Understanding Absorbed Radiation Dose in Voiding Cystourethrogram

A new study led by Rajeev Chaudhry, MD, assistant professor of urology in the Division of Pediatric Urology at UPMC Children’s Hospital of Pittsburgh, prospectively examined the absorbed radiation dose in pediatric patients undergoing a fluoroscopic voiding cystourethrogram (VCUG). 

This is the first study conducted in pediatric patients to measure actual absorbed dose at the level of the skin (sacrum) using dosimetry.

“Most of the literature studies and estimates of radiation exposure in pediatric patients undergoing fluoroscopic VCUG use either dose area product (DAP) or air kerma as a proxy for absorbed dose. These methodologies give an understanding of the exposure to the patient, but not an accurate measure of the actual amount of radiation absorbed at skin level,” says Dr. Chaudhry. 

Study Overview

VCUG has been the gold-standard test for diagnosing cases of vesicoureteral reflux, and as an investigatory diagnostic for assessing genitourinary abnormalities, hydronephrosis, and the function of the posterior urethral valve, among others.

Given the sensitivity of young children to ionizing radiation (10 times more sensitive than adults), and given the stochastic nature of radiation exposure and the potential cumulative burden and consequent increases in risk for malignancy, having as accurate a measure as possible of the absorbed radiation dose from VCUG in pediatric patients is paramount to help guide clinical practice and counsel families of young children.

“While there are other imaging modalities being deployed more frequently as substitutes for or adjuncts  to VCUG – for example MAG-3 scans and contrast-enhanced ultrasonography – these diagnostic modalities at present are either not widely adopted and available, and in some instances also introduce a dose of radiation. Given the relative ease and wide-spread use of fluoroscopic VCUG, our goal with this study was to arm clinicians and patients with the most accurate information possible about the radiation exposure from the test,” says Dr. Chaudhry.

For this study, single point dosimeters were applied to the enrolled patient’s (n=44) sacrum. During the VCUG procedures, all patients received the same fluoroscopy settings: low dose and three pulses per second from a distance of 54 cm from the source to the skin. The smallest possible area was used in conjunction with a tightly collimated x-ray beam. Apart from the study, these parameters are part of standard test protocols in place at UPMC Children’s for VCUG.

Key Findings and Clinical Implications

With the fluoroscopic settings employed in this study, image quality was not degraded or compromised, and the absorbed dose at the skin was low for a single VCUG procedure. The median absorbed dose in this patient cohort was 0.32 mGy, which translates to an effective whole-body dose of 0.04 mSv.

“To add context to the absorbed dose findings we found, a typical pelvic x-ray will expose the recipient to around 0.6 mSv. A CT scan is much higher with a range between 4.8 and 8.4 mSv. Ambient background radiation exposure from environmental factors is about 3 mSv a year,” says Dr. Chaudhry. “VCUGs at our institution, using our tightly controlled protocols for radiation exposure, afford a small dose of radiation to patients in a single exposure, while cumulatively the burden would also be low when comparing the absorbed dose to other modalities and against the yearly exposure recommendations from regulatory bodies.”

While the study was performed at a single institution with a relatively small patient cohort, the findings are suggestive of and support the safe use of VCUG in pediatric patients while limiting their exposure to the potential toxicities and morbidities of cumulative radiation exposure. Even with the advent of newer imaging modalities, VCUG will likely remain a standard of care. The data uncovered in this study by Dr. Chaudhry and colleagues will help arm pediatric urologists with a more accurate understanding of the potential radiation exposure to their patients.

Reference

Chaudhry R, Dangle PP, Cannon GM, Schneck X, Stephany HA. Prospective Evaluation of Radiation Dose With Conventional Fluoroscopic Voiding Cystourethrogram in Pediatric Patients. J Pediatr Urol. 2021; In Review.