Reduction in patient skin dose during interventional radiology with the use of an air gap substitute

Scattered radiation is inevitably generated in the patient couch during interventional radiology (IVR) procedures that use an under-couch tube system. Most of this scatter reaches the patient's skin surface and results in an increase in the skin dose without contributing to the diagnostic image. We considered that this unnecessary exposure could be reduced by the addition of an air gap between the couch and the patient. Because it is physically impossible to place an air gap on top of the couch and under the patient, we devised a new process in which an expanded polystyrene (EPS; ρ=0.0125 g cm^-3) board is used as a substitute for the air gap. The results show that the EPS board played an effective role in reducing the skin dose to the patient. Using an EPS board 6 cm thick as an air gap substitute resulted in skin dose savings of ∼9%. This method is easy to set up in clinical circumstances and is inexpensive. We recommend that this simple method of skin dose reduction be used for all IVR procedures.