Evaluation of internal occupational exposure by 123I in a radiopharmaceutical production facility

• In vivo and in vitro bioassay methods have been optimized for monitoring of 123I.
• Methods are sufficiently sensitive to detect 123I at the registry level of 1 mSv.
• The critical group is composed by workers from quality control of mIBG.
• Internal monitoring of the critical group should be performed weekly.
• In vitro bioassay should be carried out as a routine basis and in non-usual events.

123I is a photon emitter radionuclide (159 keV) used for diagnostic procedures of endocrinal diseases in nuclear medicine. Since 1998 it is produced at the industrial radiopharmaceutical plant operated by the Institute for Nuclear Energy (IEN-CNEN) and supplied to clinics located in the State of Rio de Janeiro, in Brazil. The production of this radionuclide represents a risk of internal occupational exposure. According to international recommendations, workers involved in this activity should be routinely monitored in order to comply with dose limits and keep individual exposures as low and reasonably achievable. The Radiation Protection Plan implemented at the IEN includes annual in vivo measurements of 123I in the thyroid performed at the In Vivo Monitoring Laboratory of the Institute for Radiation Protection and Dosimetry (IRD-CNEN). This work describes a series of improvements on the measurement techniques used for the monitoring of the workers from the facility, including (i) optimization of in vivo measurement of the thyroid using an array of high-purity germanium detectors, (ii) development of a new in vitro bioassay method for the determination of 123I in urine samples using a HPGe germanium detector and (iii) the establishment of a methodology for internal dose assessment, based on bioassay data. The sensitivity of the methods allow detection of 123I activities below derived registry level of 1 mSv for the incorporation scenarios of exposure assumed in this work. Thus, it can be concluded that the methods are suitable for application in routine monitoring of workers occupationally exposed to 123I in this facility.