Radiation dose evaluations during radiological contrast studies in patients with morbid obesity

The purpose of this study was to evaluate the radiation dose to patients during radiological contrast studies performed after vertical banded gastroplasty (VBG) or Roux-en-Y gastric bypass (RYGBP) surgery in patients with morbid obesity.

Dose evaluations were performed on a sample of 39 patients (32 women and 7 men) with a mean weight of 117 kg (range 68-175 kg) and a mean body mass index (BMI) of 43.7 (range 22.2-54.9). Between the second and seventh postoperative day, patients underwent radiological follow-up after oral administration of approximately 70 ml of water-soluble iodinated contrast material (Gastrografin) and images acquired in anteroposterior, right and left oblique projections with the patient upright and then supine. Exposure conditions, dose-area product (DAP) and entrance skin dose (ESD) were recorded for each procedure. On the basis of these data, the effective dose (ED) was calculated using simulation software based on the Monte Carlo method for determining the absorbed dose to organs. To assess the optimal exposure conditions and the dose contributions of fluoroscopy and radiography, the effective dose rates were also evaluated using Plexiglas phantoms of different thickness to simulate different patient sizes.

The phantom measurements showed a fourfold dose increase when passing from normal-sized patients to obese patients. Mean DAP value obtained from in-vivo measurements was 70 Gy cm(2) (range 17-147 Gy cm(2)), and mean effective dose was 21 mSv (range 5-45 mSv).

When performing radiological contrast studies in patients with morbid obesity, every possible precaution should be taken to minimise patient dose. Special care should be taken to evaluate justification of the radiological procedure.