| Lead equivalent, which offers protection against x-rays, is rated with a 100 kV tube voltage in Japanese Industrial Standard(JIS)Z , "Testing method of lead equivalent for x-ray protective devices." However, the actual tube voltage in general diagnostic examinations(normal to special radiography; including computed tomography, CT)is 50 to 150 kV. Therefore, we measured whether the performance of current lead aprons(three products)and protective aprons using composite materials(two products)changes at 60 to 141 kV of tube voltage. Furthermore, we evaluated x-ray shielding performance by measuring the transmission ratio of scattered x-rays. The lead equivalent of two currently used lead aprons was almost the same at all voltages. However, in one currently used lead apron and both protective aprons made of composite materials, lead equivalent decreased rapidly when tube voltage exceeded 100 kV. The transmission ratio of scattered x-rays increased with increasing tube voltage in all of the protective aprons examined. Further, in all aprons examined, the transmission ratio of scattered x-rays declined with widening of the scatter angle. As mentioned above, the x-ray shielding performance of some x-ray protective aprons suddenly decreased at tube voltages over 100 kV. Thus the performance of x-ray protective aprons should be published, and JIS Z 4501 needs to be revised. |
