Incidence of primary hypothyroidism in patients exposed to therapeutic external beam radiation, where radiation portals include a part or whole of the thyroid gland

Breast cancer, breast cancer-directed radiation therapy and risk of hypothyroidism: A systematic review and meta-analysis

“…Measures of the relative risk (risk ratios, odds ratios, incidence rate ratios, hazard ratios) were considered equivalent given the rare outcome. Where adjusted effect estimates were not provided, raw data were used to calculate the crude estimates and 95% confidence intervals (CI) [8,[16][17][18][19][20][21]. Raw data calculations are available upon request.…”

“…In total, 34 full text papers were assessed for eligibility. After excluding 14 papers [7,[22][23][24][25][26][27][28][29][30][31][32][33][34], 20 studies were included in the systematic review [8][9][10][16][17][18][19][20][21][35][36][37][38][39][40][41][42][43][44][45]. Of these, 12 were included in one or several of the meta-analyses.…”

“…An overview of the characteristics of the included studies is provided in Table 1. Nineteen studies were cohort studies [8][9][10][16][17][18][19][20][35][36][37][38][39][40][41][42][43][44][45] and one was a randomized trial where patients were randomized to chest wall/breast radiation with or without supraclavicular radiation therapy [21]. The studies were conducted in 15 different countries and published between 1985 and 2021; most studies were published after 2010 (15 studies).…”

“…The definition and way of measuring hypothyroidism varied considerably (see Supplementary Table 4). Sixteen studies evaluated thyroid function using biochemical methods such as serum values of TSH, fT4 and free T3 (fT3) [10,[16][17][18][19][20][21][35][36][37][38][39][41][42][43]45]. Of these, eleven studies used serum concentrations of TSH, fT4 and/or fT3 to define a diagnosis of hypothyroidism, while five studies used elevated TSH levels only.…”

“…None of these were included in the meta-analyses. Nine studies [8,9,[16][17][18][19]40,43,44] focused on the risk of hypothyroidism in breast cancer survivors versus the general population; three reported on the risk of hypothyroidism after radiation therapy compared with no radiation therapy [8,16,44]. Six studies reported the risk of hypothyroidism according to radiation therapy modality (i.e., radiation to breast/chest wall only vs. radiation to supraclavicular lymph nodes) [8,10,16,20,21,44].…”