The magnitude and severity of the damage caused by the March 11 earthquake in Japan is rare, and the nuclear radiation caused by the explosion of the nuclear power plant, which is a secondary disaster, has raised strong concerns. Experience and lessons learned show that among malignant tumors caused by nuclear radiation, thyroid cancer, especially in children and adolescents, is the most prominent, and the main pathological type is papillary thyroid cancer. Therefore, the relationship between radioactive substances and thyroid cancer has become the focus of media attention and reports. Wei Songfeng, Department of Thyroid Neck Oncology, Tianjin Cancer Hospital
In the etiological study of thyroid cancer, radioactive radiation carcinogenesis has become the most definite cause of thyroid cancer. It is generally believed to affect only adolescents before the age of 15, while they are not threatened by it after the age of 15. Radioactive nuclear substances affect the environment and human beings mainly through the atmosphere, water and biological chain. The effects of radioactive clouds of smoke (mainly iodine and cesium) on human beings come from the low-dose external exposure caused by them on the one hand, and from the internal exposure caused by the ingestion of food and water contaminated with radioactive substances on the other hand, with the latter having a longer duration of action and a greater impact on human beings. If you drink contaminated water or eat contaminated food, some of the radioactive elements will be deposited in the body, causing the cells of the body to change at the genetic level, and the changed cells will produce some subclonal cells during the regeneration process, and then cancer will occur, and the chance of such cancer induction is proportional to the dose received.
Several studies have shown that the thyroid is one of the organs most susceptible to radionuclide induced malignancies. The most detailed study of radionuclides and thyroid cancer comes from the area affected by the nuclear accident at the Chernobyl power plant in the former Soviet Union, which released 40 MCi of radioactive material into the environment for 10 days in 1986, when the worst radioactive fallout was in northern Ukraine and southern Belarus. Radioactive iodine played a 90% role in the impact of the Chernobyl accident, which resulted in more than 5,000 cases of thyroid cancer in children, aged 0-18 years at the time of the nuclear accident. Their intake of radioactive iodine was mainly from contaminated vegetables and dairy products. The first case of associated thyroid cancer was reported in 1990, the fourth year after the accident, and cases have since emerged, with the incidence of thyroid cancer in children increasing rapidly, from 1 in 1 million to over 30 in 1 million per year in Belarus by 1996. The incidence rate in the Gomel region of Belarus increased to 1 per 1 million due to high doses of contamination. Chernobyl mainly affects adolescents, mainly because of their rapid growth and the higher number of cells in their tissues and organs that are in the process of division, and thus the much higher possibility of genetic coding errors and damage due to radiation. Fetuses, in particular, have the fastest cell division, and the effects of radiation are most pronounced. Secondly, children, who are more exposed to radiation, are 3-5 times more likely to get thyroid cancer after several years. Molecular etiological studies have shown that the molecular etiology of radiation-induced papillary thyroid cancer is mainly characterized by chromosomal gene rearrangements, i.e. RET/PTC gene rearrangements, which are different from point mutations (BRAF, RAS, etc.) often detected in papillary thyroid cancer induced by other etiologies or in other age groups. This difference in etiology and molecular etiology may determine the difference in clinico-biological behavior.
The lessons learned from Chernobyl cannot be simply applied to this event. Currently, the nuclear power plant accident in Japan is classified as level 5, while Chernobyl is level 7 (the most severe level), and if the nuclear leak is not aggravated, the total amount of leaked nuclear material between the two will be several orders of magnitude different. The current level of protection and treatment is not the same as that in the 1980s. We should pay attention to radiation protection, especially for people under 20 years of age, but there is no need to be overly nervous. The following are some of our recommendations.
The first is the cancer prevention perspective of the general population. Some media suggest that in order to improve daily radiation protection, you can consume more foods with high iodine content such as seaweed, nori and iodized salt. Theoretically, taking more stable iodine can competitively reduce the intake of the radioactive nuclear substance iodine 131, thus reducing the direct damage to the thyroid gland from “internal irradiation” after the nuclear substance is taken up and gathered by the thyroid gland. However, the dose of iodine required to achieve this goal is so large that iodine intake, such as regular iodized salt, has limited “competitive power”. Increased iodine intake has little preventive value against “external exposure” to other nuclear substances, and is even less valuable in adults because radiation-induced thyroid cancer rarely occurs. In addition, many studies have shown that long-term consumption of foods high in iodine, especially in coastal areas, may increase the incidence of papillary thyroid cancer and other thyroid-related diseases. It is important to take everything in moderation. The general public may go to the hospital to have their thyroid checked out out of fear, but it should be noted that even if a swelling is found in the thyroid gland, it should not be blindly assumed that it is a malignant tumor and must be treated by surgery, because the incidence of thyroid nodules increases with age at a rate of 0.08% per year. Clinically, the incidence of thyroid nodules in the normal adult population is 4-7%, with some reports exceeding 10%. The most common and effective means of examining the thyroid gland in China is color ultrasound Doppler, and experienced head and neck ultrasonographers have a correct diagnosis of benign and malignant thyroid nodules of over 90%.
From a professional point of view, once thyroid cancer in children and adolescents is diagnosed, it is important to ask carefully whether there is a clear history of radiation exposure, including X-rays, because the clinical biology and molecular etiology of adolescent thyroid cancer caused by radiation are often different from those of thyroid cancer of other etiologies, and thus the principles of clinical treatment should also be different. According to the Chernobyl experience, thyroid cancer caused by nuclear radiation is usually bilateral thyroid involvement, the lesions are often multifocal, and although the lethality remains unchanged, the growth rate is rapid, and the thyroid is more likely to invade the thyroid peritoneum and metastasize to regional lymph nodes. Therefore, clinical management emphasizes total thyroidectomy with appropriate cervical lymph node dissection. As a professional colleague, we should conduct careful and adequate preoperative examination and evaluation of these patients, while continuously summarizing relevant experience, and finally provide scientific, standardized and reasonable treatment to these “young patients”.