Step back from the patient: Reduction of radiation dose to the operator by the systematic use of an automatic power injector for contrast media in an interventional angiography suite

Abstract

Background

During arterial interventional procedures, power injectors allow the operator to step back from the patient or exit the angiography suite during digital subtraction angiography (DSA) acquisitions. Increasing the distance to the radiation source reduces exposure to the operator and staff.

Purpose

To systematically investigate the effect of increasing the distance between the radiation source and the operator during DSA acquisitions in a daily clinical setting, regarding radiation exposure to the operator and patient, as well as the duration of the procedure using a power injector to deliver contrast media.

Material and Methods

Patients scheduled for arterial interventional procedures in the pelvis or lower extremities were consecutively included. In phase one (duration 6 weeks, 44 patients) contrast media were injected manually. In phase two (duration until the total dose area product [DAP] was equal to phase 1, 41 patients) the operator used a power injector and exited the suite whenever possible. Patient, procedure, and examination data were recorded. Collective dose to the operator's collar, lead apron, and hands was recorded using thermo luminescent dosimetry (TLD).

Results

Our results showed a dose reduction of 50% to the operator's hands, lead apron, and thyroid collar when using a power injector during DSA, with no significant increase in DAP or procedure time when performing pelvic procedures. For lower extremity procedures there was a small but significant increase in procedure time and DAP. Pelvic procedures yielded substantially higher DAP than lower extremity procedures during both phases.

Conclusion

Utilization of a power injector, thus allowing the operator to step back from the patient, facilitates a radiation dose reduction to the operator of approximately 50% with no significant increase in patient dose or procedure time during pelvic procedures.

Keywords

Vascular angiography occupational/environmental hazards radiation safety arteries angioplasty

Operators of interventional angiography equipment are exposed to ionizing radiation. The magnitude of this can vary according to operator, technique, and procedures performed (1–3). Several authors have shown that prolonged and additive exposure to ionizing radiation can lead to radiation damage such as cataracts (4, 5). In addition every exposure to ionizing radiation is assumed to increase the risk of developing cancer (4, 6). Therefore, international guidelines (7, 8) encourage the use of the least amount of radiation reasonably achievable; i.e. to act in accordance with the ALARA principle. The most important measures medical professionals can employ to ensure optimal radiation protection are to minimize exposure, increase the distance to the radiation source and apply appropriate shielding (8–12). State of the art equipment facilitates the minimization of exposure, due to efficient detectors, collimation, and pulsed radiation (13). Shielding is commonly applied by wearing lead aprons and collars in addition to movable lead barriers (10, 14). During digital subtraction angiography (DSA), modern angiographic equipment achieves visualization of the circulatory system in great detail by employing a serial radiographic mode (record mode), using substantially higher dose rates than what is used during fluoroscopic operation (fluoro mode). Using a power injector allows the operator to increase the distance from the patient during these acquisitions, as scattered radiation from the patient accounts for almost all of the exposure to the operator (1, 8, 14).

During diagnostic angiography most radiologists use a power injector to achieve good image quality through precise control of volume and pressure of the contrast media. As diagnostic angiography has been replaced by computed tomography angiography (CTA) and magnetic resonance angiography (MRA), interventional arterial procedures in our institution were being performed with predominantly hand injections, both for fluoroscopy and DSA; other studies report the same practice (15, 16).

The purpose of this study was to assess the effects on radiation exposure to the primary operator and patient, as well as on the procedural time if the operator applied systematic use of a power injector, enabling the primary operator to step back, or leave the room during acquisition of the digital subtraction angiography (DSA) series during interventional arterial procedures in the pelvis and lower extremities.

Material and Methods

The study was designed as a clinical interventional study without alteration in patient selection or pre-procedural workup from our usual clinical practice. Patients scheduled for arterial interventional procedures in the pelvic area or in the lower extremities were included. During the six weeks of phase one, the operator would continue the practice of injecting contrast media by hand, standing next to the patient. In phase two, contrast injections during DSA were performed using a power injector (Mark V ProVis, Medrad, Warrendale, PA, USA), whenever possible, either through a diagnostic catheter or by the sideport of the introducer.

Phase one (control group) included 44 patient procedures, phase two was completed at 41 patient procedures when the total dose area product (DAP) of phase one was reached, in order to get equal potential exposure to the primary operator. The following parameters were recorded: anatomical area of the procedure; number of contrast injections for DSA; DAP and exposure time for both fluoro and record mode; and operation time, defined as minutes from skin anesthesia to vessel closure. During phase one, all injections (n = 230) were done manually; during phase two 208 of 213 injections were done using a power injector. Patient characteristics, number of procedures, anatomical regions, and number of contrast injections per procedure during the two phases are shown in Table 1.

Table 1
Patient and examination data in phase one (n = 44) and two (n = 41). Comparison of ratios and medians with 95% confidence intervals

Phase one Phase two

Ratio Median 95% CI Ratio Median 95% CI P value

Sex (Male/Female) 18/26 23/18 0.12*

Anatomic area of procedure (Low. ex./Pelvis) 23/21 19/21 0.41*

Age (years) 73.5 63.0–78.0 70.0 64.0–75.0 0.91^†

Height (cm) 168 165–174 171 169–174 0.35^†

Weight (kg) 73.5 64.0–81.0 76.5 69.0–80.0 0.54^†

BMI (kg/m²) 24.0 22.2–25.9 25.1 24.2–27.4 0.17^†

Injections (n) 5 3–6 4 3–6 0.94^†

Fishers exact test

^†Mann – Whitney test

Low. Ex. = Lower extremities, BMI = body mass index

During the two phases, the four interventional radiologists of our department shared one single set of protection apron and collar (Scanflex Medical AB, Täby, Sweden) equipped with Harshaw TLD-100H two-element dosimeters (Harshaw/Bicron, Solon, OH, USA) (17) outside and inside the apron in chest level. In addition, Harshaw DXT-RAD TLD-100 dosimeters (18) were worn outside the apron at knee level, outside the collar at thyroid level and inside the apron at both left and right axillar level and on the middle finger of left and right hand. The Harshaw TLD-100H two element dosemeter contains two TLD chips: one for measuring dose near the surface (H0.07) and one for measuring dose approximately 10 mm inside the subject (H10). If two radiologists were working together in the laboratory, the dosimeters were worn by the primary operator. The contrast media injected by hand contained 300 mg/mL iodine (Iomeprol, Bracco, Milan, Italia), while the contrast media injected automatically contained 200 mg/mL iodine (Iomeprol) in order to compensate for an expected slight increase in injected volume of contrast media.

The laboratory set-up was an angiography suite (Innova; GE Healthcare, Milwaukee, WI, USA), with an under-the-table mounted X-ray tube, 40 × 40 cm flat panel detector, lead drape to the floor, and a 30-cm high lead shielding screen mounted on the table. In addition there is a movable ceiling mounted transparent lead screen with lead fringes. All these are regularly used. All radiologists wore personal leaded glasses. Vessel puncture was usually done by ultrasound guidance or by palpating the vessel, not by fluoroscopic guidance. All procedures were performed from the common femoral artery access.

Reported TLD dosimeter reading (µSv) to equivalent dose (mSv) calibration curve was obtained by exposing a set of four Harshaw DXT-RAD TLD dosimeters to known doses of 1, 2, 3, and 4 mGy. The radiation was scattered off a Polymethylmethacrylate (PMMA) phantom at the position of the patient and measured at the approximate position of the primary operator. Two dosimeters were left unexposed in order to compensate for background signal. The calibration curve showed excellent agreement to linear regresson (R² = 0.999).

The Harshaw TLD-100H two-element dosimeters were analyzed by the Norwegian Radiation Protection Authority (NRPA) and the Harshaw DXT-RAD TLD-100 dosimeters were analyzed at Sahlgrenska University Hospital (Sweden).

The regional ethics committee found that the study did not need approval as both study groups would be treated according to common clinical practice.

Statistical analysis of the data was done using median with 95% confidence intervals with a Mann-Whitney test for difference between groups. Frequency data were compared using ratios and Fisher exact test for difference in groups. The significance level was set to 5% (P < 0.05).

Results

Table 2 shows the results from the dose measurements to the operator. As expected, the dosimeters placed at unshielded locations at the subject were exposed to more radiation than dosimeters placed in shielded locations. The unshielded dosimeters received an approximate dose reduction of 50% from phase one to phase two. Dosimeters placed inside the lead apron at chest and axillary level and outside the apron at knee level all had very low readings <0.1 mGy during both phases.

Table 2
Results of the TLD collective dose measurements on the operator. Dose reduction between phase one and two

Phase one Phase two

Position Dosimeter Dose (mGy) Dose (mGy) Dose reduction

Outside lead apron TLD-100H (H0.070 0.46 0.23 49%

Outside lead apron TLD-100H (H10) 0.39 0.20 47%

Hand (Dxt) DXT-RAD TLD-100 0.59 0.20 66%

Hand (Sin) DXT-RAD TLD-100 1.81 0.74 59%

Thyroid DXT-RAD TLD-100 0.31 0.14 54%

*Dosimeters placed inside the lead apron at chest and axillar level and outside apron at knee level all had very low readings <0.1 mGy during both phases and was thus excluded from the table

Comparing phase one and two, there was no significant difference in exposure time for fluoro or record modes (Table 3). There was, however, a significant difference in operation time (P = 0.04), with medians increasing from 50 min to 60 min from phase one to two.

Table 3
Comparison of record and fluoro exposure time and DAP for phase one and two. Medians for each phase is compared using a Mann-Whitney test

Phase one Phase two

Procedures Parameter Median 95%CI Median 95%CI P value

All procedures Fluoro time (min) 7.55^I 4.53–10.02 7.62 5.85–9.40 0.36

Phase one (n = 44) Fluoro DAP (cGycm²) 129.5 98–305 144 89–379 0.63

Record time (min) 0.52 ^III 0.38–0.75 0.75^IV 0.6–1.03 0.11

Phase two (n = 41) Record DAP (cGycm²) 222 137–493 265 182–564 0.21

Operation time (min) 50 40–55 60 45–65 0.04

Pelvis Fluoro time (min) 4.93^I 3.67–11.30 7.60 4.93–11.35 0.39

Phase one (n = 21) Fluoro DAP (cGycm²) 320 104–824 609 144–915 0.58

Record time (min) 0.45^I 0.32–0.75 0.38^II 0.27–0.70 0.77

Phase two (n = 21) Record DAP (cGycm²) 757 408–1274 654 509–1355 0.78

Operation time (min) 45 30–60 55 45–65 0.27

Lower extremities Fluoro time (min) 7.82 4.07–10.95 7.68 4.75–14.82 0.71

Phase one (n = 23) Fluoro DAP (cGycm²) 86 52–156 67 46–100 0.80

Record time (min) 0.67^II 0.43–1.00 1.02^II 0.77–1.38 0.02

Phase two (n = 19) Record DAP (cGycm²) 101 53–164 129 110–182 0.04

Operation time (min) 50 40–60 60 40–75 0.09

^I–IV = one to four missing data entries, respectively

For pelvic procedures, there was no significant difference in either fluoro or record exposure time or DAP between phase one and two (Table 3). Nor was there any significant difference in operation time (P = 0.27), however, the median operation time was 45 min and 55 min in phase one and two, respectively.

For lower extremity procedures, there was no significant difference in fluoro time and DAP between phase one and two, however, there was a significant difference in record time (P = 0.02) and record DAP (P = 0.04). The median record time increased from 0.67 to 1.02 min between phase one and two, respectively, and the median record DAP increased from 101 to 129 cGycm² in a corresponding manner. The operation time was not found significantly different (P = 0.09), the medians for phase one and two were, however, 50 and 60 min, respectively.

As shown in Table 3, both fluoro and record DAP for pelvic procedures were substantially higher than for lower extremitiy procedures (P < 0.01).

Discussion

Our results show an approximate 50% dose reduction to the operator during arterial interventional procedures when the operator systematically employs an automatic power injector and step back or leave the operating suite during DSA (Table 2). We find that this implies a great potential for dose reduction to the operator. However, this decrease of operator exposure seems to come at a cost of a small, but significant increase in procedure time (Table 3).

When stratifying the data by the anatomic region of the procedure, one can observe a significant increase in both record time and DAP for lower extremities, indicating an increase in patient dose for these procedures. This increase in patient dose was not observed in pelvic procedures.

When using the power injector during lower extremity procedures, an estimation of exposure delay in seconds must be given to the staff, to start the exposure as the contrast medium reach the area of interest. The operator may have shortened this delay during phase two, not being used to this technique. The length of the run may also be shorter during hand injection, as the operator controlled both contrast media and exposure, and was able to react directly to the acquired image to terminate the run. No delay was necessary during DSA in the pelvic area.

Previous studies show how the patient DAP correlate linearly with operator exposure through a scatter factor (1, 12). Hence the potential of dose reduction for different procedures can be estimated considering the record DAP. In our study the median DAP values for lower extremity and pelvic procedures, pooled for both phases were 125 mGycm² and 736 mGycm², respectively, reflecting the difference in body volume of the radiated area. This means the dose reduction potential in pelvic procedures is greater by a factor of five to six compared to lower extremity procedures.

Operator exposure increases with diameter of the radiated area (12), thus the operator is likely to benefit more from using a power injector and stepping back from a pelvic procedure in a patient with a high BMI compared to a patient with a low BMI. The exposure at waist level of the operator is shown to increase by 50% when the patient's abdomen diameter increases from 24 to 29 cm (12).

In our practice the operator can obtain the majority of the exposure reduction by employing the power injector during pelvic procedures only, thereby not increasing the patient dose during the lower extremity procedures.

The ratio between fluoro and record mode during the interventional procedure will also determine the potential for dose reduction to the operator. In neuroradiology where DSA is a larger part of the imaging, the possible dose reduction to the operator has been shown to be even larger than in our study; more than 75% (15).

When interpreting the results of this study one should keep in mind the limited number of patient procedures performed, especially when the data are stratified by anatomic region. However, the use of non-parametric statistics makes the analysis less sensitive to extreme values. In addition our study was conducted in a clinical interventional practice. Thus the patient population varies both in accordance to severity of disease and complexity in procedures, as well as in patient characteristics. However, there was no significant difference in the study population between phases one and two (Table 1).

The dosimeters placed inside the protection apron had very low readings, and the data from these are likely to consist of a noise dominated signal. We know from previous studies that only approximately 4% of the radiation crosses the protective apron at chest level, thus reducing dose below the detection limit for routine measurements by the Norwegian radiation protection authority (NRPA) of 0.1 mSv (19).

When micro catheters are in use, the injection of contrast media could not be done by power injector, due to the risk of small vessel and catheter rupture (16). For the patients procedures selected for this study, this limitation applied to procedures in the vessels of the calf and foot. Nevertheless, most DSA series are recorded through diagnostic or guiding catheters or through the introducer, as shown by the high number of automatic contrast injections conducted during phase two.

The development of interventional radiology point towards longer, more complicated procedures performed by experienced physicians, who dedicate their professional life to this type of work. Hence, while working within the national regulation limits of occupational radiation exposure; it is still important to minimize the occupational risk from operator exposure through an accumulated dose over an entire career. Every single measure that can contribute to reducing radiation exposure, without compromising patient safety during procedures should be employed. By using a power injector to deliver contrast media, the primary operator can use the opportunity to step back from the patient, in order to achieve a substantial reduction in exposure. This is easily combined with other measures such as good technique and protective shields.

In conclusion, this study has shown a dose reduction of approximately 50% to the operator using a power injector to deliver contrast media and thus allow the operator to step back from the patient in a clinical setting with pelvis and lower extremity procedures.

Conflict of interest: None.

	Phase one	Phase two
Sex (Male/Female)	18/26			23/18			0.12*
Anatomic area of procedure (Low. ex./Pelvis)	23/21			19/21			0.41*
Age (years)		73.5	63.0–78.0		70.0	64.0–75.0	0.91^†
Height (cm)		168	165–174		171	169–174	0.35^†
Weight (kg)		73.5	64.0–81.0		76.5	69.0–80.0	0.54^†
BMI (kg/m²)		24.0	22.2–25.9		25.1	24.2–27.4	0.17^†
Injections (n)		5	3–6		4	3–6	0.94^†

		Phase one	Phase two
Outside lead apron	TLD-100H (H0.070	0.46	0.23	49%
Outside lead apron	TLD-100H (H10)	0.39	0.20	47%
Hand (Dxt)	DXT-RAD TLD-100	0.59	0.20	66%
Hand (Sin)	DXT-RAD TLD-100	1.81	0.74	59%
Thyroid	DXT-RAD TLD-100	0.31	0.14	54%

		Phase one	Phase two
All procedures	Fluoro time (min)	7.55^I	4.53–10.02	7.62	5.85–9.40	0.36
Phase one (n = 44)	Fluoro DAP (cGycm²)	129.5	98–305	144	89–379	0.63
	Record time (min)	0.52 ^III	0.38–0.75	0.75^IV	0.6–1.03	0.11
Phase two (n = 41)	Record DAP (cGycm²)	222	137–493	265	182–564	0.21
	Operation time (min)	50	40–55	60	45–65	0.04
Pelvis	Fluoro time (min)	4.93^I	3.67–11.30	7.60	4.93–11.35	0.39
Phase one (n = 21)	Fluoro DAP (cGycm²)	320	104–824	609	144–915	0.58
	Record time (min)	0.45^I	0.32–0.75	0.38^II	0.27–0.70	0.77
Phase two (n = 21)	Record DAP (cGycm²)	757	408–1274	654	509–1355	0.78
	Operation time (min)	45	30–60	55	45–65	0.27
Lower extremities	Fluoro time (min)	7.82	4.07–10.95	7.68	4.75–14.82	0.71
Phase one (n = 23)	Fluoro DAP (cGycm²)	86	52–156	67	46–100	0.80
	Record time (min)	0.67^II	0.43–1.00	1.02^II	0.77–1.38	0.02
Phase two (n = 19)	Record DAP (cGycm²)	101	53–164	129	110–182	0.04
	Operation time (min)	50	40–60	60	40–75	0.09

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	Phase one			Phase two
	Ratio	Median	95% CI	Ratio	Median	95% CI	P value
Sex (Male/Female)	18/26			23/18			0.12*
Anatomic area of procedure (Low. ex./Pelvis)	23/21			19/21			0.41*
Age (years)		73.5	63.0–78.0		70.0	64.0–75.0	0.91^†
Height (cm)		168	165–174		171	169–174	0.35^†
Weight (kg)		73.5	64.0–81.0		76.5	69.0–80.0	0.54^†
BMI (kg/m²)		24.0	22.2–25.9		25.1	24.2–27.4	0.17^†
Injections (n)		5	3–6		4	3–6	0.94^†

		Phase one	Phase two
Position*	Dosimeter	Dose (mGy)	Dose (mGy)	Dose reduction
Outside lead apron	TLD-100H (H0.070	0.46	0.23	49%
Outside lead apron	TLD-100H (H10)	0.39	0.20	47%
Hand (Dxt)	DXT-RAD TLD-100	0.59	0.20	66%
Hand (Sin)	DXT-RAD TLD-100	1.81	0.74	59%
Thyroid	DXT-RAD TLD-100	0.31	0.14	54%

		Phase one		Phase two
Procedures	Parameter	Median	95%CI	Median	95%CI	P value
All procedures	Fluoro time (min)	7.55^I	4.53–10.02	7.62	5.85–9.40	0.36
Phase one (n = 44)	Fluoro DAP (cGycm²)	129.5	98–305	144	89–379	0.63
	Record time (min)	0.52 ^III	0.38–0.75	0.75^IV	0.6–1.03	0.11
Phase two (n = 41)	Record DAP (cGycm²)	222	137–493	265	182–564	0.21
	Operation time (min)	50	40–55	60	45–65	0.04
Pelvis	Fluoro time (min)	4.93^I	3.67–11.30	7.60	4.93–11.35	0.39
Phase one (n = 21)	Fluoro DAP (cGycm²)	320	104–824	609	144–915	0.58
	Record time (min)	0.45^I	0.32–0.75	0.38^II	0.27–0.70	0.77
Phase two (n = 21)	Record DAP (cGycm²)	757	408–1274	654	509–1355	0.78
	Operation time (min)	45	30–60	55	45–65	0.27
Lower extremities	Fluoro time (min)	7.82	4.07–10.95	7.68	4.75–14.82	0.71
Phase one (n = 23)	Fluoro DAP (cGycm²)	86	52–156	67	46–100	0.80
	Record time (min)	0.67^II	0.43–1.00	1.02^II	0.77–1.38	0.02
Phase two (n = 19)	Record DAP (cGycm²)	101	53–164	129	110–182	0.04
	Operation time (min)	50	40–60	60	40–75	0.09