Professor Alice Sigurdson and Colleagues has reported the dosage difference which is required for treatment and the dosage which increases the risk of thyroid cancer.
The study was conducted in 72 patients who were treated for thyroid cancer during their childhood. The thyroid gland which is irradiated during childhood has greater risk of developing thyroid cancer and there seems to be a relationship between radiation and development of oncologic effects. The study documents the evidence of Chernobyl nuclear reactor explosion, in Belarus in which the girls under the age of 14 years who were irradiated by the radiation had a 30 percent more increased risk of thyroid cancer development. Papillary carcinoma was the most common type of cancer which occurs secondary to thyroid cancer.
Thyroid cancer occurrence is an increased secondary malignancy to Childhood Hodgkin's disease and neuroblastoma. Patients undergoing radiation in the neck regions for treatment of central nervous system cancer, acute lymphoblastic leukemia, Non-Hodgkins lymphoma, Ewing's sarcoma and Wilm's tumor develop thyroid cancer. Development of Malignant Hematological diseases is increased in children's who had whole body irradiation before bone marrow transplantation.
Ron et al, in 1995 had found that the risk of thyroid cancer development increased linearly with increasing doses to the thyroid during thyroid external X-ray or ã-irradiation. The study also reports that dose response relation appeared with the higher doses (>10Gy) associated with cancer therapy. Professor Sigurdson showed that the risk of thyroid cancer increased linearly with increasing therapeutic radiation doses in the low dose range up to 20 Gy, but it demonstrates a downturn in the dose response curve with a declining risk at doses greater than 30 Gy. The risk of thyroid cancer appeared to peak at 20-29 Gy with an odds ration of 9.8. The risk then fell to a low level at doses above 30 Gy. The study shows that widely held belief that lower doses of radiation reduces the late carcinogenic effects does not necessarily apply to the development of thyroid cancer. This point should make us give more thought to our therapeutic strategies that use ionizing radiation in future clinical studies. In view of the long latent interval and the fact that the risk of radiation associated thyroid cancer remains elevated for up to 30 years, the need for long term surveillance, should be monitored with thyroid ultrasonography, for all childhood cancer survivors who had therapeutic radiation of the neck.
Source: The Lancet.