Dose distribution in pediatric CT head examination: Phantom study

To keep radiation doses during computed tomography (CT) examinations as low as reasonably achievable, performing a detailed dose measurement is important. A flexible acrylic sheet roll CT dosimetry phantom (SRCT-P) with radiochromic film (RF) was developed to estimate in detail the dose distribution during pediatric CT examination. The SRCT-Ps were cylindrically-shaped by rolling up flexible acrylic sheets (1.1 g/cm^s). The dose distributions in the SRCTP (diameters of 6 cm [premature baby], 10 cm [neonates], and 14 cm [infants]) were evaluated. RFs were positioned every 5 mm along the radius at each SRCT-P, starting at center and ending on the surface. In this study, the absorbed dose and the dose distribution in the phantom were measured at 100 or 120 kV of the x-ray tube voltage. The other scanning parameters of the CT were 250 mA, 1.0 sec/rot, 1.25 x 8 mm slice thickness, and a 1.0 beam pitch. The mean center doses at 100 or 120 kV in 6, 10 and 14 cm of the SRCT-P were 37.0 or 64.2 mGy; 36.5 or 52.2 mGy; and 19.5 or 40.2 mGy, respectively. The mean surface doses in 100 or 120 kV at 6, 10 and 14 cm of the SRCTP were 33.9 or 57.9 mGy; 34.0 or 46.8 mGy; and 20.0 or 47.3 mGy, respectively. The absorbed dose was increased with a decrease in the phantom size. However, at 100 kV, the mean depth dose distributions at 6 or 10 cm of the SRCT-P were shown about the same value. The results indicated that the dose distribution in pediatric head CT becomes complex with patient head size and the tube voltage.