A methodology for auto-monitoring of internal contamination by 131I in nuclear medicine workers.

The manipulation of 131I in Nuclear Medicine involves significant risks of internal contamination of the staff. In the event of an accidental contamination, or when the Radiological Protection Program includes routine individual monitoring of internal contamination, it is necessary to implement internal dose estimation through in vivo and in vitro bioassay techniques. Due to the huge extension of the Brazilian country, this type of monitoring becomes unfeasible if all measurements have to be performed at the institutes of the CNEN. Thus, if the Nuclear Medicine Centres (NMC) become able to conduct the monitoring of their employees, this skill would be of great significance. The methodology proposed in this work consists in a simple and inexpensive protocol for auto-monitoring the internal contamination by 131I, using the resources available at the NMC. In order to verify the influence of the phantom in the calibration factor for the measurement of 131I in thyroid, it was performed a comparison among a variety of phantoms commercially available, including the Neck-Thyroid Phantom developed in IRD. A protocol for performing in vivo and in vitro measurements by the NMC was established. The applicability of the individual monitoring techniques was also evaluated by comparing the detection limits with the derived limits associated with the annual dose limits for workers.