title: Counting efficiency of whole-body monitoring system using BOMAB and ANSI/IAEA thyroid phantom due to internal contamination of 131I.
abstract: In this study, the effect of Indian reference BOttle MAnnikin aBsorber (BOMAB) neck with axial cavity and American National Standards Institute (ANSI)/International Atomic Energy Agency (IAEA) thyroid phantom using pencil sources of (133)Ba ((131)I simulant) on counting efficiency (CE) is seen experimentally in static geometry for whole-body monitoring system comprising 10.16-cm diameter and 7.62-cm-thick NaI(Tl) detector. The CE estimated using the neck part of BOMAB phantom is 50.2% lower in comparison with ANSI phantom. In rest of the studies FLUKA code is used for Monte Carlo simulations using ANSI/IAEA thyroid phantom. The simulation results are validated in static geometries with experimental CE and the differences are within 1.3%. It is observed that CE for pencil source distribution is 3.97% higher for (133)Ba in comparison with CE of (131)I source. Simulated CE for pencil source distribution is 4.7% lower in comparison with uniform source distribution in the volume of thyroid for (131)I. Since the radiation workers are of different physique; overlying tissue thickness (OTT) and neck-to-detector distance play an important role in the calculation of activity in thyroid. The CE decreases with increase in OTT and is found to be 5.5% lower if OTT is changed from 1.1 to 2 cm. Finally, the simulations are carried out to estimate the variation in CE due to variation in the neck-to-detector distance. The CE is 6.2% higher if the neck surface-to-detector distance is decreased from 21.4 to 20.4 cm and it goes on increasing up to 61.9% if the distance is decreased to 15.4 cm. In conclusion, the calibration of whole-body monitoring system for (131)I should be carried out with ANSI/IAEA thyroid phantom, the neck-to-detector distance controlled or the CE corrected for this, and the CE should be corrected for OTT.
authors.affiliation: Internal Dosimetry Section, Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai 400085, India vandanan@barc.gov.in.
authors.forename: V P
authors.initials: VP
authors.lastname: Ghare
authors.affiliation: Internal Dosimetry Section, Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
authors.forename: H K
authors.initials: HK
authors.lastname: Patni
authors.affiliation: Internal Dosimetry Section, Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
authors.forename: D K
authors.initials: DK
authors.lastname: Akar
authors.affiliation: Internal Dosimetry Section, Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
authors.forename: D D
authors.initials: DD
authors.lastname: Rao
mesh_terms: D002138:Calibration; D003198:Computer Simulation; D006801:Humans; D007390:International Agencies; D007457:Iodine Radioisotopes / Q000032:analysis*; D008348:Manikins; D009010:Monte Carlo Method; D009333:Neck / Q000033:anatomy & histology / Q000528:radiation effects; D009678:Nuclear Energy; D019047:Phantoms, Imaging; D011834:Radiation Monitoring / Q000295:instrumentation / Q000379:methods*; D013961:Thyroid Gland / Q000033:anatomy & histology* / Q000528:radiation effects*; D014915:Whole-Body Counting / Q000295:instrumentation / Q000379:methods*
chemical_list: D007457:Iodine Radioisotopes