2.1. Study population and data collection

In this prospective hospital-based study, subjects were enrolled from among patients with papillary or follicular thyroid cancer who were administered more than 1.1 GBq (30 mCi) of RAI at the Chang Gung Memorial Hospital, Keelung, Taiwan from April 2012 to March 2014. All study participants had to be isolated in the¹³¹I ward at the Chang Gung Memorial Hospital. The Chang Gung Memorial Hospital Institutional Review Board (IRB) approved the study (No. 101–0188B). Confidentiality of the research subjects was maintained in accordance with the requirements of the IRB of the Chang Gung Memorial Hospital, and all research was conducted in accordance with the principles of the Declaration of Helsinki. Written informed consent was obtained from all study participants before their enrollment. All patients underwent total or complete thyroidectomy. The term “total thyroidectomy” refers to total or near-total thyroidectomy with or without central compartment and selective bilateral neck lymph node dissection. A low iodine diet for approximately 2 weeks before treatment was suggested for patients undergoing RAI therapy. Thyrotropin stimulation or thyroxine withdrawal was performed before RAI therapy. If thyroxine withdrawal was planned before RAI therapy, thyroid hormone (LT4) was withdrawn for 4 to 6 weeks. If thyrotropin stimulation was performed, recombinant human thyroid-stimulating hormone (rhTSH) (thyrogen 0.9 mg) was administered in a course of 2 consecutive daily injections, and RAI therapy was administered 24 hours after the second dose of rhTSH.

All patients in the study had a stimulated TSH >48 mIU/L at the time of RAI therapy. Patient characteristics were recorded, including age, sex, body weight, height, tumor size, serum stimulated thyroglobulin (Tg) level at diagnosis, and serum stimulated Tg level before RAI treatment in this study, and renal function. Tg was detected with an immunoradiometric assay (IRMA) kit (CIS Bio International, Gif-sur-Yvette, France). The detection limit of the Tg kit is 0.5 ng/mL, and its functional sensitivity has been assessed in our laboratory to be 1.2 ng/mL. All the patients were asked to drink at least 2 to 3 L of water for faster RAI elimination after treatment. Patients with heavy weight were not asked to drink more water in this study. All patients were discharged after a stay of 2 days in the ¹³¹I isolation ward, and the dose rate was less than 50 μSv/h detected from a distance of 1 m. The patients were instructed to remain at home and avoid public places for 1 week after discharge from the hospital. Patients were provided Radiation Safety Instructions upon discharge, and received instructions to stay more than 1 m away from their adult family members and caregivers, and to stay more than 3 m away from infants, young children, and pregnant women. The patients were directed not to share food, toothbrushes, towels, spoons, forks, chopsticks, glasses, or dishes with others. They were asked to flush the toilet 3 times after each use, and men were instructed to sit down to urinate and to keep the bathroom clean. On the 8th day after RAI treatment, the patients returned to the hospital and underwent whole body scanning. The results of the whole body scan were recorded as local (neck area), distant (other than neck area), and negative uptake of ¹³¹I.

The enrolled patients were asked to place a thermoluminescent dosimeter (TLD) in the living room, bedroom, and bathroom of their houses for 4 weeks to measure radiation exposure upon the patients’ discharge. We used TLDs 7776, which were the commercial product made by Thermo Harshaw. One dosimeter card consisted of 4 TLD chips. The dosimeters were read by the reader 8800 plus in the Institute of Nuclear Research,Taiwan. A total of 52 patients completed the study with the reading of the TLD after their completion of RAI therapy. Forty-three patients received 100 mCi (3.7 GBq), 6 patients received 70 mCi (2.6 GBq), and the other 3 patients received 150 mCi (5.6 GBq) RAI. At first, we would like to include all the 52 patients in this study. Finally, we included 43 patients undergoing 3.7 GBq (100 mCi) RAI and excluded those treated by 2.6 GBq (70 mCi) (6 patients) and 5.55 GBq (150 mCi) (3 patients) to keep data consistency and to avoid unnecessary confounding factor. Among the 43 included patients who underwent 3.7 GBq (100 mCi) RAI, there were 25 women and 18 men with a mean age of 51 ± 13 years.