Effective Half-life of I-131 in Patients with Differentiated Thyroid Cancer Treated by Radioactive I-131

Park, Seok Gun

Abstract

PURPOSE: Effective half life of I-131 (T(eff)) in patients with differentiated thyroid cancer treated by I-131 is must-know value for dose calculation and determination of release time from isolation room. There has been no report about T(eff) in Koreans. Thus, author tried to measure dose rate without radiation exposure to faculty members and calculated T(eff).
METHODS
Probe of radiation survey meter was fixed at the wall of isolation room, and body of survey meter was placed outside the room. With this simple arrangement, author could measure radiation frequently without radiation exposure to faculty members in 68 patient (F=55, M=13, age=47+/-13.7) treated by I-131 (3.7~7.4 GBq) for differentiated thyroid cancer from Jan 2006 to Dec 2006. From this data, T(eff), 48 hr retention rate, and the time necessary to whole body retention of I-131 become less than 1.1 GBq were calculated. Serum creatinine levels were measured before and after thyroid hormone withdrawal.
RESULTS
T(eff) was 15.4+/-4.3 hr (9.4~32.5 hr). There was a loose correlation between T(eff) and serum creatinine concentration (r=0.45). 48hr retention was 4.9+/-4.2% (1~23%). Time necessary to whole body retention of I-131 become less than 1.1 GBq was calculated as 47.1+/-13.2 hr for 9.25 GBq, 42.1+/-11.9 hr for 7.4 GBq, 35.7+/-10.0 hr for 5.55 GBq, and 26.7+/-7.5 hr for 3.7 GBq dose of I-131.
CONCLUSION
Author successfully measured radiation dose rates in isolated patients treated by high dose of I-131 without radiation exposure to the faculty members with simple arrangement of survey meter probe. Using those data, T(eff) and some other indices were calculated.