Absorbed dose in the skin from beta emitters in medical and laboratory containers

The International Commission on Radiation Protection have recently recommended an annual dose limit for the skin of radiation workers of 500 mSv at a depth of 20-100 microns averaged over any 1 cm2 regardless of the area exposed. It has previously been shown by the authors that beta 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 such containers it is of some importance to extend these dose calculations to depths below the skin surface, taking into consideration the anatomy of skin on the fingers. Using an extension of a Monte Carlo method previously described, dose rates have been calculated for the clinically useful radionuclides 90Y, 32P, 198Au, 153Sm and 131I. For polypropylene syringes the beta dose rates at a depth of 270 microns (a typical basal cell depth in the fingers) range from 77 to 135 mGy h-1 per MBq g-1 for 90Y (maximum energy 2.27 MeV) and approximately zero to 0.62 mGy h-1 per MBq g-1 for 131I (maximum energy 0.61 MeV). These results emphasize the importance of adequate finger protection when using high energy beta emitters and especially for clinicians who typically inject specific activities of the order of 100 MBq g-1 of 32P; in such cases annual permissible dose rates are exceeded in a matter of minutes. It is recommended that a minimum of 5 mm perspex finger protection be used for 90Y and 32P.