European Union (1997) On Health Protection of Individuals against the Dangers of Ionizing Radiation to Medical Exposure. Council Directive 97/43/Euratom. Official Journal of the European Union No L 180, 22-27.
 EC (1999) Guidance on Diagnostic Reference Levels (DRLs) for Medical Exposures. Radiation Protection 109, Directorate-General, Environment, Nuclear Safety and Civil Protection, European Commission.
 Suliman, I.I., Abbas, N. and Habbani, F.I. (2007) Entrance Surface Doses to Patients Undergoing Selected Diagnostic X-Ray Examinations in Sudan. Radiation Protection Dosimetry, 123, 209-214.