ABSORBED DOSE IN THE SKIN FROM BETA-EMITTERS IN MEDICAL AND LABORATORY CONTAINERS

The International Commission on Radiation Protection have recently rec ommended an annual dose limit for the skin of radiation workers of 500 mSv at a depth of 20-100 mu m averaged over any 1 cm(2) regardless of the area exposed. It has previously been shown by the authors that be ta dose rates on the outer surfaces of typical laboratory containers ( vials, test tubes) or on medical syringes can exceed 100 mSv h(-1) for radionuclide concentrations of the order of 1 MBq g(-1), depending on container diameter, wall thickness and material and the beta particle energy spectrum. Since the fingers are frequently in contact with suc h containers it is of some importance to extend these dose calculation s to depths below the skin surface, taking into consideration the anat omy of skin on the fingers. Using an extension of a Monte Carlo method previously described, dose rates have been calculated for the clinica lly useful radionuclides Y-90, P-32, Au-198, Sm-153 and I-131. For pol ypropylene syringes the beta dose rates at a depth of 270 mu m (a typi cal basal cell depth in the fingers) range from 77 to 135 mGy h(-1) pe r MBq g(-1) for Y-90 (maximum energy 2.27 MeV) and approximately zero to 0.62 mGy h(-1) per MBq g(-1) for I-131 (maximum energy 0.61 MeV). T hese results emphasize the importance of adequate finger protection wh en using high energy beta emitters and especially for clinicians who t ypically inject specific activities of the order of 100 MBq g(-1) of P -32; in such cases annual permissible dose rates are exceeded in a mat ter of minutes. It is recommended that a minimum of 5 mm perspex finge r protection be used for Y-90 and P-32.