of procedure. Given the highly right-skewed nature of the outcome variable, models for dose prediction as well as procedure-wise dose comparisons, were based on log-transformed doses. The distribution of both Ka,r and PKA was log-normal. However, as explained shortly below, back-transformation enabled us to finally report predictive models on the original scale.

Predictive models for patient-radiation-exposure in peripheral endovascular procedures were built for both log Ka,r and log PKA using multiple linear regression. Variables, the individual main effects of which had a p-value of 0.1 or less, were entered into an initial model. Variables with p-values higher than 0.05 were successively removed to obtain the final model. Diagnostics of the final models for both measures of radiation were reassuring: residuals were normally distributed and there was no evidence of heteroskedasticity or of multicolinearity based on tolerance levels. Beta coefficients of the variables were exponentiated to obtain the ratio of the geometric mean of one group, to its comparison group, on the original scale. To further improve interpretability, this value was expressed as average percent change on the original scale, in switching from one group to another in the case of categorical variables, and for each unit increase, in case of continuous variables.

The peripheral-procedure dataset had missing values for 7 potential predictor variables, some of which were in the final model for both measures of radiation. The final predictive models were therefore based on fewer than the 164 observations. The number of observations for 4 out of 7 physicians was insufficient for statistical testing; therefore, only 3 were tested for significance of effect on dose. In 4 out of the 6 fluoroscopy units fewer than 10 procedures each, had been performed. We therefore combined observations of these four units to create a third group.

Procedure-wise dose comparisons employed the ANOVA test, and a Tukey post-hoc correction for multiple comparisons.

RESULTSTable (1) is a statistical description of the procedural details

and characteristics of patients who underwent the procedures (Table 2). summarizes additional details for the peripheral endovascular procedures.

Dose-comparisons

Descriptive statistics for Ka,r, PKA and fluoroscopy time for PA + EI and each type of coronary procedure are depicted in Figures (1-3) respectively and documented in (Table 3).

The ANOVA test with a post-hoc Tukey correction showed all pairwise comparisons of both log Ka,r and log PKA to be significantly different at the 0.05 level, except the PCI and CA + PCI comparison. Both the PCI and the CA + PCI groups were associated with significantly and substantially more log Ka,r and log PKA than either the CA or the PA + EI group. No significant difference, however, was observed in the mean log Ka,r or the mean log PKA for PCI compared to CA + PCI. PA + EI was associated with significantly less log Ka,r and significantly more log PKA compared to CA. This difference, however, was small: PA + EI and CA exposed patients to comparable radiation in our data.

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Table 1: Patient and Procedural Characteristics for Invasive Coronary and Peripheral Vascular Procedures.

Variable Coronary Procedures* N Peripheral Vascular Procedures† N

Age in years: Mean (SD) 65.63 (12.44) 1200 69.26 (12.29) 164

Males: N (%) 750 (62.5%) 1200 99 (60.37) 164

Weight in kilograms: Mean (SD) 83.09 (19.4) 1200 80.50 (17.56) 163

IVUS* used: N (%) 161 (13.42) 1200 12 (7.32) 164Number of Cine Runs: Range

Mean (SD)Median (IQR)

3 – 15220.32 (11.25)19 (11 – 26.5)

12004 – 62

18.42 (9.35)16 (12 – 23)

164

Volume of Contrast: RangeMean (SD)

Median (IQR)

20 – 870215.12 (128.17)190 (118 – 285)

120010 – 340.

115.20 (63.22)105 (70 – 150)

161

*Coronary procedures included 400 stand-alone angiographies, 400 stand-alone interventions and 400 same-sitting angiographies and interventions. †Peripheral procedures included here are only same-sitting angiography and intervention. Abbrevations: SD= Standard Deviation; IQR= Interquartile Range; IVUS=Intravascular Ultrasound

Table 2: Additional Patient and Procedural Characteristics for the Peripheral Endovascular Procedures*.

Variable Statistical description†

Patients with restenosis 24 (14.63)Patients with chronic total

occlusion 64 (39.02)

General anatomic region of procedure

ChestAbdomen

Leg

31 (18.90)23 (14.02)

110 (67.07)

Number of vascular territories involved

1>1

136 (82.93)28 (17.07)

Number of wires used1

>1Missing data

99 (60.37)57 (34.76)

8 (4.88)Number of balloons used

01

>1Missing data

21 (12.80)86 (52.44)56 (34.15)

1 (0.61)Number of times a balloon was

inflatedRange

Median (IQR)Missing data

0 – 543 (1 – 9)4 (2.43)

Total balloon inflation time in minutes

Mean (SD)Median (IQR)Missing data

203.45 (349.27)56.50 (10 – 238.5)

32 (19.51)

Stent placed 98 (59.76)

Atherectomy done 31 (18.90)

Performing physicianABCDEF

95 (57.93)36 (21.95)26 (15.85)3 (1.83)2 (1.22)2 (1.22)

Number of Fellows01

>1Missing data

26 (15.85)77 (46.95)58 (35.37)

3 (1.83)Fluoroscopy Unit

ABCDEF

212022299

*Only same-sitting angiography and intervention are included.†Categorical variables described as: number, (percentage).N=164, unless missing data stated [as number, (percentage)].Abbrevations: SD= Standard Deviation; IQR= Interquartile Range.

Predictors of Ka,r in peripheral-endovascular procedures

Table (4) summarizes the significance test of individual effects of variables on Log Ka,r for peripheral endovascular procedures. Beta co-efficients were exponentiated to allow for expression as average percent change in Karin switching from one group to another for categorical variables. For continuous variables, this signified the average percent change in Ka,r for each unit increase in the predictor variable (Table 5). is a summary of the final predictive model. We emphasize that the average percent change in radiation in switching from one group to another (for example in switching from the male to the female group) is obtained, and thus reported, on the original, untransformed scale. Therefore, this is to be interpreted plainly as X percent change in actual radiation doses in milligray in case of Ka,r and in Gy*cm2 in case of PKA, between the two groups.

Model diagnostics revealed a gross outlier which was removed and the univariate and multivariable analyses rerun. This final model was based on 129 peripheral endovascular procedures.

Ka,r measures of radiation for females, compared to males, were 32.6% less (CI: -48.23, -12.22; p-value = 0.0037) in the adjusted model and 47.6% less (CI: -60.81, -30.00; p-value < 0.0001) in the individual effects model. For each kilogram

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increase in weight, a 1.26% increase in Ka,r was observed (CI: 0.54, 1.99; p-value = 0.0007) in the adjusted model and a 1.93% increase (CI: 1.12, 2.77; p-value < 0.0001) was observed in the individual effects model.

Further, in the adjusted model, the use of stent was associated with a 47.69% increase in Ka,r (CI: 14.51, 90.53; p-value: 0.003). Each milliliter of contrast injected was associated with a 0.29% increase in Kar (CI: 0.06, 0.52; p-value: 0.0122). A small but significant decrease of 0.04% in Ka,r was observed for each minute increase in the total balloon inflation time (CI: -0.09, -0.01; p-value: 0.0026). Each minute of fluoroscopy increased Ka,r by 1.06% (CI: 0.2, 1.94; p-value: 0.0161). There was considerable variability in radiation exposure with change in fluoroscopy units at our center. The overall model explained 45.88% of the variability in radiation exposure to patients as measured in Ka,r during the performance of peripheral endovascular procedures.

Predictors of PKA in peripheral-endovascular procedures

Table (6) summarizes the univariate effects of variables on PKA in peripheral endovascular procedures (Table 7) is a summary of the final multiple linear regression model.

Compared to males, females were exposed to an average of 50.86% less PKA (CI: -63.12%, -34.52%; p-value < 0.0001) in the individual effects model and 34.33 % less PKA (CI: -48.90%, -15.61%; p-value = 0.0012) in the controlled model. The individual effect of each kilogram increase in weight was an average increase of 2.5% (CI: 1.72%, 3.30%; p-value <.0001) in PKA while its effect with other significant controls was a 1.75% (CI: 1.06%, 2.45%; p-value: <.0001) increase in PKA.

Further, in the controlled model, the use of stent increased PKA measures of radiation exposure by an average of 29.56% (CI: 1.57%, 65.28%; p-value = 0.0372). Each milliliter of contrast injected was associated with a 0.34% increase in PKA (CI: 0.12%, 0.56%; p-value = 0.0023). For every minute of fluoroscopy, PKA increased by 0.87% (CI: 0.04%, 1.70%; p-value = 0.038). Every minute of balloon inflation was associated with a 0.04% decrease in PKA (CI: -0.09%, -0.02%; p-value = 0.0008). PKA measures of radiation exposure varied greatly by fluoroscopy unit, even after significant controls.

The final model, based on 130 peripheral endovascular procedures and summarized in (Table 7), was significant with a p-value of <0.0001 and explained 49.21% of the variability in PKA measures of patient-radiation exposure.

Two additional regression analyses were done with only gender and weight in the model. These models, based on patient characteristics alone, explained 15.34% and 22.9% of the variability in Ka,r and PKA respectively.

DISCUSSIONWhile only a few studies have attempted to identify

predictors of patient radiation exposure during percutaneous coronary procedures [13-15], only two [16,17] to the best of our knowledge, have attempted the same for peripheral endovascular procedures. Radiation-dose data for EI is also scarce. The largest study evaluating radiation doses in interventional radiology

Figure 1 Descriptive statistics for Ka,r , PKA and fluoroscopy time.

Figure 2 Descriptive statistics for Ka,r , PKA and fluoroscopy time.

Figure 3 Descriptive statistics for Ka,r , PKA and fluoroscopy time.

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Table 3: Ka,r, PKA and Fluoroscopy Time for Percutaneous Peripheral and Coronary Procedures.

N Min Max Mean SD 10% 25% 50% 75% 90%

Ka,r(in milligray)

PA+EI 164 14 6340 1021 995 185 334 661 1431 2397

CA 400 141 7176 1216 819 460 718 1034 1478 2061

PCI 400 225 13361 3455 2208 1156 1851 2916 4492 6551

CA+PCI 400 246 14616 3246 1887 1373 1991 2806 4017 5713

PKA (in Gy.cm2)

PA+EI 164 8 883 138 152 26 44 80 169 332

CA 400 12 451 81 56 31 46 67 100 144

PCI 400 16 4140 213 236 66 109 174 256 375

CA+PCI 400 28 3322 207 220 83 117 165 247 339

Fluoroscopy Time in Minutes

PA+EI 164 6.0 103.4 28.9 18.5 11.2 15.2 23.9 35.6 56.5

CA 400 1.1 44.7 7.6 6.4 2.5 3.5 5.7 9.3 15.3

PCI 400 2.9 102.3 24.0 15.7 8.1 12.7 20.5 31.9 42.8

CA+PCI 400 3.1 122.4 20.0 13.7 8.2 11.3 16.2 24.8 36.5Abbrevations: SD= Standard Deviation; PA+EI= Peripheral Angiography with Endovascular Intervention; CA= Coronary Angiography; PCI= Percutaneous Coronary Intervention; CA+PCI= Coronary Angiography with Percutaneous Coronary Intervention.

Table 4: Univariate predictors of Ka,r in peripheral endovascular procedures.

Variable (reference comparison) β for LogKa,r

Average percent change in Ka,r inswitching from the

reference comparison(95% CI)

P-Value

Female (Male) -0.6467 -47.62 (-60.81, -30.00) <.0001

Age ( less by 1 year) 0.0040 0.40 (-0.81, 1.63) 0.5168

Weight ( less by 1 kg) 0.0192 1.93 (1.12, 2.77) <.0001

Restenosis: Yes (No) -0.4787 -38.04 (-59.19, -5.93) 0.0249

Total Occlusion: Present (Absent) 0.0211 2.13 (-24.92, 38.95) 0.8921General anatomic region

Thorax and neckAbdomen and pelvis(Lower extremity)

0.15420.4033 16.67 (-20.81, 71.92)

49.67 (-3.31, 131.71)0.43320.0702

IVUS used (Not used) 0.3316 39.31 (-21.46, 147.18) 0.2550

Atherectomy done (Not done) -0.0326 -3.20 (-34.00, 41.96) 0.8666

Stent placed (Not placed) 0.4808 61.73 (20.18, 117.65) 0.0017

Number of vascular territories: 1 (>1) -0.4017 -33.08 (-55.12, -0.22) 0.0487

Number of wires used: 1 (>1) -0.0378 -3.70 (-29.69, 31.88) 0.8126Number of balloons used

01

(>1)

0.40280.2025 49.60 (-8.24, 143.91)

22.44 (-11.86, 70.11)0.10560.2255

Number of balloon inflations (-1 inflation) -0.0097 -0.96 (-2.55, 0.64 ) 0.2366

Total balloon inflation time (-1 minute) -0.0005 -0.05 (-0.09, -0.005) 0.0296

Volume of Contrast (- 1 ml) 0.0059 0.59 (0.37, 0.81) <.0001

Number of Cine Runs 0.0218 2.20 (0.61, 3.82) 0.0068

Fluoroscopy minutes 0.0159 1.60 (0.82, 2.39) <.0001

Performing physician† : AB

(C)

-0.06950.02391 -6.72 (-39.16, 43.03)

2.41 (-37.88, 68.87)0.74820.9248

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Fellows in the procedure01

(>1)

0.11440.0382

12.12 (-43.26, 40.20)3.89 (-40.05, 43.23)

0.61800.8213

Fluoroscopy Unit : BC

(others)

0.15291.0288

16.52 (-23.65, 77.86)179.77 (61.50, 384.64) 0.4761

0.0003

*IVUS: Intravascular Ultrasound †3 physicians were compared

Table 5: Predictive Model for Ka,r in Peripheral Endovascular Procedures.

Variable (reference group) β for logKa,r

Average percent change in Ka,r in switching from the

reference group (95% CI)P-value

Female (Male) -0.3944 -32.59 (-48.23, -12.22) 0.0037

Weight (less by 1kg) 0.0126 1.26 (0.54, 1.99) 0.0007

Stent placed (Not placed) 0.3900 47.69 (14.51, 90.53) 0.0030

Total balloon inflation time (-1 minute) -0.0005 -0.04 (-0.09, -0.01) 0.0026

Contrast Volume (-1 ml) 0.0029 0.29 (0.06, 0.52) 0.0122

Fluoroscopy minutes 0.0106 1.06 (0.2, 1.94) 0.0161Fluoroscopy Unit:

BC

(Others)

0.20980.96670.0000

23.34 (-13.32, 75.53)162.93 (69.29, 308.32)

0.2414<.0001

N=129. Adjusted R-squared=45.88 %. P-value for the model <0.0001

Table 6: Univariate predictors of logPKA in peripheral endovascular procedures.

Variable (reference comparison) Beta for logPKA

Average percent change in PKA inswitching from the

reference comparison(95% CI)

P-Value

Female (Male) -0.7106 -50.86 (-63.12, -34.52) <.0001

Age (less by 1 year) 0.0005 0.05 (-1.16, 1.29) 0.9268

Weight (less by 1 kg) 0.0248 2.5 (1.72, 3.30) <.0001

General anatomic regionchest

abdomen(leg)

-0.02510.2575 -2.47 (-34.05, 44.19)

29.36 (-16.76, 101.08)0.89910.2506

Total Occlusion (vs. No) -0.0683 -6.60 (-31.37, 27.09) 0.6619

IVUS* Used (Not used) 0.3535 42.40 (-19.86, 153.07) 0.2264

Restenosis: Yes (No) -0.4299 -34.94 (-57.27, -0.96) 0.0450

Atherectomy done (not done) -0.0310 -3.05 (-33.97, 42.34) 0.8733

Stent placed (Not placed) 0.3733 45.25 (7.48, 96.32) 0.0154

Number of vascular territories: 1 (>1) -0.2840 -24.72 (-49.40, 11.99) 0.1600

Number of balloons used: 01

(>1)

0.47810.3066 61.30 (-0.94, 162.70)

35.87 (-2.04, 88.49)0.05460.0661

Number of balloon inflations -0.0119 -1.18 (-2.77, 0.41) 0.1446

Total balloon inflation time (-1 minute) -0.0005 -0.04 (-0.10, -0.01) 0.0133

Number of wires used: 1 (>1) 0.0008 0.08 (-26.51, 36.29) 0.9959

Number of Cine Runs 0.0150 1.51 (-0.09, 3.14) 0.0646

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Volume of Contrast (-1 ml) 0.0061 0.61 (0.40, 0.83) <.0001

Fluoroscopy minutes 0.0122 1.22 (0.43, 2.04) 0.0026

Performing physician† : AB

(C)

-0.04300.1872 -4.20 (-37.23, 46.19)

20.58 (-26.23, 97.17)0.84090.4528

Fellows in the procedure: 01

(>1)

0.1517-0.0006 16.38 (-26.22, 83.61)

-0.05 (-28.57, 39.82)0.51190.9970

Fluoroscopy Unit: BC

(Others)

0.71501.0537 104.41 (33.32, 213.73)

186.82 (64.37, 400.56)0.00120.0003

*IVUS: intravascular ultrasound † 3 physicians were compared

Table 7: Multivariate Predictors of PKA (in Gy.cm2) in Peripheral endovascular procedures.

Variable (reference comparison) Beta for logPKA

Average percent change in PKA inswitching from the

reference comparison(95% CI)

P-value

Female (Male) -0.4206 -34.33 (-48.90, -15.61) 0.0012

Weight (less by 1 kg) 0.0174 1.75 (1.06, 2.45) <.0001

Stent (No stent) 0.2590 29.56 (1.57, 65.28) 0.0372

Balloon inflation time (less by 1 minute) -0.0005 -0.04 (-0.09, -0.02) 0.0008

Contrast volume (less by 1 ml) 0.0034 0.34 (0.12, 0.56) 0.0023

Fluoroscopy time (less by 1 minute) 0.0086 0.87 (0.04, 1.70) 0.0380Fluoroscopy Unit: B

C(Others)

0.71510.9544 104.43 (45.91, 186.45)

159.71 (70.47, 295.71)<.0001<.0001

N=130. Adjusted R-squared=0.4921 P-value for the model <0.0001

procedures, the RAD-IR study, only recorded 77 procedures relevant to peripheral angiography [18].

Another study [19], the most comprehensive thus far, was able to show procedure specific radiation exposure in patients who had undergone endovascular interventions at a single center as well as differences in radiation exposure among endovascular interventions. The use of fluoroscopy time to estimate the amount of radiation dose delivered was a notable limitation of the aforementioned study. Factors such as beam intensity, beam energy, beam orientation, field size and distance from the skin can affect the delivered dose and are not accounted for by estimations based on fluoroscopy time.

We believe that this is the most detailed evaluation of radiation exposure to patients in endovascular intervention, employing the more accurate measures of radiation. In a separate analysis of this data we compared fluoroscopy minutes for the 4 procedure types and found PA+EI to be associated with significantly more fluoroscopy time than any of the 3 categories of coronary procedures, even though the direct dose metrics were much lower for PA+EI compared to PCI and CA+PCI, suggesting that fluoroscopy time is a poor indicator of patient-radiation exposure. In the study carried out by Segal et al., [17] the subgroup that employed the most radiation, namely pelvic intervention, also involved the least fluoroscopy time.

Factors that play into determining how much radiation the patient will eventually receive are related to characteristics intrinsic to the patient, procedure, equipment, and the operator [13,20,21]. All three interventionists at our center were highly experienced and did not employ significantly different doses for either measure of radiation; the presence or number of fellows also did not affect patient radiation exposure.

We did not observe differences in radiation between the PCI-only the CA+PCI groups. It is likely that procedures deemed more complex were deferred after an initial angiogram and the expected small increase in radiation from angiography in the CA+PCI group was matched in the PCI-only group by increased radiation from greater procedural complexity. The PCI group was indeed associated with greater mean and median doses in both radiation-measures, though the difference was insignificant.

The sample size in our study may have been small to detect some associations. In one study, the performance of atherectomy was associated with increased radiation [19]. However, we did not find it to significantly affect patient-radiation exposure during the performance of peripheral endovascular procedures. Unlike Segal et al., [17] we did not find anatomic location to affect radiation dose. However, our anatomic data did not classify procedures above and below the knee separately. Combining some fluoroscopy units to obtain an adequate sample size

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may have resulted in an unreliable effect-size for this variable. Nonetheless, the inclusion of this variable served as an important control.

As of 2016, radiation-exposure at our center stands much reduced compared to the year 2008. However, this is not likely to impact the influence of independent variables on radiation-dose, and therefore, dose-predictive modeling. We hope to extract data over the recent years and analyze how it compares to this data, in subsequent studies.

CONCLUSIONWhile we could not readily identify reasons for less radiation

exposure in females undergoing PA+EI, possible explanations may be under treatment of women relative to men or gender related differences in the nature of the disease. Though height was not an included variable in our analysis, on account of missing observations that would shrink the sample size further, we did control for height in preliminary analyses and found the gender-radiation association to persist with both height and weight controlled for.

We were able to identify both patient and procedural details that explained a large part of the variability in patient-radiation-exposure in our data. Given the evolving nature of the field and the still unknown sources of variability, further research and continued dose-documentation are necessary.

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