In this study, we demonstrate that a low-dose fluoroscopy protocol significantly reduced patient radiation exposure without affecting clinical outcomes such as operative time, fluoroscopy time, stone-free rate or complications suggesting that the LD protocol can provide safe and efficient fluoroscopy guidance during PCNL without compromising patient outcomes. These results were obtained and remain significant without any selection bias with regards to BMI. From the multivariable regression models, these data support the known association between higher STCD and higher operative times. Additionally, a higher preoperative stone burden was associated with longer operative time and lower odds of postoperative SFS.
Impetus for change came from anecdotal observation that PCNL cases resulted in significant radiation exposure to the patient. From the surgeon’s experience, applying the low-dose fluoroscopy technique caused a slight readjustment to the workflow. However, by the end of the first case, the surgeon and assistants were comfortable with using the technique. Residents had difficulty using 4PPS during needle access, and thus 8PPS was used, which was felt to be adequate.
Vassileva et al. described radiation exposure associated with endourologic procedures with data from several centers. In this analysis, four centers reported average radiation exposure during PCNL of ranging from 27.0 mGy to 58.4 mGy [4]. This is comparable to the standard dose protocol used in our study. Implementation of the LD protocol led to a four-fold decrease in total radiation exposure in our study.
In the era of ALARA and increased awareness of the potential dangers of ionizing radiation, fluoroscopy guidance in PCNL has come under scrutiny as a target for improvement and optimization. To this end, several groups have reported the use of ultrasound-guided access and dilation. In general, fluoroscopy is still used for the dilation and drainage tube placement portions. Zampini et al. reported a mean radiation dose of 14.21 and 14.67 mGy with ultrasound-guided percutaneous access with prone and supine positions, respectively, while Chi et al. reporting a mean radiation dose of 3.1 ± 3.2 mGy with fluoroscopy only used for nephrostomy tube placement[5, 6]. In Zampini’s study, on average patients had a BMI of 27.28 and 29.60 for the prone and supine positions respectively. They also reported a STCD of 91.3 mm and 83.7 mm for the prone and supine groups respectively. In this study, we demonstrate that using the low dose protocol in an initial cohort of 31 patients brought the cumulative radiation exposure to 11.68 ± 7.01 mGy. We also saw that the last fifteen of these had only approximately 9 mGy of radiation exposure, suggesting that the low dose protocol can be further optimized. Despite a mildly higher BMI and STCD in our study, we were able to achieve a lower cumulative radiation dose. The results of our study may be especially relevant to practice settings where acquisition of additional and oftentimes expensive ultrasound equipment represents a significant potential investment.
Bayne et al showed that higher BMI was associated with a more challenging learning curve for ultrasound guided PCNL[7]. Of note, the mean BMI was 32 ± 7.7 (standard 30; LD 32) in our cohort, with the average patient meeting the “obese” definition. In the Chi et al. study, the average BMI was 26, possibly decreasing ability to generalize conclusions to a more obese population[5]. Furthermore, the lack of hydronephrosis and presence of staghorn calculi have been associated with less successful ultrasound PCNL access[8, 9]. Our data support the utility of a low-dose fluoroscopy protocol, which does not require training in use of a separate technology and is equally effective in obese and morbidly obese patients. Clinical outcomes and rate of success of percutaneous access were unchanged when using the LD protocol.
In a study from Elkoushy et al, using pulsed fluoroscopy with a pulsed frequency of 4 frames per second on PCNL was associated with a decrease in fluoroscopy time compared to continuous fluoroscopy of 30 frames per second (341.1 vs 121.5 sec, p < 0.001)[10]. Fluoroscopy time was used in this study as a surrogate for radiation dose. The data presented here support the conclusion that decreased fluoroscopy frame rate can reduce intraoperative radiation exposure.
The limitations of this study include its single institution, single surgeon, and unblinded nature. Other potential bias that may have occurred from the study include the Hawthorne effect since the protocol change was made outside of a controlled experiment. An overall cohort of 100 subjects may limit the power of the statistical analysis. Surgeon preference at this institution is to pursue upper pole access when safe to do so. As such, there were few observations for the middle and lower pole accesses (6 in the standard treatment protocol, and 3 in the LD). These data suggest the feasibility of low-dose radiation protocols reducing radiation without compromising clinical outcomes or requiring use of a separate imaging modality.
Future investigations should test this protocol in a prospective, randomized fashion to ensure consistency of results. Expanding the study design to include additional surgeons and multiple institutions would further corroborate the results. A more aggressive reduction of the frame rate to 2 PPS for most of the case would further reduce radiation exposure[10, 11]. In the experience of the surgeon, while 4 PPS is feasible for most straightforward needle punctures in experienced hands, there is an anecdotally higher risk of requiring more than one puncture (and therefore higher radiation exposure) when residents or fellows are being trained. Based on previous literature, comprehensive preoperative review of imaging and the use of end-expiration timed fluoroscopy in combination with the low-dose fluoroscopy protocol should yield great reductions in cumulative radiation exposure[12].