Beyond iodine-131: protective effect of stable iodine for all iodine isotopes of radiological concern.

Abstract

Administering stable iodine is an effective strategy to protect the thyroid in case of an accidental release of radioiodines.¹³¹I is the most concerning iodine isotope due to its amount in the reactor vessel and its relatively long half-life. These factors result in¹³¹I dominance in the total thyroid dose, and many studies focus on this isotope. The protective effect (PE) of stable iodine for other iodine isotopes is not well documented, and this study examines¹³²I and nine other isotopes with longer half-lives. The predicted trend in PE is estimated using a biokinetic toy model of the blocking effect. Then, the Zanzonico and Beckermodel (2000Health Phys.78660-7) is implemented for the inhalation of aerosol type F with an AMAD of 1μm. The PE for administration of 130 mg KI is tabulated for administration time between 96 h prior to the intake and 48 h after the intake for 10 isotopes including¹³¹I. It has been found that, regardless of the timing of stable iodine administration, the PE is similar for¹²⁴I (T_1/2∼ 4.2 d),¹³¹I (T_1/2∼ 8 d), and other isotopes with longer half-lives. For isotopes with shorter half-lives, the relative PE (normalised to the respective¹³¹I values) depends on the timing of stable iodine administration and the isotopes' half-life. If stable iodine is taken after intake, the shorter the half-life the lower the PE. If stable iodine is taken before intake the opposite applies. For stable iodine administration 48 h before the intake the PE is 93% for¹³²I and 73% for¹³¹I, for administration 24 h before the intake these values are 99 and 95%. Taken 6 h after the intake the PE is only 9% for¹³²I but still 51% for¹³¹I. The results obtained here could be considered for emergency planning and preparedness as well as communication with the public in case of accidental radioiodine release.