Total or near-total thyroidectomy facilitates one-time removal of multifocal lesions; facilitates postoperative monitoring of tumor recurrence and metastasis; facilitates postoperative radioactive iodine-131 therapy; facilitates reduction of the probability of tumor recurrence and reoperation; and facilitates accurate assessment of the patient’s postoperative staging and risk stratification. For those who are operated as benign thyroid disease but have postoperative pathological diagnosis of DTC, the TNM staging of the tumor and risk stratification of recurrence, the risk of reoperation, the convenience of follow-up, and the patient’s willingness and compliance should be taken into account. A comprehensive analysis should be performed to determine whether to operate again.
Risk of recurrence stratification for differentiated thyroid cancer.
Postoperative staging and risk of recurrence stratification of DTC helps predict patient prognosis; guide the development of individualized treatment plans after surgery, including radioactive iodine-131 therapy and TSH suppression therapy to reduce recurrence rates and mortality; and guide the development of individualized follow-up plans.
Low risk who meet all of the following criteria.
No local or distant metastases.
All tumors visible to the naked eye have been completely removed.
The tumor does not invade surrounding tissues.
The tumor is not an aggressive histologic subtype and there is no vascular invasion.
If this patient has a whole-body B1I image after removal of postoperative residual thyroid tissue (referred to as clear nail), no iodine uptake is found outside the thyroid bed.
Intermediate risk if any of the following conditions are met.
Initial surgical pathology can reveal microscopically a tumor with peri-thyroidal soft tissue invasion.
Abnormal radioactivity uptake is found in cervical lymph node metastasis or whole body “1I” imaging after nail clearance.
The tumor is of an aggressive histological type or has vascular invasion.
With BRAF-v600E mutation.
High risk if any of the following conditions are met.
The tumor is visible to the naked eye invading surrounding tissues or organs.
The tumor was not completely resected and there is intraoperative residual.
With distant metastasis.
Serum Tg level is still high after total thyroidectomy.
Significance of postoperative radioactive iodine-131 smelting therapy.
Radioactive iodine-131 treatment for DTC can be divided into nail clearing treatment using iodine-131 to remove residual thyroid tissue after surgery and nail clearing treatment using iodine-131 to remove metastatic foci of DTC that cannot be removed by surgery.
The significance of postoperative nail clearing for DTC.
(1) Facilitate postoperative follow-up monitoring. Iodine-131 can remove normal thyroid tissue that remains from surgery or cannot be removed (e.g. for the protection of parathyroid glands, laryngeal recurrent nerve, etc.), which is beneficial to the monitoring of serum thyroglobulin (Tg) in DTC patients and improves the sensitivity of iodine-131 whole-body imaging (WBS) for the diagnosis of iodine-intake DTC metastases.
(2) Nail clearance is the basis of focal clearance treatment and facilitates postoperative iodine-131 focal clearance treatment. The completion of nail clearing helps DTC metastases to uptake iodine more effectively.
(3) It is beneficial to the re-staging of DTC after surgery. Iodine-131 WBS and SPECT/CT fusion imaging after nail clearing can detect some of the cervical lymph node metastases or even distant metastases from iodine-131 uptake, and thus can change the staging and risk stratification of DTC.
(4) DTC is often characterized by bilateral, micro multifocal, long local latency and development period, and high recurrence rate. Nail clearing treatment is useful for the removal of microscopic cancer foci hidden in postoperative residual thyroid tissue, occult metastases that have invaded beyond the thyroid gland, or potential DTC foci that cannot be removed because the condition does not allow or surgery.
Treatment with radioactive iodine-131 after DTC surgery can achieve excellent results and improve the prognosis, including delaying the time to recurrence, reducing the recurrence rate and decreasing distant metastasis. Radioactive iodine-131 treatment has its limitations, and factors such as the age of onset of DTC patients, the uptake and retention time of radioactive iodine-131 by the lesion, radiation sensitivity, and patients’ adverse reactions to multiple treatments of radioactive iodine-131 can affect the treatment outcome. The reason for the limited therapeutic effect of radioiodine-131 in some high-risk DTC is that most of the DTC cells with distant DTC metastases or in the progressive stage have developed a dedifferentiated state, and the ability to take up and retain radioiodine-131 is reduced or even lost.
Whether to do radioactive iodine-131 treatment after surgery.
Iodine-131 clearing treatment is required for those who have obvious invasion of tissues around cancer tissue (visible intraoperatively), lymph node metastasis or distant metastasis (such as lung, bone, brain and other organs). Smaller tumors (≤1 cm) without significant invasion of surrounding tissues, lymph node metastasis or other invasive features may not be recommended for nail scavenging treatment.
Contraindications to radioactive iodine-131 therapy.
If there is an indication for nail clearing treatment, but excessive residual thyroid tissue is found during the pre-treatment evaluation, reoperation should be recommended first to remove as much residual thyroid tissue as possible; otherwise, nail clearing is less effective and multiple nail clearing treatments may be required to completely remove residual thyroid tissue. Although nail clearing treatment can remove residual thyroid, it is not recommended as an alternative to surgery.
If surgically resectable DTC metastases are identified during the evaluation prior to nail clearing, reoperation should be performed first. In cases where the patient has a contraindication to reoperation or refuses to undergo reoperation, or where the surgeon has assessed that reoperation is not appropriate, direct nail clearance may be considered. In patients with a large amount of residual thyroid tissue, nail clearing should be performed to prevent anterior cervical edema and radiation thyroiditis, and glucocorticoids may be given, or lower doses of nail clearing may be used. In patients with poor general status, concomitant other serious diseases or other high-risk malignancies, correct the general status and treat the concomitant diseases first, and then consider nail clearing treatment afterwards.
When to perform radioactive iodine-131 treatment after surgery.
Serum TSH level needs to be elevated before nail clearing treatment. When serum TSH>30 mU/L can significantly increase the uptake of iodine-131 by DTC tumor tissues.
Elevation of endogenous TSH can be achieved by either not taking thyroxine medication postoperatively and administering iodine-131 nail therapy approximately 4 weeks postoperatively, or by taking thyroxine medication postoperatively and stopping it at an elective date for iodine-131 nail clearing therapy. There was no significant difference between postoperative thyroid hormone supplementation followed by discontinuation and receiving iodine-131 therapy without thyroid hormone supplementation (3 to 4 weeks postoperatively) in terms of wound recovery, iodine-131 efficacy and occurrence of adverse effects in patients.
Administration of exogenous TSH method: Recombinant human thyroid stimulating hormone (rhTSH) is given to raise the patient’s serum TSH level. This method can avoid the discomfort associated with hypothyroidism (referred to as hypothyroidism) after discontinuation of thyroxine.
The efficacy of iodine-131 is dependent on the dose of iodine-131 entering the residual thyroid tissue and within the DTC lesion. Since stable iodine ions in the body compete with iodine-131 to enter the thyroid tissue and DTC lesions, patients need to be on a low iodine diet (<50 μg/d) for at least 1 to 2 weeks prior to treatment, with special attention to avoid enhanced CT examinations. If an enhanced CT examination has been performed, it is recommended that iodine-131 treatment be administered 1 to 2 months later.
Common adverse reactions in the short term (1-15 d) after nail clearing treatment include: weakness, neck swelling and pharyngeal discomfort, dry mouth or even swollen salivary glands, altered taste, nasolacrimal duct obstruction, epigastric discomfort or even nausea, and urinary tract injury. To reduce the local inflammatory response, oral prednisone, 15-30 mg/day, may be given for about 1 week in order to reduce the local inflammatory response.
A post-treatment whole-body radioiodine scan is usually performed within 2-10 days after iodine-131 nail scavenging treatment. Since the dose of iodine-131 used for nail scavenging is much higher than the dose of diagnostic whole-body radioiodine scan, DTC metastases can be detected by post-treatment whole-body radioiodine scan in 10% to 26% of patients who do not have DTC metastases on diagnostic whole-body radioiodine scan.
Usually, oral thyroxine is started (or continued) 24-72 h after nail clearing treatment, and the conventional dose is L-T4. For those who have more residual thyroid tissue before nail clearing, the radioactive iodine-131 of nail clearing can destroy the thyroid tissue and release thyroid hormone into the blood, so the starting time of L-T4 treatment can be postponed appropriately, and the dose of L-T4 supplementation should be increased gradually for those who are old or have underlying diseases.
The thyroid hormone, TSH, Tg, and TgAb levels should be monitored to understand the changes in Tg, adjust the thyroxine dose, and control TSH to the corresponding suppression level. If necessary, add neck ultrasound to monitor the changes of suspected metastatic lymph nodes after iodine-131 treatment. At about 6 months of treatment, an assessment of the success of nail clearance can be performed. T4 should be discontinued for 3 to 4 weeks or triiodothyronine (L) for 2 weeks prior to follow-up.