Lead apron attenuation: Bushong lists 75% to 88% for 0.5 mm Pb at 100 and 75 kVp, but other sources run higher

There isn’t one correct percentage. Good sources disagree, so learn the direction first: more lead means more protection, and higher kVp means less.

What does the textbook table say?

Bushong’s table, repeated in Sherer:

Lead equivalent	50 kVp	75 kVp	100 kVp	Weight
0.25 mm Pb	97%	66%	51%	1 to 5 kg
0.50 mm Pb	99.9%	88%	75%	3 to 7 kg
1.00 mm Pb	99.9%	99%	94%	5 to 12 kg

Why do other sources say about 97%?

Other sources report much higher figures than that table:

• Livingstone and Varghese (2018) measured a mean of 97% for 0.5 mm aprons and 90% for 0.25 mm aprons, at 100 kVp.
• Sherer itself reports about 3.2% transmission through a 0.5 mm apron at 100 kVp, or about 97% attenuation. That sits in the same book as the 75% table.
• Bontrager says a 0.5 mm apron reduces exposure by a factor of 50 over the diagnostic x-ray range. That works out to about 98%, with no kVp or beam stated.

The 2018 study and Sherer’s figure are of a direct beam. Neither is a scatter figure, and aprons mostly face scatter. Bushong’s table states no beam condition, so it may not be measuring the same thing. We can’t tell you which number an exam item would use. ARRT® says it avoids content where resources conflict, and its outline lists “attenuation properties” without numbers. If your program teaches the table, know the table.

An earlier version of this page told you 95% to 99% was a myth for a 0.5 mm apron. The measurements don’t support saying that.

Is there a federal minimum?

None that we found in 21 CFR Part 1020 or 10 CFR Part 20. An earlier version of this page claimed 21 CFR 1020.32 set 0.5 mm. That section is about equipment and never mentions aprons. See our thyroid shield page for what it does cover.

The Health Physics Society says minimums are set in state regulations, commonly 0.25 or 0.5 mm. We didn’t open any state regulation. ARRT’s outline points to NCRP Report 102 for minimum lead equivalents. We read a public copy: it says protective aprons of at least 0.5 mm lead equivalent shall be worn in the fluoroscopy room by each person except the patient. Our text search found no 0.25 mm apron minimum there, so that figure comes from textbooks. By source:

• Apron, minimum: 0.25 mm Pb (Bushong, Sherer).
• Apron, fluoroscopy and interventional: 0.5 mm Pb (NCRP Report 102 for fluoroscopy, Sherer).
• Gloves: at least 0.25 mm Pb when hands are near the field (Sherer). NCRP Report 102 says a fluoroscopist’s hand shall not be placed in the useful beam unless the beam is attenuated by the patient and a protective glove of at least 0.25 mm lead equivalent.

These match our Radiation Protection guide. Many facilities stock only 0.5 mm so nobody picks the wrong one. Sherer calls it a good balance of protection and weight.

What else do you need to know?

• Wraparound aprons make sense if your back may face the source.
• Storage: hang aprons on a rack. Folding them can crack the lead.
• Checks: Bushong says to fluoroscope aprons and gloves for cracks at least once a year, and that apparel with cracks, tears or holes may require replacement. Our advice: stop using a cracked one and report it.

The physics is in the Radiation Physics and Radiobiology chapter. Drill the rest with the Radiation Protection practice set.