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Study examines radiation dose estimates for pregnant women undergoing therapeutic ERCP

April 29, 2009

Pregnant women with gallstone disease may require immediate endoscopic intervention because of potentially life-threatening cholangitis (infection in the bile ducts) or gallstone pancreatitis (inflammation of the pancreas). The radiation exposure in endoscopic retrograde cholangiopancreatography (ERCP), which is used to treat these conditions, is a concern because fetal tissues are more susceptible to radiation injury. Researchers from Greece found that the radiation risks associated with ERCP procedures are not trivial and that accurate fetal dose estimation is now available regardless of patient body size, operating parameters, equipment used and gestational stage. The study appears in the April issue of GIE: Gastrointestinal Endoscopy, the monthly peer-reviewed scientific journal of the American Society for Gastrointestinal Endoscopy (ASGE).

Endoscopic retrograde cholangiopancreatography is a specialized technique used to study and treat problems of the ducts that drain the liver and pancreas. To reach the ducts, an endoscope is passed through the mouth, beyond the stomach and into the small intestine (duodenum). A thin tube is then inserted through the endoscope into the common bile duct and pancreatic duct connecting the liver and pancreas to the intestine. A contrast material (dye) is injected through the tube outlining those ducts as X-rays are taken. The X-rays can show narrowing or blockages in the ducts that may be due to a cancer, gallstones or other abnormalities. Radiation exposure is of obvious concern as developing fetal tissues are more susceptible to radiation injury.

During pregnancy, the most common indication for ERCP is treatment of choledocholithiasis (gallstones in the common bile duct). The occurrence of choledocholithiasis can reach up to 12 percent of the pregnant population and increases with gestational age. Given that symptomatic gallstone disease increases the risk of morbidity and mortality of both the fetus and mother, medical intervention often cannot be postponed pending delivery. Previous case series have demonstrated ERCP to be safe and effective during pregnancy.

Fetal doses are associated with exposure factors such as kilovolt peak (the peak voltage applied to an X-ray tube), tube filtration and the physique of the pregnant woman. Radiation dose is expressed as a milligray (mGy). A milligray is a unit of absorbed radiation equal to 0.001 gray. (A gray is the dose of one joule of energy absorbed per kilogram of matter, or 100 rad.) Because the gray is such a large unit, many radiation measurements are made in milligrays. Exposures from X-ray equipment are typically expressed in milligrays. National and international radiation protection authorities consider fetal radiation doses up to 1 mGy insignificant, while doses over 10 mGy are considered more relevant.

"Physicians should be able to estimate the fetal dose in all stages of gestation and inform any pregnant patient undergoing ERCP about the actual radiation risks to arrive at a prudent decision regarding the exposed fetus," said study lead author John Damilakis, MD, University of Crete, Greece. "The findings of this study show that fetal radiation risks associated with fluoroscopically (X-ray) guided ERCP performed on a pregnant patient cannot be disregarded. Nonradiation ERCP has been proposed as an alternative, especially for pregnant patients in an effort to decrease potential fetal risks. However, further studies are required to prove that the clinical efficiency of nonradiation ERCP remains at the same level with conventional fluoroscopically guided ERCP."

Patients and Methods

The aims of this study were to examine the potential for a fetus to receive a radiation dose greater than 10 mGy (the limit above which an accurate determination of fetal dose is required) from the ERCP procedure carried out for the mother and develop a method for the assessment of the fetal dose from ERCP procedures. Researchers examined 24 consecutive male and non-pregnant female patients who received therapeutic ERCP for conditions including cholangitis, choledocholithiasis, pancreatitis, stent extraction, and pancreatic and bile-duct tumors. It should be emphasized that none of these patients were pregnant or suspected of being pregnant, thus no measures to limit radiation exposure were taken. Based on the radiation exposure in these 24 non-pregnant patients, the radiation dose delivered to a theoretical fetus was then estimated. The estimation was performed using a Monte-Carlo-N-particle transport code, widely used to assess radiation dose distribution in the body by simulating radiologic examinations in mathematical phantoms.

Results

The radiation doses estimated for a theoretical fetus in these 24 ERCP procedures ranged from 3.4 to 55.9 mGy. The researchers provide tabulated data that then allow for calculation of the fetal radiation dose.

The data revealed that the fetal dose from ERCP procedures may occasionally exceed 10 mGy, a considerably greater value than previously reported. In cases with pregnant patients, special efforts should be made to minimize the fetal radiation burden. An accompanying editorial on this study by former ASGE Standards of Practice Committee Chair Todd H. Baron, MD, FASGE, division of gastroenterology and hepatology, and Beth A. Schueler, PhD, department of radiology, both from the Mayo Clinic College of Medicine, Rochester, Minn., appears in the April issue and offers a list of general rules for safe and effective fluoroscopy use to minimize radiation exposure during ERCP in pregnant women.

Researchers noted that limitations of the study included a source of error in the estimation of the fetal dose related to variations of fetus location and size from the average, especially during the second and third trimesters. Another limitation concerns risks related to ionizing radiation. The risks per unit dose are derived from epidemiologic studies on effects of individuals exposed to high levels of ionizing radiation, such as atomic bomb survivors, patients exposed to radiation for medical treatment and animal experiments. Radiation protection organizations assume that low-radiation doses are also associated with hazard risks. However, significant uncertainty exists about the risks associated with low-radiation doses.

American Society for Gastrointestinal Endoscopy