Health Physics Vol. 58. No.4 (April). pp. 399-403. 1990 Printed in the U.S.A. • Paper BETA AND ELECTRON DOSE CALCULATIONS TO SKIN DUE TO CONTAMINATION BY COMMON NUCLEAR MEDICINE RADIONUCLIDES E. L. McGuire and G. V. Dalrymple John L. McClellan Memorial Veterans Hospital and University of Arkansas for Medical Sciences, Little Rock, AR 72205 0017-9078/90 $3.00 +.00 © 1990 Health Physics Society Pergamon Press pic (Received 19 June 1989; accepted 30 October 1989) Abstract- We present dose calculations to the basal cell layer of the epidermis resulting from skin contamination by radionuclides used in nuclear medicine. Dose calculations were made using the computer code VARSKIN, as modified by us to include these radionuclides and to account for tbeir monoenergetic electron emissions. indicate tbat basal skin doses (taken to be at a depth of 0.007 cm) are approximately 1 cGy b -I per 3.7 X 10- 4 Bq cm- 2 (l rad b -I per #Ci cm -2) from 99mTc, 111In and 201TI, implying tbat establisbed limits may be approached under certain circumstances. The implication of these results for small areas of contamination is also discussed. INTRODucnON THE DOSE to extremities of workers in nuclear medicine is commonly recognized to be of concern, since technol- ogists typically handle syringes containing 37 MBq (mCi) quantities of photon emitters for injection into patients. In addition, elutions from 99Moj 99m Tc generators con- taining 3.7 X 10 10 Bq ( 1 Ci) or more of 99mTc are some- times handled. Thus, a small dosimeter is normally worn on one of the fingers to assess the external dose. However, standard monitoring methods are not suitable for deter- mining the dose to the basal cell layer of the epidermis due to contamination directly on the skin. Considerable concern has been raised recently over the dose aspects of a ,B-emitting "hot particle" on the skin of nuclear power plant workers (USNRC 1987; Chabot and Skrable 1988). Because very large localized doses can be calculated from ,B emitters or electrons, the implication and relevance of these doses has been studied by NCRP Scientific Committee 80-1 (NCRP 1988). In nuclear medicine, skin contamination occurs that is localized but more extensive than that addressed by SC 80-1. In this paper, we review the dose calculation principles from ,B and electron emitters applied to the nuclear medicine set- ting. MATERIALS AND METHODS Description of events We recently had occasion to evaluate the dose to two nuclear medicine technologists who were contaminated by 201Tl chloride and 99mTc pertechnetate in separate in- cidents. In the case of the 20lTl contamination, the tech- 399 nologist was not wearing gloves (at variance with estab- lished technique), his rationale being that he was not in contact with body fluids directly because it was a flush dose and thus did not require gloves. Because of a faulty connection of the syringe to the infusion line, approxi- mately 3.7 X 10 7 Bq (I mCi) 20ITI was leaked, a large amount that contaminated both hands of the technologist. After cleansing efforts were exhausted, an estimated 18.5 X 10 4 Bq (5 /-lCi) remained on both hands. This was determined with a 2.54 cm X 2.54 cm (I "x 1") NaI (Tl) area monitor, in which a count rate of 25 kcts min -I at - 8 cm was registered. In the second incident, a technologist was preparing a cylindrical test phantom in which 370 MBq (10 mCi) of 99mTc was injected in the phantom and mixed. The technologist was wearing gloves but nevertheless noted a count rate significantly in excess of background on her hands after she had completed the preparation process and removed her gloves. The contamination was discov- ered using an NaI(Tl) area monitor which is routinely used to monitor low-level contamination. A certain brand of gloves has been suspected by us of having pinhole leaks, causing this contaminating event. To localize the areas of contamination, as well as to more precisely quantitate the activity on their hands to facilitate dose calculations, a 5-min computer image in a 128 X 128 matrix was acquired on a scintillation camera with a LEAP collimator.* Counts were acquired at 20% energy windows centered on the principal photopeaks (75 keVand 167 keY for 201Tl and 140 keY for 99mTc). The .. 400 AfT Scintillation Camera and Star Computer, GE Medical Systems, Milwaukee, WI 53201.