Gideon Richards

Radiation Exposure During Continuous and Pulsed Fluoroscopy

UNLABELLED Abstract Background and Purpose: Previous studies using pulsed fluoroscopy have shown variable effects on radiation exposure because of the ramp and trail effect in older C-arm systems. This study compares radiation delivered in pulsed and continuous modalities using a modern C-arm system. MATERIALS AND METHODS Thermoluminescent dosimeters (TLDs) positioned in three body locations directly measured radiation dose during simulated ureteroscopy. Thirty pedal activations were administered using a pulsed or continuous mode to visualize an implanted guidewire and a radiopaque stone. TLD absorbed radiation and image quality were compared between imaging modes. RESULTS Pulsed fluoroscopy delivered less radiation compared with continuous fluoroscopy at each site: Anterior skin (0.10 vs 0.26 mGy, P<0.001), kidney (0.15 vs 0.40 mGy, P<0.001), and posterior skin (0.92 vs 2.62 mGy, P<0.001). Mean fluoroscopy time differed between continuous and pulsed modes (12.5 vs 3.0 seconds; P<0.001). Fluoroscopy time positively correlated with radiation exposure at all sites: Anterior skin (0.017 mGy/s, R(2)=0.90), left kidney (0.026 mGy/s, R(2)=0.96), and posterior skin (0.18 mGy/sec, R(2)=0.98). When evaluated by blinded urologists, 100% of reviewers felt pulsed images were adequate to identify guidewire position and 90.5% felt pulsed images were adequate for stone localization. CONCLUSION Pulsed fluoroscopy reduced fluoroscopy time by 76% and radiation dose by 64% compared with continuous fluoroscopy. Pulsed fluoroscopy images were adequate for most tasks of ureteroscopy and should be considered for reduction of radiation during ureteroscopy.

Ureteral Calculi Detection Using Low Dose Computerized Tomography Protocols is Compromised in Overweight and Underweight Patients

PURPOSE Low dose computerized tomography protocols have demonstrated a reduction in radiation exposure while maintaining excellent sensitivity and specificity in the detection of stones in patients of average size. Low dose computerized tomography protocols have not yet been evaluated in subjects in the extremes of weight. We evaluated the effect of body weight when using low dose protocols to detect ureteral calculi. MATERIALS AND METHODS Three cadavers of increasing weight (55, 85 and 115 kg) were prepared by inserting 721 calcium oxalate stones (range 3 to 7 mm) in 33 random configurations into urinary tracts. Cadavers were then scanned using a GE LightSpeed® at 7 radiation settings. An independent, blinded review by a radiologist was conducted to generate ROC curves, with areas under the curve compared using a 1-way ANOVA (α = 0.05). RESULTS Sensitivity and specificity were significantly lower in the low and high weight cadavers compared to the medium weight cadaver at 5 mAs (p <0.001) and 7.5 mAs (p = 0.048). Differences in sensitivity and specificity at radiation settings of 15 mAs or greater were not significant. CONCLUSIONS The sensitivity and specificity for the detection of ureteral calculi on computerized tomography were decreased for underweight and overweight subjects when using extremely low dose radiation settings (less than 1 mSv). Low dose protocols of 15 mAs (2 mSv) can still be used for these subjects without jeopardizing the ability to identify ureteral stones.

Prostate Specific Antigen Levels and Prostate Cancer Detection Rates in Patients With End Stage Renal Disease

PURPOSE Patients with end stage renal disease plus prostate cancer are ineligible to receive a renal transplant at most centers until an acceptable cancer-free period is demonstrated. To our knowledge previously established prostate specific antigen reference ranges have not been validated in patients with end stage renal disease. We determined age stratified 95th percentile prostate specific antigen reference ranges and the prostate cancer detection rate at specific prostate specific antigen intervals for patients with end stage renal disease. MATERIALS AND METHODS We retrospectively reviewed the records of 775 male patients with end stage renal disease on the waiting list for a renal transplant who had undergone a serum prostate specific antigen test. Prostate specific antigen was stratified by age at the time of the blood test and 95th percentile reference ranges were calculated for each decade. A total of 80 patients underwent prostate biopsy for increased prostate specific antigen and/or abnormal digital rectal examination. The cancer detection rate was calculated for specific prostate specific antigen reference ranges. RESULTS The age specific 95th percentile prostate specific antigen references ranges were 0 to 4.0 ng/ml for ages 40 to 49 in 137 patients, 0 to 5.3 ng/ml for ages 50 to 59 in 257, 0 to 10.5 ng/ml for ages 60 to 69 in 265 and 0 to 16.6 ng/ml for ages 70 to 79 years in 69. The cancer detection rate was 44%, 38% and 67% for prostate specific antigen 2.5 to 4.0, 4 to 10 and greater than 10 ng/ml, respectively. CONCLUSIONS In our study population of patients with end stage renal disease age stratified prostate specific antigen was higher than in the general population. The cancer detection rate was increased in our patients with end stage renal disease compared to that in patients with normal renal function at specific prostate specific antigen intervals. Lower prostate specific antigen cutoffs may be appropriate to recommend prostate biopsy in patients with end stage renal disease.

Hybrid Transureteral Nephrectomy in a Survival Porcine Model

Background and Objectives: Natural-orifice approaches for nephrectomy have included access via the stomach, vagina, bladder, and rectum. Recently, the feasibility of using the ureter as a natural orifice for natural-orifice transluminal endoscopic surgery nephrectomy has been demonstrated in a nonsurvival porcine model. The purpose of this study was to assess the outcomes of transureteral laparoscopic natural-orifice transluminal endoscopic surgery nephrectomy in a survival porcine model. Methods: Three pigs underwent hybrid transureteral natural-orifice transluminal endoscopic surgery nephrectomy. An experimental balloon/dilating sheath was inserted over a wire to dilate the urethra, ureteral orifice, and ureter. Through a bariatric 12-mm laparoscopic port, the ureter was opened medially and the hilar dissection was performed. Next, 2 needlescopic ports were placed transabdominally to facilitate hilar transection. The kidney was morcellated using a bipolar sealing device and extracted via the ureter using the housing of a bariatric stapling device. The ureteral orifice was closed with a laparoscopic suturing device. The bladder was drained by a catheter for 10 to 14 days postoperatively. Pigs were euthanized on postoperative day 21. Results: All surgical procedures were successfully completed, with no intraoperative complications. One pig had an episode of postoperative clot retention that resolved with catheter irrigation. Each pig was healthy and eating a normal diet prior to euthanasia. Conclusions: This study demonstrates the feasibility of a hybrid transureteral approach to nephrectomy in a survival porcine model. This technique avoids the intentional violation of a second organ system and the risk for peritoneal contamination. Improved instrumentation is needed prior to implementation in the human population.

2220 RADIATION EXPOSURE DURING CONTINUOUS VERSUS PULSED FLUOROSCOPY

INTRODUCTION AND OBJECTIVES: There are multiple modalities to produce and capture fluoroscopic images, including continuous and pulsed modes. Continuous fluoroscopy allows for real-time imaging but could deliver larger radiation doses to the patient. Pulsed fluoroscopy delivers bursts of radiation at set intervals, reducing fluoroscopy times. Despite this reduction in times, studies have shown no difference in effective dose when comparing pulsed fluoroscopy to continuous fluoroscopy due to the “ramp and trail effect”. Newer X-ray tubes can now deliver a more uniform current in a pulsed fashion while reducing unwanted radiation by minimizing this effect. The purpose of this study is to directly compare the amount of radiation delivered under pulsed fluoroscopy against continuous fluoroscopy in a modern C-arm system. METHODS: Thermoluminescent dosimeters (TLDs) were implanted at 3 sites in a female human cadaver to directly measure radiation dose, including the left kidney, posterior skin, and anterior skin. While in the supine position, the cadaver received 30 pedal activations either in the continuous or pulsed mode (1 pulse/sec) using a modern C-arm at 69 kVp and 1.51 mAs to visualize an implanted guide wire and a radio-opaque stone. The amount of radiation absorbed by the TLDs was recorded. Data was analyzed using a paired two-tailed Student’s t-test ( 0.05), Wilcoxon Signed Ranks procedure, and least-squares analysis. RESULTS: Pulsed fluoroscopy delivered lower doses of radiation compared to continuous fluoroscopy at each site examined: anterior skin (0.10 vs 0.26 mGy, p 0.001), kidney (0.15 vs 0.40 mGy, p 0.001), and posterior skin (0.92 vs 2.62 mGy, p 0.001). Mean fluoroscopy time differed significantly between continuous (12.5 s, range 12.2–13.7 s) and pulsed (3.0 s, range 2.9–3.0 s; p 0.001). Fluoroscopy time positively correlated with radiation exposure at all sites: anterior skin (0.017 mGy/sec, R 0.90), left kidney (0.026 mGy/ sec, R 0.96), and posterior skin (0.18 mGy/sec, R 0.98). However, pulsed mode delivered more radiation per second of fluoroscopy time compared to continuous mode overall and at all sites (p 0.001). CONCLUSIONS: When using fluoroscopy, pulsed images significantly reduce radiation exposure compared to continuous fluoroscopy. Using the same pedal activation time, continuous mode resulted in significantly longer fluoroscopy times compared to pulsed mode. These longer fluoroscopy times outweighed the higher dose per second delivered by the pulsed fluoroscopy mode. Thus, pulsed fluoroscopy could be used to minimize radiation exposure to patients whenever appropriate.

1076 DETEMINATION OF PATIENT RADIATION DOSE IN RADIOFREQUENCY AND CRYOABLATION OF SMALL RENAL MASSES

INTRODUCTION AND OBJECTIVES: Percutaneous radiofrequency ablation (RFA) and percutaneous cryoablation (Cryo) are minimally invasive alternatives employed in the treatment of small renal masses. Although studies reporting complications and efficacy have been published, no prior study has determined the patient radiation dosage received with these two procedures. The purpose of this study is to compare the radiation exposure received in patients treated with percutaneous RFA and Cryo. METHODS: An institutional review board approved retrospective review of patients undergoing RFA or Cryo between 2004 and 2010 was performed. The number of CT scans performed during probe placement and treatment was measured. Radiation dose was measured in mGy-cm and was recorded as the dose length product (DLP) by the GE Lightspeed VCT scanner (64 slice). Groups were compared using the Mann-Whitney-U test. RESULTS: Fifty-six patients with small renal masses were treated with a percutaneous ablative technique (24 RFA and 32 cryo). The mean number CT scans was 13.7 and the mean dose was 2086 mGy-cm in all patients. When the two modalities were compared there was no significant difference in age, ASA score, tumor size, complication rate or success rate. The treatment time in minutes (80.4 vs. 66.8; p 0.001), and number of probes utilized (3.4 vs. 1.3; p 0.001), was greater for Cryo compared to RFA patients. The amount of radiation received by both groups was significant and equivalent to approximately two full CT scans of the abdomen and pelvis. There were also a greater number of CT scans (16.4 vs. 10.9; p 0.01) and higher mean DLP (2374 vs. 1460 mGy-cm; p 0.05) for Cryo compared to RFA. CONCLUSIONS: Patients undergoing both percutaneous RFA and cryo are exposed to significant radiation exposures during treatment. These relatively high radiation exposures must be considered, particularly when applying these modalities to younger patients. Efforts designed to reduce radiation dose during treatment should be developed.