Radiation exposure of patient and surgeon in minimally invasive kidney stone surgery

25 mai 2016

Auteurs : A. Demirci, O. Raif Karabacak, F. Yalç?nkaya, O. Yi?itba??, C. Akta?
Référence : Prog Urol, 2016, 6, 26, 353-359



Percutaneous nephrolithotomy (PNL) and retrograde intrarenal surgery (RIRS) are the standard treatments used in the endoscopic treatment of kidney stones depending on the location and the size of the stone [1]. Fluoroscopy is used in the diagnosis and the treatment procedures in urolithiasis surgeries which causes the radiation exposure of the patient and the surgeon [1, 2].

The most important factor in the determination of the radiation exposure during the procedure is the fluoroscopy time. The type of the procedure, experience of the surgeon, patient anatomy, and the quality of shots are among the factors affecting this time [3]. It is important to follow the operation rules to keep the radiation dose ‘As low as reasonably achievable (ALARA)', the principle developed by Cabrera et al., to keep the fluoroscopy time as short as possible, and to use the appropriate radiation protection and dosimetry [4].

In this study, we aim to contribute to our knowledge about the measurement of radiation exposure of the patients and surgeons during the PNL and RIRS, and determining the appropriate fluoroscopy time and the approach for the operation, and the conscious application of the approach. Also, we aimed to show the radiation exposure difference between the minimally invasive techniques used in stone surgery by synchronously measuring the radiation exposure of the patients and the surgeons in each session.

Materials and methods

Our study is a prospective study. It included 20 patients who underwent PNL, and 45 patients who underwent RIRS in our clinic between June 2014 and October 2014.

Age, gender, stone location, stone size of the patients, and the fluoroscopy time and radiation exposure of the patient and the surgeon were recorded. The patients were assessed in the postoperative third month of the operation for residual fragments using renal ultrasound. The surgeries were performed by multiple surgeons with at least ten years of experience in stone surgery.

The patients, who had stones smaller than 2cm, first underwent SWL for<2cm stones. The patients who had unsuccessful SWL history or who were not suitable for SWL were included in the study. The radiation exposure during SWL was not measured. Patients with renal abnormalities or skeletal deformities were excluded from the study. It was left to the operating surgeon to decide about the group the patients are placed in.

Operations were divided into three steps; step 1: the access sheath or urethral catheter placement, step 2: lithotripsy and collection of fragments, and step 3: DJ catheter or re-entry tube insertion.

We used bull's eye technique for the access in PNL. To the patients undergoing RIRS, DJ catheter was placed for the postoperative residual fragments.

Radiation exposure measurements were determined, for the patients, by placing thermoluminescent dosimeter (TLD) between the operation table and the patient at the location of the kidney, and for the surgeons, by placing TLD under the protective jacket of the operating surgeon. ZHÄ°EMâ„¢ C-arm fluoroscopy unit was used during the procedure. Collimation was used to decrease the radiation dose.

‘ALARA' principle was applied during the operation. Dosimeters were evaluated monthly at the Turkey Atomic Energy Agency Sarayköy Nuclear Research and Training Center.

Radiation exposure management

Preoperative patient assessment

The radiation exposure history and the pregnancy status of the patients were questioned.

Intraoperative patient assessment

Fluoroscopy time is the single most important determinant of the radiation exposure of the patients. Thus we recorded the fluoroscopy time, and used the last image hold to help shorten the exposure time.

The operators had optimal work habits, the knowledge of radiation physics, familiarity with tableside controls of the x-ray equipment, and a commitment to radiation safety.

In the study, lead collimators were used to restrict the cross-sectional area of the beam exiting the x-ray tube.

The patients were positioned as far from the x-ray tube and as close to the image intensifier as possible for optimal image quality and minimal radiation dose.

Postoperative patient assessment

Radiation dose was measured during the surgery, and included in the patient's medical record.

Management of occupational exposure

Shielding, distance to the radiation source, and dosimetry are the most important protective factors. Thus, the surgeon and the operating room staff were required to participate in a facility-based radiation dosimetry monitoring program, and used lead equivalent aprons, thyroid shields, and leaded goggles for protection.

Statistical analysis

Data analysis was performed using SPSS for Windows 11.5 software. Kolmogorov-Smirnov test was used to investigate whether the distribution of the continuous and discrete numerical variables was consistent with the normal distribution.

Significance of the difference in the mean values between the groups was assessed by Student's t test. Significance of the difference between the groups in terms of median values was analyzed using the Mann-Whitney U test when the number of independent groups was two, and the Kruskal-Wallis test was used in the analysis when the number of groups was more than two. In the cases that the Kruskal-Wallis test statistical results were significant, Conover's non-parametric multiple comparison test was used to determine the condition(s) causing the difference.

Spearman correlation test was used to investigate whether there was a statistically significant relationship between the continuous numeric variables. Categorical variables were assessed using Pearson's Chi-square or Likelihood Ratio test. In each group, the significance of the difference between the steps in terms of the processing time and the amount of the radiation was examined by Wilcoxon sign test.

Unless otherwise specified, P value of<0.05 was considered statistically significant. However, the Bonferroni-correction was applied to control for type I error in all possible multiple comparisons.


Of the 20 patients who underwent PNL, 11 were males (55%), 9 were females (45%); of the 45 patients who underwent RIRS, 30 were males (66.7%) and 15 were females (33.3%). The mean age of the patients were 48.6±12.3 years, and 41.2±11.3 years; mean stone sizes were 30mm (16-60), and 12mm (7-35); mean fluoroscopy times were 337s (200-679), and 37s (7-351); and the total radiation exposures were 142 mBq (44.7 to 221), and 4.4 mBq (0.2 to 30) for the PNL and RIRS groups, respectively (Table 1).

In the third month of postoperative period, fragments in the ultrasound which were<5mm were assessed as clinically insignificant, and it was seen that none of the patients needed another surgery.

The radiation exposure of the surgeons for each case was lower than 0.1 mSv, and there was no significant difference between PNL and RIRS groups.

It was seen that, at each step, fluoroscopy times and radiation exposures according to the groups were significantly higher in the PNL group compared to the RIRS group; there was no radiation exposure or time difference in terms of localization when assessed in itself; the time and radiation exposure were stable in RIRS, and radiation exposure was the highest in step 1, and the lowest in step 3 in PNL (Table 2, Table 3).

For the 19 PNL patients and the 12 RIRS patients whose stone sizes were≥2cm, the fluoroscopy time in step 1, and the radiation exposure in steps 1 and 2 were found to be higher in the PNL group, and the results were statistically significant (P <0.001).

In terms of the stone sizes, in PNL groups, radiation exposure increased with the increase in the stone size in step 1; and in RIRS, the fluoroscopy time increased in step 2 (Table 4).


In the treatment of urolithiasis, minimally invasive techniques such as PNL, RIRS and SWL are used more frequently than the open surgery. During the surgical interventions, the patient and the surgeon are exposed to fluoroscopy which causes a risk due to cumulative radiation exposure.

A great number of studies show that the radiation exposure of patients is often underestimated by the physicians [5]. In fact, although X-ray collimation prevents the surgeon from direct radiation, the patient becomes secondary source by absorbing radiation during the procedure [6, 7]. For that, it is important to make effective use by considering that this increases the risk of malignancy.

‘The International Commission on Radiation Protection' emphasizes that the average annual effective dose limit should be 20mSv as the occupational exposure limit in 5-year duration. In addition, studies stated that the medical personnel are affected by the secondary reflected beams more, and that the dose for a surgeon who performs 50 PNL cases annually should not exceed 10mGy [7, 8].

There have been efforts to reduce the radiation dose received. Lipkin et al., in their study where they measured the radiation exposure of the patients, evaluated the organ-specific radiation exposure and found that it was the highest at the skin entrance in PNL, 0.24mGy/s, and 0.26mGy/s on the left and the right respectively [9]. Cabrera et al. emphasized, with the principle ‘As low as reasonably achievable (ALARA)' the importance of narrowing down the area exposed, using intermittent fluoroscopy, positioning the image intensifier input as close to the patient as practicable, trying to get magnified images, and saving the images and transferring them to other displays [4].

Kirac et al. suggested the reduced fluoroscopy protocol in RIRS patients, and showed that it could be used safely for urinary stone in patients without kidney abnormalities [10]. In this study, the aim was to reduce radiation by using the ALARA principle.

When we examine the studies that assessed the patients who underwent PNL, Kumari and Kumar applied PNL to 35 male and 15 female patients, and found the mean procedure time to be 75min (30-150min), mean fluoroscopy time to be 6.04min (1.8-12.16min), and the average radiation exposure of the patients to be 0.56 mSv (SD±0.35) [7]. Soufi and Majidpour determined the mean fluoroscopy time as 4.5min (1-8min) in 100 PNL patients [8].

Safak et al. showed that during PNL, in anterior-posterior and in 30 oblique positions, the mean entrance skin doses were 191 and 117mGy, respectively; and the effective dose per operation for the urologist was 12.7mSv [11]. Our study included 20 PNL patients; the mean fluoroscopy time was 5.61min; the mean radiation exposures of the patient and the surgeon were found 142mSv, and<0.1 mSv respectively, and it was seen that these results were close to the world average.

Tepeler et al., in a study where they examined the factors affecting the fluoroscopy times in PNL, found the mean fluoroscopy time of 282 cases managed by one surgeon to be 10.19±6.3min (range 3-50min); and the mean stone size to be 8.46±5.11cm2 (2-30); showed that the fluoroscopy time increased with the increase in the stone burden (P =0.001) and with the procedure of multiple access (P =0.007). They reported that the stone configuration and access location did not affect the fluoroscopy time [12]. In our study, the patients were applied one access, the operation was assessed in steps, which was different than the other studies, and radiation exposure was examined along with the fluoroscopy time. We found that the highest exposure occurred in step 1 until reaching the stone, and the lowest exposure occurred in step 3 when re-entry is placed which would not be affected by the localization of the stone. We also found that the radiation exposure in step 1 increased with the increase in stone size.

In the comparison of the groups, fluoroscopy time and radiation dose were significantly higher in the PNL patients. We found an increased radiation exposure during the access to the stone (92.5mSv, P <0.001). We have not come across any study on this in the literature, which makes our study unique.

Use of RIRS in the treatment of urolithiasis has been increasing in the last decade. It has been shown that recording and assessing the fluoroscopy times are important in order to decrease the radiation exposure in patients who undergo RIRS.

Lipkin et al. showed that the presence of a laser guide in the C-arm fluoroscopy unit, the use of glide wire tactile sensors, placement of the stent using cystoscope, working with the same fluoroscopist, and using single pulse mode shortened the time of exposure 86% (from 86.1s to 15.5s) [6]. Another study showed the importance of the experience of the urologist in uncomplicated unilateral ureteroscopies [13]. In this study, we recorded the times of the surgeries performed by the surgeons with at least 10 years of endo-urology experience.

Kirac et al. included in their study 76 patients with urolithiasis who underwent RIRS, with mean age 39.9±13.8years, and mean stone size 14.1±4.1mm. Access sheath was placed using single dose fluoroscopy, additional images were obtained to locate the stone (n =2). Fluoroscopy was applied to 4 patients who had undergone renal surgery before and had severe hydronephrosis, to determine the anatomy of the renal collecting duct system. The mean fluoroscopy time was found 5.27±1.8s [10].

Sfoungaristos et al. conducted a study where ureterorenoscopy was applied to 92 patients. They showed that there was a significant correlation between the fluoroscopy time and the stone size (P =0.009) [14]. Violette et al., in a prospective study with 76 patients who underwent ureterorenoscopy, measured the mean stone size as 10±5mm and the mean fluoroscopy time as 183s, and stated that the stone characteristics did not affect the fluoroscopy time [15]. In our study, the fluoroscopy time of the patients who underwent RIRS was measured as 37s and the radiation dose as 4.4 mSv. Our study differed from other studies in that it investigated at which step during the operation the highest exposure occurred, and found that with the increase in stone size, fluoroscopy time in step 2 increased but the localization did not affect the time and thus the exposure.

Number of studies comparing PNL and RIRS examined the parameters such as the rate of stonelessness, complication rates, postoperative decrease in hemoglobin value, and the length of hospitalization [16]. In literature, the number of studies comparing PNL and RIRS in terms of fluoroscopy time is insufficient. In a study that examined 233 patients who underwent upper urinary system stone procedure, ureterorenoscopy was applied to 127 patients, and PNL was applied to 106 patients, and median fluoroscopy exposure was found to be 43.3mGy for PNL, and 27.6mGy for ureterorenoscopy [17].

In our study, when the patients with the urinary stone size≥2cm who underwent PNL and RIRS were compared, fluoroscopy time and radiation exposure until reaching the stone in step 1 were found to be respectively 236s (133-324), 89.7mSv (67.9-165.4) (P <0.001); and 10s (2-57), 0.8mSv (0.2-11.3) (P <0.001), both of which increased statistically significantly. Although there is a need for further studies, we think that these results make a significant contribution to the preference of RIRS as it is more reliable than PNL.

Another part of our study that differed from other studies was that we assessed the effect of the stone localization on the results in stones with≥2cm size, and the operations in steps; it was seen that there was limited numbers of studies on this. In the PNCL and RIRS patients with stones≥2cm, the mean fluoroscopy times were 326s and 78s; radiation doses 130.3mSv and 8.3mSv respectively and it was determined that these values were greater than the mean values of the recent studies.


The small number of cases in the groups is the limitation of our study.


Due to the increasing use of fluoroscopy, it is important to raise awareness to reduce the radiation exposure. The selection of the surgical technique is as important as the protective measures.

Although there is need for more prospective randomized studies, RIRS appears to be more eligible than PNL because it has short fluoroscopy time, and the radiation exposure is low in all steps for the patients with kidney stones sizes≥2cm, and therefore it can be used safely.

Disclosure of interest

The authors declare that they have no competing interest.

Table 1 - Clinical findings of patients according to groups.
Variables  PNL (n =20)  RIRS (n =45)  P value 
Age (years)   48.6±12.3  41.2±11.3  0.021a 
Male  11 (55.0%)  30 (66.7%)  0.368b 
Female  9 (45.0%)  15 (33.3%)  0.368b 
Size (mm)   30 (16-60)  12 (7-35)  <0.001c 
Lower  7 (35.0%)  19 (42.2%)  0.583b 
Medium  4 (20.0%)  8 (17.8%)  >0.999d 
Pelvis  5 (25.0%)  13 (28.9%)  0,746b 
Upper  4 (20.0%)  5 (11.1%)  0,440d 
Total time (s)   337 (200-679)  37 (7-351)  <0.001c 
Total radiation dose (mSv)   142 (44.7-221)  4.4 (0.2-30)  <0.001c 

Student's t test.
Pearson's Chi-square test.
Mann-Whitney U test.
Fisher's exact test.

Table 2 - The fluoroscopy time in each step according to the groups and localization.
  PNL (s)  RIRS (s)  P valuea 
1st step        
Lower  236 (133-324)  10 (2-120)  <0.001 
Upper+medium  226 (140-340)  15 (4-55)  <0.001 
Pelvis  288 (160-487)  15 (2-47)  <0.001 
bP value  0.327  0.848   
2nd step        
Lower  76 (50-236)  13 (0-180)  0.003 
Upper+medium  78 (50-125)  7 (0-90)  <0.001 
Pelvis  65 (14-170)  11 (0-310)  0.014 
bP value  0.862  0.584   
3rd step        
Lower  14 (9-50)  6 (0-62)  0.041 
Upper+medium  11.5 (5-27)  4 (0-60)  0.268 
Pelvis  15 (12-60)  9 (0-31)  0.075 
bP value  0.421  0.855   

The comparisons between the PCNL and RIRS groups in each location, according to Bonferroni-corrected Mann-Whitney U test; the results were considered statistically significant for P <0.0056.
The comparisons between the localizations in PCNL and RIRS groups, according to Bonferroni-corrected Kruskal-Wallis test, the results were considered statistically significant for P <0.0083.

Table 3 - The radiation dose in each step according to the groups and localization.
  PNL (mSv)  RIRS (mSv)  P valuea 
1st step        
Lower  89.7 (67,9-165.4)  0.9 (0.2 to 11.3)  <0.001 
Upper+medium  80.3 (29,9-168.2)  1.6 (0.1 to 6.5)  <0.001 
Pelvis  118.1 (56,1-134.2)  1.4 (0.1 to 5.7)  <0.001 
bP value  0.666  0.648   
2nd step        
Lower  33.5 (25.5-59.6)  1.2 (0 to 26.3)  <0.001 
Upper+medium  28 (13.3-45.9)  0.7 (0 to 8.2)  <0.001 
Pelvis  16.7 (6.2-42)  1.0 (0 to 12.5)  <0.001 
bP value  0.102  0.806   
3rd step        
Lower  7.1 (4.6 to 17.2)  0.9 (0 to 6.5)  <0.001 
Upper+medium  3.8 (1.4 to 12.7)  0.7 (0 to 5.5)  0.013 
Pelvis  6.6 (2-26.4)  0.6 (0 to 3.6)  <0.001 
bP value  0.468  0.806   

The comparison between the PNL and RIRS groups in each location, according to Bonferroni-corrected Mann-Whitney U test; the results were considered statistically significant for P <0.0056.
The comparisons between the localizations in PCNL and RIRS groups, according to Bonferroni-corrected Kruskal-Wallis test; the results were considered statistically significant for P <0.0083.

Table 4 - Fluoroscopy time and radiation dose in each step according to groups localized in the lower pole≥2cm stones.
  PNL  RIRS  P valuea 
Fluoroscopy time (s)        
1st step  236 (133-324)  10 (2-57)  <0.001 
2nd step  76 (50-236)  60 (5-180)  0.383 
3rd step  14 (9-50)  8 (2-62)  0.383 
The radiation dose (mSv)        
1st step  89.7 (67.9-165.4)  0.8 (0.2-11.3)  <0.001 
2nd step  33.5 (25.5-59.6)  5.4 (0.9 to 26.3)  0.002 
3rd step  7.1 (4.6 to 17.2)  2.1 (0.1 to 6.5)  0.007 

According to Bonferroni-corrected Mann-Whitney U test, the results were considered statistically significant for P <0.0056.


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