In addition to dosimetric factors, deficiency symptoms of certain macro- and micronutrients may occur in the context of tumor- or treatment-related malnutrition, favoring the development of hypothyroidism [9]: Among these are iodine (important component of fT3 and fT4), iron (required for thyroid hormone formation) [9–13], selenium (regulation of the conversion of fT4 to fT3) [14], and amino acids (needed for the formation of free thyroid hormones) [15]. This evidence concerns the gene TG and hypothyroidism.