Schema of radiation exposure from direct and scattered radiation for the surgeon and surgical assistant
Standard diagnostic imaging for nephrolithiasis is mostly performed with non-contrast computed tomography (NCCT) . Currently, the effective dose (ED) for NCCT of the abdomen and pelvis is 4.5–5.0 mSv . The use of low-dose NCCT (LDCT) offers the advantage of less radiation exposure for the patients. A meta-analysis of LDCT studies revealed sensitivity and specificity of 96.6% and 94.9%, respectively, for diagnosing urolithiasis, which was comparable to that of NCCT . The mean ED for patients undergoing LDCT was reported at 1.40 mSV in men and 1.97 mSV in women. When body mass index (BMI) was considered, however, the sensitivity and specificity decreased to 50% and 89%, respectively, for those with BMI >30 kg/m2 . The American Urological Association currently recommends the standard NCCT value over the LDCT value when planning to address stones in obese patients (BMI >30 kg/m2) . Furthermore, current imaging advances have enabled the development of ultralow-dose iterative reconstruction algorithms, which preserve image quality at low doses, making it possible to evaluate urolithiasis. Ultralow-dose NCCT delivers an ED of <1 mSV, which is a lower ED than that with LDCT [14, 15].
The follow-up of patients on medical expulsive therapy or after procedures for nephrolithiasis have shown that standard imaging studies—plain radiography of the kidney-ureter-bladder (KUB) and ultrasonography (US)—are better modalities than NCCT in terms of radiation exposure and cost. The mean ED for KUB imaging is 0.5–1.0 mSv , and the patient is not exposed to any radiation when using US. Current guidelines recommend initial US for children with suspected urolithiasis to avoid being sensitized to ionizing radiation .
During procedures for managing nephrolithiasis, including retrograde intrarenal surgery and percutaneous nephrolithotomy (PCNL) , almost all patients are exposed to radiation by way of fluoroscopy. The radiation exposure associated with PCNL is generally higher than that with ureteroscopy (URS) for nephrolithiasis because of the prolonged fluoroscopy time (FT). A retrospective study revealed that the mean FT during PCNL was 7.09 ± 4.8 min and the mean ED of patients undergoing PCNL was 8.66 mSV . Furthermore, an increasing number of risk factors—radiation exposure during PCNL, high BMI, high stone burden, and more percutaneous tracts—were significantly associated with an increased radiation ED. Obese patients (BMI >30 kg/m2) required a more than twofold higher dose than normal weight patients (BMI <25 kg/m2) (6.49 vs 2.66 mSV, p < 0.001) .
Various techniques can be used to decrease radiation exposure during PCNL. Air retrograde pyelography with the patient in a prone position can clarify the calyceal anatomy of the puncture site. Consequently, the mean adjusted ED during PCNL was 4.45 mSV for air retrograde pyelography compared with 7.67 mSV for contrast retrograde pyelography. This finding is likely due to the increased density of the contrast medium, leading to automatic adjustment of the C-arm tube and tube voltage (lower tube voltage is needed when air is in the field) . Compared with fluoroscopic guidance to assist PCNL , US guidance reduces radiation exposure and is particularly beneficial for treating obese patients with renal stones . Furthermore, combined US/URS-assisted access for PCNL reduces the mean FT compared with that for conventional PCNL under fluoroscopy-guided access .
Generally, radiation exposure of patients with nephrolithiasis is significantly less during URS than during PCNL . One study found a median FT of 46.9 s and a median ED of 1.13 mSV per procedure . Another study found, in an anthropomorphic adult phantom, that during PCNL the mean ED rate (mSV/s) was significantly increased during URS in the obese model (BMI >30 kg/m2) compared with that of the nonobese model .
Typically, the surgeon’s experience influences fluoroscopic use during URS . Surgeons having extensive experience with fluoroscopic surgery have less radiation exposure than trainees due to the shorter FT during URS . Weld et al. investigated whether added training in safety, minimization, and awareness during radiation training for urology residents reduced the FT during URS for urolithiasis. The authors found that the residents exposed to this dedicated training had a 56% shorter mean FT than the same residents had shown earlier during their first 6 months of training (before the dedicated training) . Therefore, proper education about fluoroscopy and its protocols (e.g., tactile and visual feedback) reduces their radiation exposure . Similarly, for URS, the mean FT and entrance skin dose from before the radiation safety training protocols to afterward were −0.5 min and −0.1 mGy (34%), respectively . Other points of which to be aware include the fluoroscopy beam, which should be collimated with the area of interest. In addition, the image intensifier should be placed as close to the patient as possible, and a pulsed fluoroscopy mode should be used to minimize radiation exposure during PCNL and URS for nephrolithiasis [29, 30]. For URS, urologists found that pulsed fluoroscopy images were adequate and equivalent for most tasks during the surgery compared with continuous fluoroscopy images . Furthermore, a drape placed over or under the patient may help reduce radiation scatter. The key point for reducing patients’ radiation exposure, however, is the promotion of physician awareness of the risk of radiation exposure and the importance of radiation protection.
Radiation Protection for Surgeons and Medical Staff During Surgery
The major source of occupational radiation exposure for surgeons and the medical staff is the scattered radiation produced from interaction of the primary radiation beam with the patient’s body and the operating table during procedures (Fig. 4.1). Rarely, these personnel may also be exposed to direct radiation when their hands move into the fluoroscopy field between the X-ray tube and image intensifier.
Radiation scattering is divided into two types: backward and forward scattering. The backward scattering dose is approximately 20-fold as strong as the forward scattering dose . Shielding against scattered radiation is usually accomplished by wearing protective clothing. The standard lead protection protocol requires the use of 0.35-mm lead aprons, thyroid shields, and eyeglasses with lead lining for the operating surgeon and 0.25-mm lead aprons for other personnel . However, protection from scattered radiation by wearing protective clothes is incomplete, especially for the arms, eyes, feet, and brain.
The radiation exposure dose to the surgeon performing PCNL with a mean ED of 12.7 mSV per procedure is higher than that with 11.6 μSV during URS because of the longer FT and less distance between the source of radiation and the surgeon [8, 34]. Some investigators reported the mean fluoroscopy screening time during PCNL was 4.5–6.04 min (range 1.0–12.16 min) . Furthermore, the mean radiation exposures to the finger and eye of the surgeon were 0.28 mSv and 0.125 mSV, respectively, due to the nonuniform radiation exposure to the scattered radiation [36, 37]. Therefore, operators should also protect the hands and eyes from scattered radiation exposure using gloves and glasses with lead lining. Most endourologists perform the needle puncture under fluoroscopy for renal access. The operator who carries out the needle puncture under fluoroscopy often is exposed to direct irradiation. The operator must be aware of this behavior and that it presents a critical risk. The surgeon must take care not to come into the direct fluoroscopic radiation field. The US approach is more beneficial than the fluoroscopic approach for protecting surgeons from radiation exposure during PCNL. Yang et al. reported that using a radiation shield constructed from 0.5-mm lead sheeting effectively reduces the surgeon’s radiation exposure .