Malignant and benign thyroid nodules after total body irradiation preceding hematopoietic cell transplantation during childhood

Background: The risk of radiation-induced benign and malignant thyroid nodules is well known. Objective: The aim of this study was to determine the occurrence of thyroid nodules and carcinomas after fractionated total body irradiation (TBI) preceding hematopoietic stem cell transplantation (HSCT) for malignant hematological disease during childhood. Methods: We conducted a retrospective university hospital-based observational study. The participants were 76 patients receiving fractionated TBI between 1989 and 2009 as part of the conditioning regimen for HSCT to treat malignant hematological disease, with a median age of 8.2 (5.7-11.4) years, for whom the last ultrasound examination was performed at a median age of 14.2 (11.2-17) years. The main outcome measure was cumulative incidence of thyroid nodules detected by ultrasound scans followed by biopsy if necessary. Results: Thyroid nodules were examined in 21 (28%) patients, six (29%) of whom were diagnosed with thyroid carcinoma at the age of 2.2-18.6 years after TBI. The cumulative incidence of nodule occurrence increased with increasing time from diagnosis. The 10-year cumulative incidence of benign and malignant thyroid nodules was 16% (95% confidence interval (CI) 4-27%) and 8% (95% CI 0-16%) respectively. Seventeen (22%) patients had hypothyroidism (compensated n=12, in five patients it was transient). No significant independent risk factors were identified in the multivariable competing risk model as a function of nodule occurrence. Conclusion: Short-term and life-long monitoring, with screening for nodules of the thyroid gland using ultrasound scans, is recommended for survivors subjected to TBI for HSCT during childhood.