Radiation exposure with spiral CT of the paranasal sinuses

Purpose: Determination of the radiation doses in spiral CT of the paranasal sinuses using a variety of mAs values and scan protocols. Material and met hods: CT examinations of the paranasal sinuses were performed using an Alde rson-Rando phantom. Radiation dose was determined by LiF-TLD at the level o f high risk organs in the head and neck region for combinations of differen t scan parameters (2/3, 3/3, 3/4 mm) and decreasing charges (200, 150, 100, 50, 25 mAs) on a spiral CT. Additional measurements were performed on thre e other CT scanners using the 2/3 mm protocol at 50 mAs, and a single slice technique (5/5 mm) on one scanner. Results: The lowest dose values found w ere 1.88 mGy for the eye Tenses, 1.35 mGy for the parotid gland, 0.03 mGy f or the thyroid gland and 0.1 mGy for the medulla oblongata using 2 mm colli mation and 3 mm table feed at 25 mAs. Maximal dose values resulted using th e 3/3 mm protocol at 200 mAs (31.00 mGy for the eye lense, 0.65 mGy for the thyroid gland). There were no significant differences found between the di fferent CT scanners. Conclusions: Using up-to-date CT scanners, radiation e xposure may be reduced by a factor of 15-20 compared to that of conventiona l CT technique. Thus, the exposure of the eye lens comes to only a thousand th of the value supposedly inducing a cataract, as published by the ICRP.