Thyroid dose rate assessment with thermoluminiscent dosimeters for patients during mammography

At the beginning quality controls of two mammography X ray units were made according to IAEA documents. They were: viewing conditions, voltage and kerm repeatability and accuracy, kerm and output repeatability and linearity, all of them using a Diavolt tester. Power compression, thickness compression, leakage radiation evaluation of the automatic exposure control, determination of mean glandular dose for 28 kV - 80 m As Mo-Mo and for a clinical condition for a PMMA slab of 45mm. The working protocol was to select women between 40-60 years with mixed breast, without hormone treatments or breast disease, breast compressed thickness cranio caudal view CC between 40 - 60 mm (average 53mm), and the mediolateral oblique view MLO have a nipple circumference less than 15 cm. Patients signed a written consent. Thermoluminiscent dosimeters TLDs capsules were placed above and below the right breast, non overlapping, and other capsule on the thyroid isthmus. Mean glandular dose were measured for CC plus MLO view of right breast and absorbed dose and effective dose for thyroid gland. TLDs background dosimeters were placed far away from X ray equipment. 15 women were studied with a digital GBA Mamograf Hf unit and 25 women with a GE Senographe 600T Senix HF unit. Automatic exposure control Molybdenum- Molybdenum. Dosimeters were calibrated using a FujiFilm mammography X ray unit from Roffo Institute and they were read at CAC - CNEA Personal Dosimetry Laboratory. Finally, both equipment passed the quality controls. Values of thyroid absorbed dose (30-380 μGy) were between 1 - 3% mean glandular dose of CC plus MLO ( 0 to 5 mGy) right breast and these results were consistent with previous. The same for effective thyroid dose (1-15 μSv). Dosimeters were not calibrated for scattering energy to evaluate thyroid dose. It would be better to do this calibration and to use TLD 200 because they are more sensitive. We thanks patients and technicians for being very cooperative. (author)