Speaker
Dr
MIRELA ANGELA SAIZU
("Horia Hulubei" National Institute for Physics and Nuclear Engineering)
Description
The Whole Body Monitoring Laboratory from IFIN-HH, Magurele, Romania, performs, periodically, according to its Quality Assurance Programme, in vivo monitoring of the thyroid in order to be determined the I-131 retention by gamma spectrometry. The thyroid measurements are required, strictly, from radiation protection reasons, for people involved in nuclear medicine activities from hospitals and from radiopharmaceuticals production centres where there is a potential risk of occupational internal contamination with I-131 through inhalation.
The goal of the thyroid monitoring is to determine the amount of I-131 activity incorporated and to estimate the equivalent and effective doses. Reliable results suppose accurate radiation measurements which depend on the type of the in vivo thyroid monitoring system and on its correct calibration for the detection of the I-131 gamma energy lines. The retained activity in thyroid is quantified by processing the peak spectra of the main I-131 line of 364.5 keV.
The current thyroid spectrometer from IFIN-HH is based on a 2”x 2” NaI(Tl) scintillation detector that is traditionally used in gamma spectrometry for the detection of photons with energies higher than 50 keV. Despite its poor resolution, the NaI(Tl) detector was considered suitable for the detection of I-131 in thyroid because of its high detection efficiency and its room temperature operation mode.
Taking into account the developments on nuclear detectors based on inorganic scintillation materials, namely the Cerium-doped Lanthanum Bromide detector, manufactured by Saint-Gobain Crystals, it became challenging to test and evaluate this detector for in vivo thyroid monitoring, because of its attractive features as very good energy resolution, high gamma detection efficiency, very fast light output decay, operation at room temperature and detector small sizes.
A 1.5“ x 1.5” LaBr3(Ce) detector was available to replace the NaI(Tl) detector of the thyroid gamma spectrometer, in the same measurement geometry.
Background and radionuclide spectra were acquired in order to be evaluated its main characteristics for a qualitative and quantitative analysis, namely, the resolution, the efficiency and the Minimum Detectable Activity at the I-131 energy line of 364.5 keV.
There were performed the energy calibration using standard gamma etalon point sources and the efficiency calibration using a thyroid phantom and Monte Carlo simulation for calibration method validation.
Primary author
Dr
MIRELA ANGELA SAIZU
("Horia Hulubei" National Institute for Physics and Nuclear Engineering)
