Radiation Dose-rate Reduction Pattern in Well-differentiated Thyroid Cancer Treated with I-131.

ABSTRACT

OBJECTIVE: To determine the patterns of dose rate reduction in single and multiple radioiodine (I-131) therapies in cases of well differentiated thyroid cancer patients. STUDY DESIGN: Analytical series. PLACE AND DURATION OF STUDY Department of Nuclear Medicine and Radiation Physics, Multan Institute of Nuclear Medicine and Radiotherapy (MINAR), Multan, Pakistan, from December 2006 to December 2013. METHODOLOGY: Ninety three patients (167 therapies) with well differentiated thyroid cancer treated with different doses of I-131 as an in-patient were inducted. Fifty four patients were given only single I-131 therapy dose ranging from 70 mCi (2590 MBq) to 150 mCi (5550 MBq). Thirty nine patients were treated with multiple I-131 radioisotope therapy doses ranging from 80 mCi (2960 MBq) to 250 mCi (9250 MBq). T-test was applied on the sample data showed statistically significant difference between the two groups with p-value (p < 0.01) less than 0.05 taken as significant. RESULTS: There were 68 females and 25 males with an age range of 15 to 80 years. Mean age of the patients were 36 years. Among the 93 cases of first time Radio Active Iodine (RAI) therapy, 59 cases (63%) were discharged after 48 hours. Among 39 patients who received RAI therapy second time or more, most were discharged earlier after achieving acceptable discharge dose rate i.e 25 µSv/hour; 2 out of 39 (5%) were discharged after 48 hours. In 58% patients, given single I-131 therapy dose, majority of these were discharged after 48 hours without any major complications. CONCLUSION: For well differentiated thyroid cancer patients, rapid dose rate reduction is seen in patients receiving second or subsequent radioiodine (RAI) therapy, as compared to first time receiving RAI therapy.