A randomized clinical trial comparing 50mCi and 100mCi of iodine-131 for ablation of differentiated thyroid cancers.

Objective: To compare the efficacy of low (50 mCi) and high dose (100 mCi) Iodine-131 in ablation of differentiated thyroid cancer remnants.

Methods: Baseline serum thyroglobulin (sTg), thyroglobulin antibody (Tg Ab) and diagnostic whole body iodine scan with 2 mCi of I-131 were performed in each individual. After 6 months serum Tg, Tg Ab (of-thyroxin) and WB iodine scan with 10 mCi of I-131 were done to assess the efficacy of the low and high dose of I-131. Iodine ablative therapy (IAT) was considered successful (complete ablation) if the I-131 whole body scan was negative and sTg level was undetectable. In case of positive scan and/or sTg level detectable the patient was considered as unsuccessfully/partially ablated.

Results: In group A, (high dose) successful IAT was seen in 12/20 (60%) patients. Of these 5/7 (71%) had follicular Carcinoma on histopathology and 7/13 (54%) had papillary Ca. In group B, (low dose) successful IAT was seen in 8/20 (40%) patients, out of which 3/10 (30%) had follicular Carcinoma on histopathology and had successful IAT. 5/10 (50%) patients with papillary Carcinoma had successful IAT. As far as histopathology is concerned, in group A, response to high dose I-131 was better in follicular type than papillary type. Whereas in group B, response to low dose I-131 was better in patients with papillary type than follicular.

Conclusion: 100 mCi of radioactive Iodine-131 (I-131) is a more effective therapeutic dose than 50 mCi (I-131) in the treatment of differentiated thyroid cancer remnants. Furthermore, follicular Carcinoma respond better to 100 mCi I-131 than 50 mCi while papillary Carcinoma showed an almost equal response to both.