Absorbed dose

Abstract: The objective of this paper is to present a new type of volumetric CT which uses the cone-beam technique instead of traditional fan-beam technique. The machine is dedicated to the dento-maxillo-facial imaging, particularly for planning in the field of implantology. The main characteristics of the unit are presented with reference to the technical parameters as well as the software performance. Images obtained are reported as various 2D sections of a volume reconstruction. Also, measurements of the geometric accuracy and the radiation dose absorbed by the patient are obtained using specific phantoms. Absorbed dose is compared with that given off by spiral CT. Geometric accuracy, evaluated with reference to various reconstruction modalities and different spatial orientations, is 0.8–1 % for width measurements and 2.2 % for height measurements. Radiation dose absorbed during the scan shows different profiles in central and peripheral axes. As regards the maximum value of the central profile, dose from the new unit is approximately one sixth that of traditional spiral CT. The new system appears to be very promising in dento-maxillo-facial imaging and, due to the good ratio between performance and low cost, together with low radiation dose, very interesting in view of large-scale use of the CT technique in such diagnostic applications.

Abstract: A protocol is given to provide radiological physicists with an accurate means of measuring radiation doses on phantoms. Plastics, as well as water, are considered as phantoms. A new quantity, the cavity‐gas calibration factor, is introduced.(AIP)

Abstract: PREFACE MAIN POINTS EXECUTIVE SUMMARY 1. INTRODUCTION 2. Quantities used in radiation protection for external exposure 3. Determination of organ absorbed doses OF the ICRP/ICRU REFERENCE phantomS 4. Conversion coefficients for external exposure 5. Relationships between dose conversion coefficients For operational and protection quantities References Annex A - Effective dose conversion coefficients Annex B - Organ absorbed dose conversion coefficients for photons Annex C - Organ absorbed dose conversion coefficients for neutrons Annex D - Skeletal fluence-to-dose response functions - Photons Annex E - Skeletal fluence-to-dose response functions - Neutrons Annex F - Conversion coefficients for the eye lens Annex G - Special considerations for assessing the local skin equivalent dose Annex H - Effective dose for superior hemisphere semi isotropic irradiation for aircraft crew dosimetry Annex I - Methods used for evaluation of reference data