Effect of a full and empty bladder on radiation dose to the uterus, ovaries and bladder from lumbar spine CT and X-ray examinations

This is a quantitative study of the effect of a full and empty bladder on t he position of the uterus, ovaries and bladder relative to the lumbar spine . Data are used to estimate the difference in radiation dose to these organ s from performing a lumbar spine CT investigation or a lateral lumbar spine radiograph with a full bladder compared with an empty bladder. 12 women of child-bearing age underwent pelvic magnetic resonance scans with full and empty bladders. The positions of the uterus, ovaries and bladder were match ed with the radiation dose distribution that would have occurred either sid e of the inferior boundary of the CT scan volume and the lateral lumbar spi ne radiograph. These radiation dose profiles were measured on phantoms usin g a combination of ionization chambers and thermoluminescent dosemeters. Wh en the bladder was emptied, the mean position of the endometrial cavity fun dal tip moved from 4.1 cm to 6.1 cm inferior to the centre of the L5/S1 dis c space, and from 0.87 cm to 1.12 cm anterior to the centre of the L5/S1 di sc space. This movement on micturation would have reduced the mean dose to the uterine internal fundal tip during a pelvic CT scan from 6.8 mGy to 3.9 mGy, which represents a mean reduction of 43% (range 12-67%). The mean dos e from a lateral lumbar spine examination would have been reduced from 197 mu Gy to 126 mu Gy. The change in ovary position results in the mean ovary dose being reduced by 48% for the lumbar spine CT scan and by 43% for a lat eral lumbar spine radiograph. When the bladder was emptied, the average pos ition of the bladder wall moved from 7.2 cm to 10.3 cm inferior to the L5/S 1 disc space. This change in bladder position reduces the mean dose to the wall of a full bladder from 5.7 mGy for a CT scan and 114 mu Gy for a lumba r spine radiograph to 2.2 mGy and 42 mu Gy, respectively, for an empty blad der.