The Dose of Radioactive Iodine Needed to Ablate the Thyroid Remnant Left Behind After Thyroidectomy
The Dose of Radioactive Iodine Needed to Ablate the Thyroid Remnant Left Behind After Thyroidectomy
The thyroid cells take up iodine, and radioactive iodine is commonly used to irradiate
 residual thyroid tissue and thyroid cancer following surgical removal of the thyroid gland
 (thyroidectomy). A whole body radioactive iodine scanning is usually carried out after
 thyroidectomy to assess the amount of thyroid tissue left behind at surgery (that might still
 contain cancer), and to evaluate the presence of iodine avid lesions elsewhere in the body
 (that might be cancer metastases). A large dose of radioactive iodine is often given, still
 the optimal iodine dose to ablate the thyroid remnant after surgery is not known. In this
 study, two radioactive iodine doses are compared in the ablation of the thyroid remnant, a
 smaller (1110 MBq) dose and a larger (3700 MBq) dose. The study participants are randomly
 allocated using a 1:1 ratio to receive either the smaller or the larger radioactive iodine
 dose. These treatments are compared for safety, adverse effects, and the need for subsequent
 repeat treatments. The individual absorbed radiation doses are measured. The study hypothesis
 is that fewer repeat radioiodine treatments might be needed after the larger dose, but the
 larger dose might be associated with a higher frequency of adverse events.
The study participants are randomly allocated to receive either a 1110 MBq or a 3700 MBq dose
 of radioiodine (131I) approximately 5 weeks after thyroidectomy. Thyroxin substitution is
 initiated only after administration of radioactive iodine. Treatment efficacy is monitored
 using serum thyroglobulin measurements and whole body radioiodine scanning. The absorbed
 radiation dose at the thyroid remnant and the biological half-life of radioactive iodine are
 measured with SPECT, 131I iodine detector and a Geiger counter.

 Treatment related adverse events are collected using structured forms 4 to 5 days, 2 weeks
 and 3 months after administration of radioiodine. The need for a repeat treatment is assessed
 4 to 6 months after the first administration of radioiodine. The criteria for a repeat
 radioiodine treatment are serum thyroglobulin > 1 ug/L and/or presence of abnormal
 radioiodine uptake in a whole body radioiodine scanning, which is carried out following a
 4-week interruption of thyroxin supplementation or following administration of rhTSH.

 Number of patients: 160

 Aims of the study:

 -  To find out weather the risk for second radioiodine treatment differs with two dose
 levels of radioiodine: 1110 MBq or 3700 MBq.

 -  To study possible differences in the adverse effects in the treatment groups. Also days
 at hospital are counted.

 -  To analyse the effect of absorbed radiation dose to the treatment results
Inclusion criteria:

 -  Total or near total thyroidectomy performed for papillary or follicular thyroid cancer

 -  R0-1 resection, no macroscopic cancer left behind at surgery

 -  Physically and emotionally able to undergo radioiodine treatment

 -  A written informed consent

 Exclusion criteria:

 -  Pregnancy

 -  Physical or psychiatric illness that may deteriorate during the isolation period
 required by radioiodine therapy