Abdominal shields are not routinely used when chest x-ray exams are performed. Should they be, to make this most commonly ordered radiology procedure safer for patients? The answer is “no”, according to a detailed assessment published in the October issue of the British Journal of Radiology.
The study conducted by medical physicists at Royal Adelaide Hospital in Adelaide, Australia, showed that abdominal shields provide very little protection to shielded organs from radiation dose exposure during a posteroanterior (PA) chest radiograph. The best protection for a patient remains use of appropriate collimation of the x-ray beam and optimal setting of imaging parameters.
These newly published findings may benefit radiology departments dealing with patients who inquire about or request out-of-plane shielding, similar to what they may experience when having dental x-rays. Abdominal shields used with chest x-ray exams complicate and potentially compromise the diagnostic integrity of acquired images.
Yuri V. Matyagin, PhD, and Peter J. Collins, of South Australian Medical Imaging, conducted a study to assess the effectiveness of abdominal lead shields in reducing the radiation dose to adjacent shielded organs. They also evaluated factors contributing to dose under the shield. The use of Monte Carlo simulation enabled the authors to evaluate internal and external scatter separately.
Radiographic exposures were simulated to a soft-tissue phantom of 80x34x24 cm (length, width, thickness) at a peak x-ray tube voltage of 100 kV. The abdominal shield was simulated as 0.5 mm lead with and without a 0.2 mm thick plastic firm cover. The shield-to-phantom spacing varied from 0 to 40 cm.
The major contribution to radiation dose exposure to shielded organs comes from photons scattered internally from within the primary beam region of the patient. The authors determined that, in general, the shield provided a small reduction in absolute dose in the regions it protected. The dose reduction was about 4% (or 0.035 µGy) at a depth and location from the x-ray field corresponding to the level of the uterus and ovaries. The dose reduction in relative dose terms were greater for sections of the phantom away from the x-ray field and especially in low-depth regions. The shield was most effective when it was positioned snugly on the phantom with no gaps.
Based on their detailed findings published in the article, the authors confirmed that abdominal shields provide very little dose reduction benefit. They did recommend that if an abdominal shield is ever used, it should be positioned as close as possible to the surface of a patient to reduce radiation scattered in from passing under the shield.
Value of abdominal shield use during chest x-ray exam is negligible. Appl Radiol.