Determination of Effective Half-Life of 131I 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 (http://www.ncrponline.org/)

NCRP Report # 39

NCRP Report # 124

NRC Regulatory Guide 8.39. (http://www.nrc.gov)

Teff (131I) = 0.8 x Tp

= 0.8 x 8.04 (d)

= 6.43 (d)

Exposure (E)

• Exposure (E) to person near patient

E= 34.6 x Г x Q0 x Tp x (1-e-0.693t/Tp)/ r2

Where: E= Accumulated exposure at time t in R34.6 = conversion factor of 24h/d x 1.44Г= Exposure rate constant ( 2.2 R x (cm2)/(mCi x h) at 1m Q0= Initial activity (mCi) at time of releaseTp= Physical half life of 131I (8.04 d)r= Distance from source (m) t= Exposure time (d)

NCRP Report No. 37

Dose (D)

D= 34.6ГQ0{E1Tp(0.8)(1-e-0.693(0.33)/Tp)+ e-0.693(0.33)/Tp E2F1T1eff + e-0.693(0.33)/Tp E2F2T2eff}/ (100cm)2

Where: D= Accumulated dose in RemF1 = Extrathyroidal uptake fraction ( 0.95)F2= Thyroid uptake fraction (0.05)E1= Occupancy Factor for the first 8 hours (0.25)E2= Occupancy factors from 8 h to total decay(0.25)T1eff = Tb1 x Tp/ Tb1 +Tp ( 0.32d)T2eff = Tb2 x Tp/ Tb2 +Tp (7.3d)

NCR 10 CFR 35.75c Appendix B Eq. 5

Objectives

• To determine the mean Teff of 131I based on the external exposure rates

• To determine the relationship and difference in Teff by gender & age groups

Materials & Methods

• 492 patients (345 F/147M); 1994-2006

• 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)

Determination of Teff (h), sample patient

y = 28.395e-0.0244x

R2 = 0.99910

5

10

15

20

25

30

0 10 20 30 40 50 60

Elapsed time (h)

Exp

osu

re r

ate

(mR

/h)

Teff = 0.693/0.0244= 28.4 h

Initial Activity= 205 mCi

Thyroid cancer

Demographic CharacteristicsFactor

Age (yr) 19-86Mean =48

Initial Activity (mCi) 69 -400Mean = 176.2

Initial Survey (mR/hr) 0.5-95Mean =24.2

Day 1 Survey (mR/hr) 0.1-35Mean =7

Day 2 Survey (mR/hr) 0.5-20Mean =2.8

20-29 30-39 40-49 50-59 60-69 70-7980-89

S1

0

5

10

15

20

25

Age Range (y)

Number of patients

No. of patients vs. Age Range (y)

20-29

30-39

40-49

50-59

60-69

70-79

80-89

Age of Interest

Age Vs. Effective half lifeMale

Age (y)

10 20 30 40 50 60 70 80

Effe

ctiv

e ha

lf lif

e (h

)

5

10

15

20

25

30

35

Col 5 vs Col 6

Age Vs. Effective half life

Age (y)

10 20 30 40 50 60 70 80 90

Effe

ctiv

e ha

lf lif

e (h

)

0

10

20

30

40

50

Col 8 vs Col 9

MaleN=19 r= 0.12

P=0.631

FemaleN= 61r=0.08

P= 0.559

Pearson Product Moment Correlation

Dose rates (mR/hr) at various times and at 1 meter after the administration of 131I for treatment of thyroid cancer

Time Post Administration (h)

0 24 48 72

NCRP Report No. 124 N=25 (per mCi) 0.216 0.109 0.067 0.018

LGH Database N=492 (per mCi) 0.14 0.04 0.01 NA

Comparison of the Teff in terms of age and sex differences

N Age Range (y) Sex (M/F) Teff (h) STDV (+/-)

Keating et al 11.4

Willegaignon J. et al 90 18-88 73/17 11.1 0.02David North et al 238 NA NA 14 NALGH Database 492 19-86 147/345 14.1

8.06

Independent t-Test, Parametric

Group Name N Mean Teff P Value = 0.188Female 111 14.22

Male 111 15.68

Mann-Whitney Rank Sum

Group N Median P Value =0.107Female 111 12.772

Male 111 13.667

Analysis of Variance (ANOVA)

Group Name N Mean (M) Mean (F)

Group I: 30-39 (y) 8 20.922 14.35

Group II: 40-49 (y) 8 13.579 8.73

Group III: 50-70 (y) 8 16.902 10.1

P Value 0.194 0.007

Bonferroni T-test

Comparison Mean Diff. P P<0.050

I vs. II 5.622 0.008 Yes

I vs. III 4.245 0.045 Yes

III vs. II 1.377 1.000 No

Discussions

• LGH Mean Teff (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 Teff between males and females

• Pearson test showed there is no correlation ( P>0.05) between Teff and patient’s age ANOVA Test revealed there is a possible statistical difference in mean Teff (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 Teff in terms of the thyroid mass, stage of diseases and Thyroid Stimulating Hormone (TSH) Level