Introduction
Radiation protective lead apron is important device for radiation protection. There are several types of aprons. In the one-piece type of apron, there are two kinds of apron such as wrap around type and front coverage type. They are designed to prevent radiation exposure not on the back side but on the front side. This study was conducted to investigate the relationship between the type of lead apron and the radiation protective effect at the back side.

Method
We compared three groups of radiation exposure in back side with no lead apron (group C), front coverage type (group F) and wrap around type (group W). We put wrap around type apron on the bed and checked 40 times of C-arm fluoroscopy in each measurement (bedside table). We collected radiation absorbed dose (RAD), exposure time (ET), and effective dose (ED) of beside table, upper part of apron and lower part of apron. In each situation, we measured them 30 times.

Results
There was no statistically significant difference in RAD, ET, ED of the bedside table in the three groups. (p=0.269, 0.248, 0.593, respectively). In upper and lower part, EDs were statistically significant different in three groups. In group F, ED (0.8 0.4 μSv) of upper part was the highest. (group C: 0.2 0.4 μSv, group W: 0.0 0.0 μSv, p < 0.001) ED of lower part in group C (0.8 0.18 μSv) and F (0.9 0.3 μSv) were higher than that in group W (0.1 0.3 μSv, p=0.12)

Conclusion
In the upper part of apron, the radiation exposure of front coverage type apron was higher than that of wrap around type and even no apron. To reduce radiation exposure from the back side, wrap around type apron can be recommended.