Low iodine diet of four days is sufficient preparation for 131I therapy in differentiated thyroid cancer patients.

CONTEXT No consensus exists about the optimal duration of the low iodine diet (LID) in preparation of 131I therapy in differentiated thyroid cancer (DTC) patients. OBJECTIVE This work aimed to investigate if a LID of four days is enough to achieve adequate iodine depletion in preparation for 131I therapy. In addition, the nutritional status of the LID was evaluated. METHODS In this prospective study, 65 DTC patients treated in two University Medical Centers were included between 2018 and 2021. The patients collected 24-h urine on day four and seven of the LID and kept a food diary before and during the LID. The primary outcome was the difference between the 24-h urinary iodine excretion (UIE) on both days. RESULTS The median 24-h UIE on day four and day seven of the LID were not significantly different (36.1[IQR 25.4 - 51.2]mcg and 36.5[IQR 23.9 - 47.7]mcg, respectively, P=0.43). On day four of the LID, 72.1% of the DTC patients were adequately prepared (24-h UIE<50 mcg), and 82.0% of the DTC patients on day seven(P=0.18). Compared to the self-reported regular diet, DTC patients showed a significantly(P<0.01) lower percentage of nutrient intake (calories, protein, calcium, iodine, and water) during the LID. CONCLUSIONS The 24-h UIE on day four of the LID did not differ from day seven, and therefore shortening the LID from seven to four days seems justified to prepare DTC patients for 131I therapy in areas with sufficient iodine intake and may be beneficial to maintain a sufficient nutritional intake during DTC treatment.