Influence of vitamin C on salivary absorbed dose of 131I in thyroid cancer patients: a prospective, randomized, single-blind, controlled trial.

UNLABELLED In this study, vitamin C was administered at various times as a sour stimulant to thyroid cancer patients, and the effect on salivary absorbed dose of therapeutic radioiodine ((131)I) was investigated. METHODS Patients with differentiated thyroid cancer who had been prepared for thyroid remnant ablation after total thyroidectomy were prospectively recruited and, using a random-number table, were divided into 4 groups. In the hypothyroid condition, the patients in groups A, B, C, and D began sucking vitamin C (100 mg every 4 h in the daytime over 6 d) at 1, 5, 13, and 25 h, respectively, after receiving 3.7 GBq of (131)I. Scintigraphic images of the head and neck were serially acquired after (131)I administration to assess biokinetics in the salivary glands. Calculation of salivary absorbed dose was based on the MIRD schema of the Society of Nuclear Medicine. RESULTS Seventy-two patients (18, 18, 19, and 17 patients from groups A, B, C, and D, respectively) were eligible for the analysis of salivary dosimetry. Differences in absorbed doses to the parotid salivary gland (0.18 +/- 0.11, 0.16 +/- 0.07, 0.16 +/- 0.09, and 0.16 +/- 0.12 mGy/MBq in groups A, B, C, and D, respectively; P = 0.37) and submandibular salivary gland (0.19 +/- 0.05, 0.17 +/- 0.05, 0.18 +/- 0.07, and 0.17 +/- 0.06 mGy/MBq, respectively; P = 0.28) were not statistically significant among groups. Salivary cumulated activities arising from the first 24 h after (131)I administration accounted for 86.08% +/- 7.89% (range, 75%-98%) of total cumulated activities. Differences in salivary absorbed dose during the first 24 h were not statistically significant among the 4 groups either (P = 0.32 and 0.24, respectively, for the parotid and submandibular salivary glands). CONCLUSION Salivary stimulation with vitamin C at any time after (131)I administration has only a limited effect on salivary absorbed dose in thyroid cancer patients.