P102] Maximum dose to the thyroid organ assessment using APD UNFORS EDD-30 for patients submitted to mammography examinations

Abstract

Purpose We characterized the active personal dosimeter EDD-30 based on a set of tests: dose and dose rate linearity, energy dependency, reproducibility and angular dependency to use in radiation protection and access the maximum dose in thyroid organ in patients submitted to mammography screening examinations. Methods Measurements were performed with two UNFORS dosimeters: reference XiO detector and EDD-30, set together on the surface of a Perspex phantom, using the X-ray beam of a mobile and mammography units. EDD-30 readings, Hp”(10) were obtained using the EDD-30 in the surface of NM thyroid phantom placed on top of the trunk of the anthropomorphic phantom Alderson RANDO and using CIRS BR12 slabs (50% glandularity) to simulate compressed breast thicknesses (t) in range 20–80 mm. Set up: cranium caudal (CC) view with AOP STANDARD mode; Mean air kerma at the entrance surface of the neck in the thyroid location, K i 0 = Hp ″ ( 10 ) · F Hp ( 10 ) / Hp ′ ( 10 ) · F Angle · F Energy · J mGy / mSv , F’s are correction factors and J converts Hp(10) to incident air kerma, IAK; Mean incident air kerma in thyroid organ, K i T , was obtained using K i T = K i 0 exp ( - μ PMMA · x ) , x = 0,8 cm, μ PMMA – linear attenuation coefficient of PMMA for Compton scatter beam energy. To obtain the maximum dose to the thyroid organ, H T , we considered the following approximations: medio-lateral-oblique view with a 10% increase in H T and MGD, relative to CC view, and K i T ⩾ H T . Results APD is linear in the dose rates interval 13 mSv/h - 2.0 Sv/h with relative response, r = 1.22 ± 6% (k = 2). Energy response and angle dependence are in accordance with manufacturer data, r ≅ 1.2 in the energy range 28–40 keV; r ≈ 0.8 for angles above 60 degrees. Maximum normalized absorbed dose in thyroid for a CC view (Ht/mAs) range: 0.006–0.024 μ Gy/mAs; In bilateral exam: 0.05 maximum Relative Organ Dose for the thyroid, ROD (Ht/MGD) range: 0.02–0.12 %. Conclusions Using a very different method, we reproduced the results obtained by Sechopoulos (Monte Carlo Simulation), and Hatziioannou (TLD readings). Thyroid organ dose for a mammography screening examination of an average breast (t = 55 mm) is very low (3,4 μ Gy) corresponding to approximately 30 min of exposure to natural radiation. No thyroid protection is recommended.