| The results below are from an experiment to determine the best
position of lead protection during chest imaging to minimise gonad
dose. Data from a lab experiment looking at the posterior vs.
anterior shielding 'debate'. Bottom line, the vast majority of the
scatter gonads (and by extension, the fetus) get is from internal
scatter for which there is nothing to do. The controllable scatter
mostly comes from the IR and the wall anteriorly. Some of us
have been around long enough to know that we started shielding
posteriorly because RT often failed to collimate to the IR back in
the bad old days. Posterior shielding was in lieu of good
practice, in other words. When properly collimated, there is very
little scatter from the posterior.
LAB DATA:
|
Technical/Shielding Factors |
mR |
% change in dose |
| Male gonads |
100 kVp, no shielding, collimated |
0.8 |
|
| Male gonads |
100 kVp, posterior shielding, collimated |
0.6 |
-25% |
| Male gonads |
100 kVp, anterior shielding, collimated |
0.5 |
-37.5% |
| Male gonads |
100 kVp, shielding inside phantom, collimated |
0.3 |
-62.5% |
| Male gonads |
100 kVp, no shielding, open field |
10.0 |
+1250% |
|
|
|
|
| Female gonads |
100 kVp, no shielding, collimated |
2.1 |
|
| Female gonads |
100 kVp, posterior shielding, collimated |
1.7 |
-19% |
| Female gonads |
100 kVp, anterior shielding, collimated |
1.3 |
-38.1% |
| Female gonads |
100 kVp, shielding inside phantom, collimated |
0.8 |
-62% |
| Female gonads |
100 kVp, no shielding, open field |
22.0 |
+1046% |
The data were obtained by use of a 3M chest and abdomen phantom
in upright position in front of an chest IR. Dosimeters were
placed in the gonad positions. Shielding was 1) not used, 2) used
posteriorly, 3) used anteriorly, 4) used internally between chest
and abdomen, and 5) no shielding with primary beam overlapping
gonads (no collimation).
As you can see, placing a shielding INSIDE the patient does the
most good but I would not recommend it. Posterior shielding does
some good but not as much as anterior shielding. So, if we can
only shield one side, anterior is better but it is always better
to over-shield then under-shield.
Data kindly supplied by
Dr. Elwin Tilson
Dept. of Radiologic Sciences
Armstrong Atlantic St.Univ
Savannah, GA 31419
www.radsci.armstrong.edu/el/
|
