Assessment of Activity Concentration and Effective Doses from Bioassay Sample of Occupational Workers in NINMAS, Bangladesh

Unsealed radioactive sources such as 131I and 99mTc are used in Nuclear Medicine Centers, to diagnose and treat patients, pose significant risks of internal exposure to the occupational workers. 131I is highly volatile and radiotoxic, which may pose an occupational radiological hazard, especially in places where significant activities are routinely handled. In such situations, worker handling unsealed sources of 131I may be internally exposed by inhalation. Though 99mTc is not as volatile, however it is the most widely used imaging agents in nuclear medicine. Moreover, due to short half life the internal radiation risk that it poses may sometimes be over looked. Although it is recognized that in nuclear medicine centers external exposure is usually higher than internal exposure, the risks associated with intakes should be estimated in each case and, if necessary, staff involved in the handling of unsealed sources should be routinely monitored in order to ensure that individual doses are kept as low as possible [1]. Internal monitoring should also be performed in response to an accident or suspected inhalation or ingestion intake. 131I is a short-lived radionuclide (half-life; 8 days). It decays by beta emission producing photons of 0.36 MeV. For adults, it is assumed that, of the iodine reaching the blood, 30% is transported to the thyroid gland and other 70% is excreted directly in urine via the urinary bladder. The biological half-life in blood is taken to be 6 h. Iodine incorporated into thyroid hormones leaves the gland with biological half-life of 12 days. Most iodine (80%) is subsequently released and is available in the circulation for uptake by the thyroid or direct urinary excretion; the remainder is excreted via the large intestine in the faeces. Because of the short physical half-life of 131I, this recycling is not important in terms of the committed effective dose. Iodine is rapidly absorbed into the circulation following inhalation or ingestion. It is concentrated in the thyroid and excreted predominantly via urine [2]. There are 17 Nuclear Medicine Centers in Bangladesh, from these Centers only one is selected for this study: National Institute of Nuclear Medicine and Allied Science (NINMAS) Dhaka. While processing and labeling of the liquid sources with labeling compounds, the sources may enter the bodies of the occupational worker through inhalation and ingestion. The present work was taken up to measure the contamination of the occupational staff because of the above radiopharmaceuticals.