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Determination of age specific ¹³¹I S-factor values for thyroid using anthropomorphic phantom in Geant4 simulations
Ziaur Rahman1, Syed Bilal Ahmad2, Sikander M Mirza2
1Health Physics Division, Pakistan Institute of Nuclear Science & Technology, Nilore, Islamabad 45650, Pakistan.
Abstract:
Using anthropomorphic phantom in Geant4, determination of β- and γ-absorbed fractions and energy absorbed per event due to (131)I activity in thyroid of individuals of various age groups and geometrical models, have been carried out. In the case of (131)I β-particles, the values of the absorbed fraction increased from 0.88 to 0.97 with fetus age. The maximum difference in absorbed energy per decay for soft tissue and water is 7.2% for γ-rays and 0.4% for β-particles. The new mathematical MIRD embedded in Geant4 (MEG) and two-lobe ellipsoidal models developed in this work have 4.3% and 2.9% lower value of S-factor as compared with the ORNL data.
