Kunihiro Nakada, Abstract Co-Author: Nothing to Disclose

Mika Tamura BS, Presenter: Nothing to Disclose

Yasushi Satoh BS, Abstract Co-Author: Nothing to Disclose

Ysushi Furuta MD, PhD, Abstract Co-Author: Nothing to Disclose

Hiroki Sugie MD, Abstract Co-Author: Nothing to Disclose

Masayuki Sakurai, Abstract Co-Author: Nothing to Disclose

Low iodine diet (LID) is an important preparation for radioiodine I-131 therapy for differentiated thyroid cancer. However, practice of LID for longer period is not easy for residents in iodine sufficient district. The aim of the study was to determine efficacy of a one-week LID program on total body iodine and radioiodine uptake in the remnant tissue after total thyroidectomy.

Twenty-seven Japanese patients with post surgical papillary thyroid cancer were enrolled. All patients underwent total thyroidectomy by a single surgical team at a single tertiary center. Surgical finding of primary tumor was either pT3 or pT4a. Radioiodine ablation was done with 30mCi of I-131 under rhTSH injection for 2days. Replacement of L-T4 was not discontinued. The average of serum TSH levels (μU/ml) in patients at the day of ablation were 158±43. After instruction by a dietitian, LID (< 100μg/day) was done from 7 days before to 2 days after I-131 administration. As a parameter for total body iodine, urinary iodine concentration corrected by urinary creatinine (UIC) was measured before start of LID and at the day of ablation therapy. Radioiodine uptake in the remnant tissue (RU;%) was determined at 3 days after I-131 ingestion using gamma camera. Relationship between UIC and RU was evaluated.

UIE levels(μg/gCre) in patients before LID varied widely (25-7800). After LID for 7 days, mean value of UIE levels were decreased to 9% of the baseline value (52 vs.568, p<0.01). RU ranged from 0.3 - 11.1. There was a significant inverse correlation between UIE at the day of I-131 therapy and RU(r=-0.70, p<0.01). Patients with lower UIE (<100) at I-131 ingestion had higher RU than those with higher LIU (5.1 vs. 2.8. p<0.01). Hyponatremia was not developed in any of the patients.

A one-week LID successfully decreased total body iodine in patients with post surgical thyroid cancer without causing any significant side-effects. Moreover, low UIE enhanced I-131 uptake in the remnant tissue. A one-week LID may be simple and valuable in rhTSH-aided ablation for thyroid cancer.

In patients undergoing rhTSH-aided ablation without stopping l-T4 replacement, low iodine diet for just 1 week may be as efficient as that for 2 to 3 weeks in enhancing I-131 uptake.

Nakada, K, Tamura, M, Satoh, Y, Furuta, Y, Sugie, H, Sakurai, M, Efficacy of a One-week Stringent Low Iodine Diet for Decreasing Urinary Iodine Concentration and Enhancing I-131 Uptake in rhTSH-aided Radioiodine Ablation for Papillary Thyroid Cancer.  Radiological Society of North America 2013 Scientific Assembly and Annual Meeting, December 1 - December 6, 2013 ,Chicago IL. http://archive.rsna.org/2013/13025199.html