RSNA 2018: Digital X-Ray Preview

X-ray tube scatter greatly adds to radiation exposure

By Wayne Forrest, AuntMinnie.com contributing writer

November 7, 2018 --

Tuesday, November 27 | 3:30 p.m.-3:40 p.m. | SSJ21-04 | Room N229
How much does x-ray tube scatter contribute to radiation dose exposure for nearby clinicians and other staff? More than previously thought, according to this study from researchers at the Mayo Clinic in Rochester MN.

Current radiation safety practices are based on the belief that the primary source of occupational radiation dose for interventional radiologists is the patient. However, these findings point to the imaging device itself as the radiation source that poses the greatest threat.

The researchers measured air kerma (KA) to the average location of the upper body of an interventional physician with and without a phantom positioned in the path of the x-ray beam. Kerma stands for kinetic energy released per unit mass. In radiology, it is the measure of energy transferred from radiation to matter, such as a nearby human.

For their experiment, the researchers used geometry that was consistent with an imaging protocol for thoracic and abdominal interventional procedures. The setup also allowed the group to isolate the radiation dose emitting from the phantom, rather than directly from the x-ray tube.

Ashley Tao, PhD, a medical physics resident, and colleagues looked at the scatter from three different manufacturers' x-ray tubes. The systems were configured to produce similar beams and an equivalent magnitude of scatter originating from within the phantom for all systems.

The analysis revealed that x-ray scatter coming from the x-ray collimator contributed substantially to the radiation dose measured at the hypothetical location of the interventional physician's upper torso. The researchers also observed a minimum of 20% tube scatter at all distances from the central axis of the x-ray beam.

"Considering all x-ray tubes and variable distance from the central x-ray, scatter emitting from the beam exit window of the tubes accounted for 20% to 55% of the total scatter," they noted.