Radiation Exposure During Endourologic Procedures Using Over-the-Table Fluoroscopy Sources

Abstract

Background and Purpose:

Fluoroscopy is used daily by endourologic surgeons worldwide without knowledge of received radiation doses. We wanted to assess the radiation exposure of endourologic surgeons by frequently performed endourologic interventions with an over-the-table x-ray system.

Patients and Methods:

In this prospective single-center study, 235 endourologic interventions in 188 patients from April to September 2010 were included. Sixty-seven ureteral stent placements (USP), 51 ureteral stent changes (USC), 67 percutaneous stent changes (PSC), 11 percutaneous nephrolithotomies (PCNL), and 39 ureterorenoscopies (URS) were performed by 12 surgeons. The surgeon`s radiation exposure was measured with one thermoluminescent dosimeter (TLD) at the forehead and one at the ring finger. TLDs were analyzed at a central institute. The radiation dose detected at the forehead was counted as representative for the lens of the eye and the thyroid.

Results:

Mean patient age was 60.6 (±18.8) years. Analysis of the TLD showed the following average values at the forehead for each intervention: USP and USC 0.04 mSv; PSC 0.03 mSv; PCNL 0.18 mSv; URS 0.1 mSv. Average finger values are: USP 0.13 mSv; USC 0.21 mSv; PSC 0.20 mSv; PCNL 4.36 mSv; URS 0.15 mSv.

Conclusions:

This report evaluates surgeons' radiation exposure by everyday endourologic interventions of different complexity. Most can be performed with an over-the-table x-ray system without exceeding statutory limits. Especially for PCNL, surgeons should consider possible protective action.

Introduction

I ncidence and prevalence of kidney stones are globally increasing while being independent from sex, race, and age.^1

–4 There are regional differences for both incidence and prevalence of urolithiasis. They range between 0.09 % and 1.47 % and 3.5 % and 18 %, respectively. Thus, the need for endourologic interventions increases similarly. Fluoroscopy is today a very important and widespread tool for endourologists and is used worldwide for many endourologic diagnostic and therapeutic procedures.

The use of fluoroscopic imaging results in radiation exposure to the endourologic surgeon, however. Tubes of the fluoroscopy units are positioned either over the couch or under the couch, the first ones being well known to deliver higher radiation doses to the surgeon than under-the-table systems.⁵ Nevertheless, most of the stationary fluoroscopic units in urologic departments are over-the-table systems because of better handling during procedures that require the surgeon at close range.⁶

The International Commission on Radiation recommends not to exceed the occupational limit of 20 mSv per year over a defined period of 5 years on average.⁷ Dose limit for the lens of the eye is 150 mSv; the recommended limit for the skin and extremities is 500 mSv.⁷ Beside these dose limits, the German Radiation Protection Ordinance in 2001 limits the effective organ dose to the thyroid to 300 mSv per year.⁸ Exceeding recommended dose limits for the extremities was found for cardiologists while performing difficult percutaneous procedures.⁹ Concerning the radiation exposure of endourologic surgeons, few studies have been done with only a small number of assessed interventions.^10,11 Furthermore, the wide range of measured or even calculated exposure doses that were described show a wide range. Most publications are focused on percutaneous nephrolithotomy (PCNL) and ureterorenoscopy (URS). Data concerning other regularly performed interventions remain elusive.

The aim of the present study was to evaluate whether endourologic surgeons are at relevant risk for significant radiation exposure. Furthermore, we assessed the differences in radiation exposure of specific interventions and dissected how many of these procedures could be performed without exceeding dose limits. To objectify the radiation exposure of endourologic surgeons through regularly performed interventions and to recognize risk factors that could be eliminated, we carried out this prospective study in an endourologic high-volume center.

Patients and Methods

From April to September 2010, 235 endourologic interventions were enclosed in this prospective single-center study. We chose PCNL, ureteral stent placement (USP), ureteral stent change (USC), URS, and percutaneous stent change (PSC) as the five most performed endourologic interventions with fluoroscopic support in our department. To measure the radiation dose to the urologist for each of these groups, two LiF:Mg,Ti thermoluminescent dosimeter rings (TLD 60, TLD POLAND, Krakow, Poland) were provided.

One dosimeter was fixed at the forehead of the surgeon by a headband to measure the radiation dose representative for the lens of the eye and the thyroid. The second ring was worn at the ring finger of the hand that was closer to the radiation field by steadying the instrument, depending on the surgeons' handedness.¹² The surgeons wore chest-, pelvic-, and thyroid radiation protection as well as lead-impregnated goggles.

All interventions were performed with two fluoroscopy units: Uroscope 3D (Siemens AG, Munich, Germany) with over-the-table tubes (Optitop 150/40/807HC 100, Siemens AG, Munich, Germany). Both fluoroscopy units use an over-the-table x-ray tube and an under-the-table image intensifier. The fluoroscopy units have a combined energy/current (kVp/mAmp) selector, which controls the radiation output at the tube and an automatic brightness control mode, which selects the optimal tube voltage and current automatically. Both fluoroscopy units do not have the technical opportunity to use pulsed fluoroscopy. The surgeon was in control of the foot pedal to activate the fluoroscopy unit. Movements of the table were performed by assisting staff according to the surgeons' instructions.

Included was every patient who underwent one of the defined interventions without combinations of them. As tract formation lead to the highest radiation exposure during PCNL, patients with previous nephrostomy tracts were excluded from the study. The thermoluminescent dosimeters (TLDs) were analyzed every 3 months with a TLD-Reader Harshaw H5500 (Thermo Electron, Solon, Ohio) at a central institute (Helmholtz Centre, Munich, Germany), which is an accredited institution with ISO 17025 certification. The average effective dose for the organs was calculated by dividing the detected effective dose in mSv by the number of performed cases. For USP, USC, and PSC, surgeons were separated in two groups depending on their experience: Group 1 with a level of endourologic experience less than 2 years and group 2 with more than 2 years of endourologic experience. All assessed data were documented in the surgical report by the surgeon immediately after the procedure.

The study was approved by the local ethics committee (No. 2011-212Str.-MA). All statistical calculations were performed with the SAS software, release 9.2 (SAS Institute Inc., Cary, NC). To compare two groups regarding a quantitative variable (ie, fluoroscopy time, operative time), Mann-Whitney U tests were used.

Results

There were 235 interventions performed in 115 males and 73 females with a median age of 60.6±18.8 years. Results of fluoroscopy time, operative time, total detected effective radiation dose (ERD), and calculated average ERD are shown in Table 1. By analysis of the TLD, the following average values at the forehead for each intervention were calculated: USP and USC 0.04 mSv; PSC 0.03 mSv; PCNL 0.18 mS; and URS 0.1 mSv, respectively. Average finger values are: USP 0.13 mSv; USC 0.21 mSv; PSC 0.20 mSv; PCNL 4.36 mSv; and URS 0.15 mSv. For USP (P<0.01) and PSC (P<0.01), the surgeon's experience showed significant influence on fluoroscopy time. For USP, there was also significant influence on operative time (P=0.03). For USC, a trend was found on operative time (P=0.09). Neither was there significant influence on operative time in PSC nor on fluoroscopy time in USC.

Table 1.

Overview of Collected Data for the Different Interventions with Calculated Average of the Effective Radiation Dose

		Fluoroscopy time (min)	Operative time (min)	Total ERD (mSv)		Average ERD/procedure (mSv)
Procedure	n	Med [range]	Med [range]	Forehead	Finger	Forehead	Finger
Ureteral stent placement	67	1 [<0.1–7.2]	22 [7–80]	3	9	0.04	0.13
Ureteral stent change	51	0.7 [<0.1–5.75]	16.5 [5–46]	3	11	0.06	0.22
PSC	67	0.6 [<0.1–3.6]	10 [3–30]	2	14	0.03	0.22
PCNL	11	7.3 [5.3–15.7]	110 [40–161]	2	48	0.18	4.36
URS	39	1.1 [0.2–13.9]	46 [14.5–219]	4	6	0.10	0.15

ERD=effective radiation dose; PSC=percutaneous stent change; PCNL=percutaneous nephrolithotomy; URS=ureterorenoscopy; min=minutes; mSv=millisievert; med=median.

Table 2 shows the detected radiation exposure in our study compared with previous published data by other authors. Table 3 points out the possible interventions without exceeding statutory dose limits in our study.

Table 2.

Radiation Exposure to the Surgeon by Different Endourologic Procedures

Author (Year)	n	Procedure	Dosimeter position	Dose/case [± SD]	Dose unit	Dose in mSv	Mean fluoroscopy time (min)
Ritter 2011^a	11	PCNL	Finger	4.36	mSv	4.36	7.3
			Head	0.18		0.18
	39	URS	Finger	0.15		0.15	1.1
			Head	0.1		0.1
Lowe 1986^{12 b}	7	PCNL	Neck	2.5 [± 3.4]	mrad	2.5	27.8
			Right hand	2.2 [± 2.3]		2.2
			Left hand	9.4 [± 21.2]		9.4
			Finger	0.21		0.21
Rao 1987^{13 b}	18	PCNL	Finger	7.5	mSv	7.5	21.9
			Hand	5.2		5.2
			Eye	1.6		1.6
Giblin 1996^{14 a}	5	URS	Chest	11	mSv/hour	NA	NA
Hellawell 2005^{15 b}	18	Ureteral procedures	Head	1.9 [± 0.5]	μGy	0.0019	1.3
			Eye	2.7 [± 0.7]		0.0027
			Lower leg	11.6 [± 1.6]		0.0116
			Foot	6.4 [± 1.6]		0.0064
	6	PCNL	Head	40 [± 10]	μGy	0.04	10.7
			Eye	48 [± 12]		0.048
			Lower leg	167 [± 42]		0.167
			Foot	93 [± 23]		0.093
Kumari 2006^{16 b}	50	PCNL	Finger	0.36 [± 0.13]	mSv	0.36	6.04
			Trunk	0.056		0.056
Majidpour 2010^{17 b}	100	PCNL	Head	0.47	μGy	0.00047	4.5
			Eye	0.04		0.00004
			Finger	0.21		0.00021
			Leg	4.1		0.0041

Overcouch system.

Undercouch system.

mSv=millisievert; min=minutes; PCNL=percutaneous nephrolithotomy; URS=ureterorenoscopy, mrad=millirad; μGy=microgray.

Table 3.

Possible Numbers of Procedures Per Year Until Recommended Dose Limits Reached in our Study

	Possible no./year until dose limit
Organ (dose limit/year)	Lens (150 mSv)	Finger (500 mSv)	Thyroid (300 mSv)
USP	3750	3846	7500
USC	2500	2272	5000
PSC	5000	2380	10000
PCNL	833	114	1666
URS	1500	3333	3000

mSv=millisievert; USP=ureteral stent placement; USC=ureteral stent change; PSC=percutaneous stent change; PCNL=percutaneous nephrolithotomy; URS=ureterorenoscopy.

Discussion

Despite comprehensive research, exact data about the health effect of low-level radiation is lacking.^13,14 As long as we do not know for sure if even low exposure to ionizing radiation increases our risk of cancer development or if it even protects us,¹³ all possible protective action should be taken. The following issues must be addressed: Wearing appropriate 0.5 mm lead shielding, minimizing the use of fluoroscopy, staying away from the radiation beam as far as possible, not exposing unprotected areas of the body to the beam, and using under-the-table fluoroscopy units, if possible.

Pulsed fluoroscopy is another very important feature that is available with the latest generation of fluoroscopic units. It reduces radiation exposure of the surgeon up to 60%. While many of the older over-the-table systems in use still do not have pulsed fluoroscopy,⁶ the surgeon's attention should turn to the other mentioned protective measures. Minimizing the use of fluoroscopy means following the ALARA principle (as low as reasonably achievable) that is a basic part of statutory fixed radiation protection.⁵

In former studies, dosimeters were worn on both hands during the interventions.^12,15 Results from monitors worn on different fingers of both hands show a consistent variation between the fingers, with the index finger of the left hand receiving the highest dose. This was shown to be consistent for a right-handed surgeon using his left hand to steady instruments during fluoroscopy.¹² Therefore, measurements at the ring finger were performed at the hand that was closer to the radiation beam, depending on the handedness of the surgeon.

A study by Hellawell and coworkers¹⁵ found the feet or lower legs to be the most exposed parts of the body for under-the-table tube positions. Because we work with an over-the-table system, we decided to focus on the sterically closest parts of the surgeon's body, which are the index finger of the hand used to steady the instruments and the forehead, representing the lens of the eye and the thyroid. It is evident that over-the-table tube positions cause higher exposure to the eyes and the thyroid. Therefore, regular surveillance was recommended by earlier authors.¹⁶ The use of lead curtains can reduce scatter radiation by a factor of 30 to 70. They are common in under-the-table systems, but in over-the-table tube position, they are impractical for endourologic interventions, which require sterile conditions.¹⁶

Tanriverdi and associates¹⁷ found a mean fluoroscopic screening time for an excellent endourologic surgeon performing PCNL of 7.02 (±3.5) minutes. The 7.3 [5.3–15.7] minute fluoroscopy time during PCNL in our study is similar to earlier reported data. Kumari and colleagues¹⁸ and Majidpour¹⁹ mentioned 6.04 minutes and 4.5 minutes, respectively. This is in contrast to data reported by Hellawell and coworkers¹⁵ who found 10.7 minutes. This study, however, was limited because of a low number of patients (n=6). The authors mentioned doses for 18 ureteral procedures that were detected with six different interventions with a wide range of fluoroscopy time, which is the reason the data are not well comparable.

In our study, the detected radiation exposure during PCNL, especially to the surgeon's finger, was considerably increased compared with recently published data.^15,8,19 Former studies in the 1980s found even higher radiation doses either to the legs or the fingers going along with fluoroscopic screening times three- to four-fold higher than ours.²⁰ In our study, the higher finger doses that we detected can ultimately be ascribed to the use of the over-the-table tube position that requires the surgeon to work in the radiation beam directly.

Nevertheless, even with this technical constraint, a surgeon can perform 114 PCNLs without exceeding the statutory dose limit of 500 mSv to the extremities. Furthermore, the radiation dose is far away from risking deterministic radiation effects such as erythema of the skin that might occur above an effective skin dose of 2.5 Gy. Because of the much lower radiation exposure of the surgeon by less complex procedures such as URS, USP, USC or PSC, these can be performed using common protective gear without endangering the surgeon until a huge amount of procedures are performed (Table 3).

The significant differences between the two groups for PSC seem to be related to a greater gap in experience, when completely inexperienced colleagues perform their first steps in endourology. The fact that we did not find significant differences in the more complex procedure, USC, might be because of some experience of group 1 until these surgeons perform this procedure and therefore narrow this gap.

Limitations of our study are caused by the variety of difficulty in operation procedures, especially in endourologic interventions. An average calculation of radiation exposure does not take into account variations from stone burden, stone location, or patient body mass index. Lowe and colleagues¹² noted that significantly higher levels of radiation exposure can occur during long-lasting and difficult procedures. Thus, the potential for higher levels of radiation exposure clearly exists, and proper precautions need to be followed at all times. These differences in difficulty lead to a wide range of data in operative time and fluoroscopy time. Therefore a sufficient amount of procedures needed to be investigated to allow statistical analysis of the detected values.

Separate dosimeters for each single procedure would be necessary to reduce this inaccuracy. The dosimeters themselves, however, cause inaccuracy, because the error in the TLD reading is up to 30%.²¹ Meanwhile, a median value of the surgeon's exposure dose gives an idea of how close high-volume surgeons might reach recommended dose limits.

Another limitation of our study consists in the fact that only two specific parts of the body are represented by the dosimeters, and both dosimeters are in different positions because of different surgeons' constitutions. On the other hand, this fact enables a good average determination of radiation dose exposure, because surgeons are not in a steady state during the procedure. Skin doses are a poor index of true risk, because the doses to deeper tissues may vary widely for the same skin dose depending on tissue depth, radiation energy, beam angulation, and other factors. Because deeper tissues receive less radiation than the skin, the skin dose represents the upper limit of radiation exposure for the tissues at risk. Although not perfect, skin doses are the most uniform and best available for comparison of different interventions.¹²

Conclusion

Fluoroscopy units with over-the-table x-ray tubes are widespread because of comfortable handling in endourologic interventions. By using these systems, the thyroid, the lens of the eye, and the surgeon's finger are more exposed to radiation during endourologic interventions than with under-the-table tube positions. In our study, however, even high-volume endourologic surgeons would not reach the statutory dose limits unless they perform more than 114 PCNLs per year. Endourologic surgeons, who mainly perform URSs or other transurethral interventions, are within safe radiation limits even with a large amount of interventions per year. Experience of the endourologic surgeons can lead to a significant reduction of fluoroscopy time in some endourologic procedures.

Footnotes

Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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