Air Monitoring to Control the Intake of Airborne Radioiodine-131 Contaminants by Nuclear Medicine Workers

Inhalation of radioiodine-131 is the largest cause of internal dose to nuclear medicine workers. The concentration of radioiodine-131 in air is limited by the Derived Air Concentration (DAC) of 416.67 Bq/m3. In this study air monitoring shall be performed to measure the radioiodine-131 contaminant in air by sample collection and analysis. Air samples were drawn from areas where there is a potential for I-131 airborne radioactivity e.g. in the hot laboratory, radioiodine treatment rooms, radioactive waste collection areas and waste water treatment plant. A portable battery-operated air sampler, Gilian BDX II with carbon- impregnated cellulose filters was used for air sampling. The flow rate was adjusted to 3 liters per minute and the sampler run for 180 minutes. Iodine-131 radioactivity on filter was measured for 10 minutes by 2 NaI(Tl) gamma counters, Perkin Elmer Wallac Wizard 1480 (3''x3'') and Atomlab 950 PC (2''x2'') with and objective for inter comparison. Counting efficiency of the counters are 57 and 39 percent respectively. Agreeable results of I-131 radioactivity were obtained from both gamma counters. The mean I-131 concentrations measured by Wallac(Atomlab) were 31.59±16.31 (29.84±14.74) Bq/m3 in radioiodine fume hood for treatment dose dispensing, 8.98±4.33 (7.58±5.10) Bq/m3 in fume hood accommodated with a dose calibrator, 7.80±5.39 (7.54±5.04) Bq/m3 in radioactive waste storage area, 0.03±0.54 (0.03±0.57) Bq/m3 in patient waiting area, 2.94±3.60 (2.55±2.98) Bq/m3 in hospital ward waste collection area and 0.03±0.01 (0.03±0.01) Bq/m3 in the water treatment plant area. Radioiodine concentrations in patient's room increases linearly as the administered dose was increasing. Mean±SD of the measured concentrations were 11.63±9.30 (9.86±8.98) Bq/m3, 18.57±13.24 (17.35±12.33) Bq/m3 and 31.90±22.32 (30.90±22.49) Bq/m3 for the administered doses of 3.7, 5.55 and 7.4 Bq respectively. Radioiodine concentrations in all specified areas were less than the DAC of 416.67 Bq/m3 assigned for I-131. This demonstrated that the work place condition is satisfactory and the level of protection provided to the worker is sufficient to minimize the internal dose equivalent. The inhalation of radioiodine vapors is the important routes of entry of radioiodine into the human body. The level of airborne I-131 radioactivity should be maintained well below allowable levels to keep the internal dose equivalent contribution to the total effective dose equivalent small. (author)