Annual patient effective dose equivalent can be considered as a quantitative physical parameter describing the activities performed in each nuclear medicine department. Annual staff dose equivalent could be also considered as a parameter describing the amount of radiation risk for performing the activities. We calculated the staff to patient dose equivalent ratio to be used as a physical parameter for quantification of ALARA law in nuclear medicine departments. Materials and Methods: As a part

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... f nationwide study, this paper reports the staff and patient absorbed dose equivalents from diagnostic nuclear medicine examinations performed in four nuclear medicine departments during 1999-2002. The type and frequency of examinations in each department were determined directly from hospital medical reports. Staff absorbed dose equivalents were calculated from regular personal dosimeter reports. Results: The total number of examinations increased by 16.7% during these years. Annual patient collective dose equivalent (EDE) increased about 13.0% and the mean effective dose equivalent per exam was 3.61±0.07 mSv. Annual total staff absorbed dose equivalent (total of 24 radiation workers) in four departments increased from 40.45 mSv to 47.81 mSv during four years that indicates an increase of about 20.6%. The average of annual ratios of staff to patient effective dose equivalents in four departments were 1.83×10 -3 , 1.04×10 -3 , 3.28×10 -3 and 3.24×10 -3 , respectively, within a range of 0.9×10 -3 -4.17×10 -3 . The mean value of ratios in four years was about 2.24×10 -3 ± 1.09×10 -3 that indicates the staff dose of about two 1000th of patient dose. Conclusion: The mean value of ratios in four years was about 1.89×10 -3 ± 0.95×10 -3 indicating the staff dose of about one 1000th of the patient dose. The staff to patient absorbed dose equivalent ratio could be used as a quantitative parameter for describing ALARA law in radiation protection and risk-benefit assessments. Iran. J. Radiat. Res., 2004; 2 (2): 63-68 Keywords: Diagnostic nuclear medicine, staff and patient effective dose equivalent.