Absorbed doses reduced by the use of rare-earth intensifying screens in rotational panoramic radiography with constant potential generator

Abstract

Absorbed doses modified by the use of rare-earth intensifying screens were measured with rotational panoramic radiography. Equipments with the constant potential, Veraview (J.Morita) and PM 2002 CC (Planmeca) was utilized. The optimum exposure settings at each tube voltage were determined by radiography of a Rando® phantom. Absorbed doses to parotid and thyroid glands were measured under the optimum exposure settings by using the Rando® phantom and thermoluminescence dosimeters. The sensitivity of the rare-earth intesifying screen system increased as the tube voltage bacame higher. Absorbed doses decreased steeply as the tube voltage became higher. The highly sensitive system of the LANEX REGULAR and T-Mat G (Eastman Kodak) reduced the thyroid gland dose to a half at 70 kV in comparison with the regular system of the PX-III (Kasei Optonics) and X-Omat S (Eastman Kodak). This high sensitivity, however, made it impossible to set the optimum tube current at above 70 kV. The another rare-earth system, the TRIMAX 16 and TRIMAX XUD (3M) had a lower sensitivity than the regular system of the PX-III and X-Omat S at below 80 kV. But they had equal sensitivity at the highest tube voltage of 80 kV.