Whole lung irradiation in stage IV Wilms tumor patients: Thyroid dosimetry and outcomes.

PURPOSE: To report the thyroid dosimetry and long-term follow-up of childhood cancer survivors treated with whole lung irradiation (WLI) for Wilms tumor. METHODS: Twenty-eight patients with pulmonary metastases from Wilms tumor who underwent WLI from 2000 TO 2012 at a single institution were reviewed. Radiation dose to the thyroid gland in each case was calculated. Postradiation thyroid function test (TFT) results and management of thyroid function abnormalities were extracted from the medical records. RESULTS: Median age at treatment was 5 years (range: 1-9 years), and median follow-up time was 74.1 months (7.2-198.4). The male/female ratio was 1:1.8. Complete dosimetry data were available for 22 of the 28 patients receiving WLI. Mean thyroid volume was 3.3 cc (range: 1-6.8). The average mean and median mean dose to the thyroid was 6.7 and 7.1 Gy, respectively (range: 1.3-11.7 Gy). Average max dose to the thyroid was 12.4 Gy (range: 7.8-20.3 Gy). Two patients were found to have a thyroid stimulating hormone (TSH) above the normal range, managed with levothyroxine. Another patient was found to have an isolated elevation of TSH which normalized without treatment. A fourth patient was found to have an enlarged thyroid on examination with no palpable nodules or abnormal TFTs. CONCLUSIONS: Average mean dose to the thyroid gland was 6.7 Gy for this population of stage IV Wilms tumor patients. There was a low rate of thyroid dysfunction, but limited follow-up. Attention to blocking the thyroid gland as much as possible when designing radiation fields can potentially mitigate the risks of long-term thyroid effects.