Measurement in vivo of the cutaneous contamination provoked by a radioactive solution

The utilization of unsealed radioactive sources may cause cutaneous contamination accidents. The detriment is function of the dose of irradiation absorbed by the basal layer of the epidermis and mainly depends on the energy of the β rays, the molecular nature of contaminant and the time of contact with the skin. Furthermore, the penetration kinetic of a substance through the skin is influenced by different factors. So as to determine the dose of irradiation absorbed by the basal layer of the epidermis, we have realized different studies of cutaneous contamination in vivo in the pig: in a first study wa have compared cutaneous obsorption of a radioisotope (99mTC) diluted in physiological serum, in a aprotic solvent (DMSO) known to enhance the cutaneous permeability, and by varying the pH of the solution. In a second part, we have compared the cutaneous absorption after contamination times of 1 and 5 minutes, and in different hydration states of the skin before contamination. Results of the in vivo cutaneous absorption, for contaminating times of 1 and 5 minutes, have shown a loss of 5 % of external counting of the electrons (external counting of the 120 KeV electron of 99mTc), one hour after the contamination, for all the chemical vectors. The variation of the contamination time and the state of hydration of the skin before contamination showed similar results. From these experimental results, an exponential distribution model of the radioisotope in the skin has allowed to calculate the dose rate equivalent of irradiation absorbed by the basal layer of the ipidermis: during a contamination of 5 minutes on a surface of 9 cm2 with 99mTc, this dose rate equivalent was 0.98 mSv h-1 by 37 kBq cm-2 (μCi cm-2). By the Monte-Carlo method in the hypothesis where there is no cutaneous absorption, it was 0.94 mSv h-1 by 37 kBq cm-2. A preliminary experience with a β emitter (14C) has confirmed a less of 5% of the counting in the same experimental conditions. (author). 25 refs., 7 tabs., 4 curves