Determination of Effective Half-Life of 131 I in Thyroid Cancer Patients Hoang T. Vu Allen Hrejsa & Alex Markovic *Department of Medical Radiation Physics, Rosalind Franklin University of Medicine and Sciences, North Chicago, IL & Department of Medical Physics, Advocate Lutheran General Hospital Park Ridge, IL

Historical Background NCRP Report # 37 ( NCRP Report # 39 NCRP Report # 124 NRC Regulatory Guide ( T eff ( 131 I) = 0.8 x T p = 0.8 x 8.04 (d) = 6.43 (d)

Exposure (E) Exposure (E) to person near patient E= 34.6 x Г x Q 0 x T p x (1-e t/Tp )/ r 2 Where:E= Accumulated exposure at time t in R 34.6 = conversion factor of 24h/d x 1.44 Г= Exposure rate constant ( 2.2 R x (cm 2 )/(mCi x h) at 1m Q 0 = Initial activity (mCi) at time of release T p = Physical half life of 131 I (8.04 d) r= Distance from source (m) t= Exposure time (d) NCRP Report No. 37

Dose (D) D = 34.6ГQ 0 {E 1 T p (0.8)(1-e (0.33)/Tp) + e (0.33)/Tp E 2 F 1 T 1eff + e (0.33)/Tp E 2 F 2 T 2eff }/ (100cm) 2 Where:D= Accumulated dose in Rem F 1 = Extrathyroidal uptake fraction ( 0.95) F 2 = Thyroid uptake fraction (0.05) E 1 = Occupancy Factor for the first 8 hours (0.25) E 2 = Occupancy factors from 8 h to total decay(0.25) T 1eff = T b1 x T p / T b1 +T p ( 0.32d) T 2eff = T b2 x T p / T b2 +T p (7.3d) NCR 10 CFR 35.75c Appendix B Eq. 5

Objectives To determine the mean T eff of 131 I based on the external exposure rates To determine the relationship and difference in T eff by gender & age groups

Materials & Methods 492 patients (345 F/147M); Exposure rates (E.R.) were measured at t=0, 24, 48 h at 1m Min. stay= 1d, Majority=2 d, Statistical analysis: t-test, Pearson, Man- Whitney Rank Sum, ANOVA (SigmaStat 3.1)

Results Activity = 205 mCi (7.59 GBq) T eff = 0.693/0.0244= 28.4 h Initial Activity= 205 mCi Thyroid cancer

Demographic Characteristics Factor Age (yr) Mean =48 Initial Activity (mCi) Mean = Initial Survey (mR/hr) Mean =24.2 Day 1 Survey (mR/hr) Mean =7 Day 2 Survey (mR/hr) Mean =2.8

Age of Interest

Male N=19 r= 0.12 P=0.631 Female N= 61 r=0.08 P= Pearson Product Moment Correlation

Dose rates (mR/hr) at various times and at 1 meter after the administration of 131 I for treatment of thyroid cancer Time Post Administration (h) NCRP Report No. 124 N=25 (per mCi) LGH Database N=492 (per mCi) NA

Comparison of the T eff in terms of age and sex differences N Age Range (y) Sex (M/F) T eff (h) STDV (+/-) Keating et al 11.4 Willegaignon J. et al / David North et al238NA NA 14 NA LGH Database /

Independent t-Test, Parametric Group Name N Mean T eff P Value = Female Male Mann-Whitney Rank Sum GroupN Median P Value =0.107 Female Male

Analysis of Variance (ANOVA) Group Name N Mean (M)Mean (F) Group I: (y) Group II: (y) Group III: (y) P Value Bonferroni T-test ComparisonMean Diff.P P<0.050 I vs. II Yes I vs. III Yes III vs. II No

Discussions LGH Mean T eff (14.16 h) agrees with one group’s data but longer than two others’ data. Independent t-test revealed there is no statistical difference in T eff between males and females Pearson test showed there is no correlation ( P>0.05) between T eff and patient’s age ANOVA Test revealed there is a possible statistical difference in mean T eff (F-age groups), limitation = small N Bonferroni Test determined that the difference lies between age groups I vs. II & I vs. III Useful instructions for releasing of patients A more accurate dose to general public

Future Research To determine if there is a difference in mean T eff in terms of the thyroid mass, stage of diseases and Thyroid Stimulating Hormone (TSH) Level