Factors Influencing Fluoroscopy Use During Ureteroscopy at a Residency Training Program

Introduction

Ionizing radiation is used extensively throughout urologic surgery in the form of fluoroscopic guidance. ¹ Fluoroscopy (fluoro) is particularly critical for upper tract navigation during retrograde ureteroscopy (URS). ^1,2 Recently, there has been increased attention given to the hazards of radiation exposure on the patient, surgeon, and operating room (OR) staff during endourologic procedures. ¹ It is well known that there is a linear-no-threshold relationship between radiation exposure and carcinogenesis. ^{3 –6} Radiation exposure has been shown to increase the risk for skin, hematologic, and solid organ cancers. ^4,5 This is of high concern for patients with stone disease, requiring multiple endourologic procedures and frequent axial imaging, as well as for urologists and OR staff who have long-term occupational exposure. ^1,5,7,8

Radiation induces cellular death and damage in an energy-dependent manner. ⁴ Gray units (Gy) quantify the radiation required to deposit 1 Joule of energy per kilogram of target matter. Absorbed dose is the radiation absorbed by the target, and is calculated from air kerma (both measured in Gy). ^{3 –5,9} Air kerma and fluoroscopy time (FT) are two parameters provided by the fluoro machine. ⁹ Equivalent dose accounts for tissue-specific differences in absorption, is measured in Sieverts, and describes biological risk of radiation exposure. ^3,4 The effective dose (ED) is the sum of equivalent doses. ^3,5,9 The equivalent dose and ED, therefore, carry great clinical significance, as they can be used to determine risk from radiation exposure. ³

Intraoperative FT is directly associated with radiation dose to the patient and surgeon, ^10,11 which has prompted investigation into predictors for increased FT in URS. FT has been compared during URS when either the surgeon or a radiation technologist had control over the foot pedal. ^11,12 One study found that it is preferable for the surgeon to operate the foot pedal in standard URS cases, but not during laser lithotripsy. ¹¹ Another potential predictor for FT may be surgeon experience, as less experienced surgeons may rely on fluoro more heavily. A review of several studies analyzing the learning curve associated with urologic surgery found multiple measures differed significantly between novice and experienced surgeons. Intraoperative blood loss, complication rate, and operative time (OT) all decrease when the surgeon is more experienced, ¹³ and OT is a significant predictor for FT. ⁸

Growing concern over carcinogenic risk has led researchers to seek out techniques to decrease intraoperative radiation exposure. ¹⁰ Factors that affect radiation dose include distance from the radiation source, device settings such as X-ray tube voltage and current, and time exposed. ^14,15 One study found that radiation dose decreased when phantom dosimeters were placed further from the radiation source. ¹⁶ Positioning the patient closer to the image intensifier may, therefore, limit patient radiation dose. Decreasing radiation intensity settings reduces exposure during urologic surgery. In particular, this can be accomplished by using intermittent pulse rate or single-pulse-per-second. ^17,18 Some groups have even demonstrated effective fluoro-free URS ¹⁹ and ureteral stent placement. ²⁰

The effect of surgeon experience on intraoperative radiation use is an area that merits further study. ¹ There are few reports on the amount of radiation used by urology resident trainees performing URSs. One study found that a fellow in a 2-year endourology fellowship reduced FT during URSs by 50.7% by their second year. FT in their second year was comparable to FT used by an experienced endourologist. ²¹ A similar trend is observed when examining FT used by urology residents. FT used by two urology residents during URSs decreased as a function of case number over their first 2 years of training (postgraduate year 1 [PGY1]–postgraduate year 2 [PGY2]). ⁶ PGY2 residents used 17.5% less fluoro during URS than PGY1. PGY2 residents were also more likely to benefit from a radiation awareness program. ¹⁰

Currently, little data exist on the amount of radiation used during URSs by urology residents over the course of their training. We present the largest database evaluating fluoro use during URSs at a resident training program. Our primary objective was to assess FT at various experience levels, and to identify factors that may lead to increased FT during URSs. The expectation was that FT decreases incrementally as experience increases. Our secondary objective was to assess the effect of experience on OT.

Materials and Methods

A retrospective institutional review board exempt database was analyzed for this study. The OR records from two hospitals involved in a residency training program were queried for all surgeries that were documented as having URS performed between January 2015 and June 2019. In total, 444 surgeries were initially identified, of which 202 procedures were omitted as they were either not performed by core faculty, not coded properly, or there was no FT documented. We did not exclude surgeries wherein no stone was identified or for diagnoses other than urolithiasis. This resulted in 242 surgeries being performed by two attending physicians. One physician performed 70 surgeries whereas the other did 172 surgeries. The surgeon with 70 procedures has been in practice >20 years and has performed ∼1500 URSs. The surgeon with 172 procedures has been in practice for 9 years and has performed >500 URSs. Of the total 242 surgeries, 105 were performed solely by the attending physician. The other 137 procedures were performed by urology residents [63 for the first year (Uro1), 55 by the second year (Uro2), and 19 by the third year (Uro3)] with direct supervision from the attending urologist. The primary resident operating for each case was determined by analyzing operative dictations. At our institution, the resident performing the majority of the surgeries is responsible for the dictation.

A thorough chart review of the medical records was performed for all 242 surgeries. We reviewed outpatient office visits, operative reports, OR documentation, and preoperative imaging. Demographic data including gender, age, body mass index (BMI), and race were recorded. Surgery-specific data included OT, FT, presence of bilateral URS, use of flexible or rigid URS, use of an access sheath, ureteral dilation, presence of pre- and postoperative ureteral stents, stone size, stone location, and was URS effectively performed. Stone size was based on the operative dictation if no preoperative imaging could be identified. When residents performed the surgery, the year and total months of training were recorded. Use of a retrograde pyelogram was not recorded as it is the standard at this institution.

Fluoro is performed using a BV Pulsera or a Veradius Unity (Philips) mobile C-arm. Selection of the unit is made based on availability. A radiology technician manipulates the C-arm and gives static and live images at the command of the surgeon. Documentation of FT is performed by the radiology technician in the operative paperwork. Flexible URS is performed using the URF-P6 ureteroscope (Olympus). All wires and basket retrieval instruments are products of Boston Scientific. Specific choices of wires and baskets are made on a case-by-case basis and are not recorded. We use the VersaPulse PowerSuite 20W holmium laser (Lumenis) with either a 272 or 365 μm fiber.

Statistical analysis was performed using SPSS (IBM, Armonk, NY). Descriptive statistics were used to analyze patient demographics. Surgeries performed by attendings and residents of different experience levels were compared using analysis of variance (ANOVA) to determine differences in FT and OT. Bonferroni correction was used to identify specific differences. Spearman correlation coefficients were analyzed to detect correlations between all variables and FT. Multiple linear regression (MLR) was subsequently used to determine predictors of FT during URS.

Results

All demographic data are presented in Table 1. Table 2 presents the ANOVA results for OT and FT. A statistically significant relationship (p < 0.05) was observed for OT. Specifically, there was a statistically decreased (p < 0.05) OT when comparing Uro1 (45.9 minutes) with attendings (34.8 minutes) and Uro2 residents (33.7 minutes). There was a statistically significant difference (p < 0.05) in intraoperative FT between Uro1 (53.1 seconds) and Uro2 (33.1 seconds).

Table 3 displays variables with significant correlation to FT. Positive correlations were noted for OT, stone size, use of ureteral dilation, and use of a ureteral access sheath. Negative correlations were noted for the presence of a preoperative stent, resident year of training, and resident month of training.

MLR was performed on variables with significant correlations (Table 3). The model had a correlation coefficient of R = 0.510. OT (0.423, p < 0.05), the use of ureteral dilation (0.229, p < 0.05), and the presence of a preoperative stent (−0.210, p < 0.05) were significant predictors of intraoperative fluoro use.

Discussion

We have presented the largest database evaluating fluoro use during URSs at a residency program. Our findings demonstrate that fluoro use is highest toward the beginning of training, and is reduced as experience is gained. With knowledge of this tendency for residents to use prolonged FT during the Uro1 year, greater emphasis can be placed on reducing radiation exposure early during training.

The 5-year recurrence rate for urinary stones is 50%, and as high as 75%> 20 years. ²² One study found that on average, 1.77 CT scans were performed per URS intervention, leading to a mean cumulative ED for patients of 35.4 mSv per intervention. ²³ Of note, CT urography delivers an average ED of 34.5 mSv per scan, ²⁴ and a noncontrast abdomen–pelvis CT delivers an average ED of 15 mSv per scan. ²⁵ The ED from intraoperative fluoro itself ranges from 0.67 to 2.23 mSv per URS procedure. Including all medical radiation exposures, an estimated 20% of patients receive >50 mSv for the first year of follow-up. ⁵ The prevalence of stones has increased from 3% in 1976 to 9% in 2010, which translates to 1 in 11 persons in the United States being affected in their lifetime. ²⁶ With this increasing prevalence, high use of axial imaging, and patients often requiring multiple procedures, it is paramount to limit radiation exposure wherever possible.

As residents gain experience in the OR, less fluoro is used during URS. Two previous reports have demonstrated URS FT decreases with experience, as measured by resident case number, for the first 2 years of training. ^6,10 Similarly, we found that decreasing FT was correlated with months of training for the first 3 years of residency. Consistent with one previous report, ¹⁰ we found that Uro2 residents used less fluoro than Uro1 residents. This is the first report, however, to identify no change in fluoro use between Uro2 and Uro3 trainees. Mean FT used by Uro2 and Uro3 residents was identical, but Uro3 FT did not differ significantly from Uro1, likely because of a smaller sample of Uro3 cases. These findings suggest that the learning curve associated with fluoro use during URS may occur predominantly within the first year of training. Attendings were found to use slightly more fluoro than Uro2 and Uro3 residents, but this difference was not significant. We hypothesize that this increase in FT for attendings operating on their own in a community hospital setting may be because of a tendency to use more fluoro when less experienced personnel are assisting.

Several additional factors were found to be significant predictors of increased FT. In agreement with previous reports, prolonged FT was associated with the placement of a ureteral access sheath, ^6,7,10 ureteral dilation, ^6,7,10,21 larger stone size, ^6,7,21 and greater total OT. ^7,8,10,21 We also report that the presence of a preoperative stent was a negative predictor for FT. In contrast, one group found that a preoperative stent was a positive predictor for FT, ⁶ and others have found that it is not associated with FT. ^7,8,11,21 In our experience, the presence of a preoperative stent likely decreases FT by providing established access to the upper tract and navigation through a dilated ureter. With knowledge of these factors, greater emphasis can be placed on using and teaching techniques that limit FT, particularly during cases who require dilation or an access sheath. It should be noted that when controlling for OT in our regression analysis, PGY was not a significant predictor of FT. Therefore, additional focus should be on decreasing total time spent in the OR for all levels.

There are several potential limitations to this study. Because the study was retrospective, all data were collected from medical records. Our analysis included URS procedures both with and without stones. If relationships between variables and FT exist that are dependent upon stone removal, they may have been masked by the inclusion of data from URS for other indications. This possibility is worth noting, but is unlikely because fluoro is predominantly used for navigation of the urinary system, and additional predictors for FT such as access sheath placement, dilation, and total OT were corroborated by previous studies that focused on URS for urolithiasis. ^6,7,10 Another potential limitation is that procedures were performed by two attendings, and multiple residents in each year of the program. We believe that both attendings are well beyond the learning curve for URS, however, fluoro use has been shown to differ greatly between individuals with the same experience. ⁷ Lastly, no data were available regarding radiation dose delivered to the patient. An exact dosage would ascertain how operative experience and behaviors impact radiation exposure, and may make surgeons more cognizant of fluoro use. ¹⁰ FT is commonly accepted as a reliable indicator for relative radiation exposure, ^10,11 and we believe that it is sufficient to evaluate the effect of experience on fluoro use.

It is important to note that decreasing FT offers only a relative reduction in radiation exposure, as other factors such as BMI, patient positioning, and C-arm settings also affect radiation dose ^6,17,14 Although unlikely that urologists will exceed regulatory annual thresholds for radiation exposure, ²⁷ low dose radiation has the potential to cause harm. It, therefore, is important to identify behaviors that predict prolonged FT and teach techniques to decrease FT, in accordance with as low as reasonably achievable principles. ⁵ Minimizing FT is also a concern for specialties such as orthopedics ¹⁶ or interventional cardiology. ²⁸ Other recurring procedures, such as coronary angiography, require more FT than URS. ²⁸ Trainees in other specialties may, therefore, also benefit from the identification of trends or behaviors that predict prolonged FT.

Conclusion

We have evaluated fluoro use during URS in a residency program. We identified that fluoro use decreases with experience; however, we have shown for the first time that this learning curve likely occurs during the first year of training. Previous studies have evaluated URS fluoro use in residency training programs, ^6,7,10,12,21 but their analyses were limited to a single cohort of trainees at the same experience level, or limited to just the PGY1 and PGY2 years. Our data provide a more complete picture of the effect of resident experience on fluoro use. Given these findings, greater efforts should be placed on teaching Uro1 residents operative behaviors that will reduce FT early during training. In addition, urologists should be aware of the trend for factors such as access sheath placement, ureteral dilation, stone size, and operating time to increase FT. Efforts to reduce fluoro use ultimately will limit radiation exposure and improve safety for both patients and health care staff.