Comparison of hypothyroidism, growth hormone deficiency, and adrenal insufficiency following proton and photon radiotherapy in children with medulloblastoma

Background: Endocrine deficiencies are common following Craniospinal irradiation (CSI) in children with brain tumors, but empirical data comparing outcomes following proton (PRT) and photon radiation therapy (XRT) are limited. Methods: This retrospective chart review compared the incidence of hypothyroidism, Growth hormone deficiency (GHD), and Adrenal insufficiency (AI) in patients with medulloblastoma treated with XRT and PRT between 1997 and 2016. All patients received CSI and had routine endocrine screening labs to evaluate for thyroid dysfunction, GHD, and AI. We used proportional hazards regression to calculate hazard ratios (HR) and 95% confidence intervals (CI) comparing the development of hypothyroidism, AI, and GHD between radiation modalities, adjusting for age at diagnosis, sex, race/ethnicity, and CSI dose. Results: We identified 118 patients with medulloblastoma who were followed for a median of 5.6 years from the end of radiotherapy. Thirty-five (31%) patients developed hypothyroidism, 71 (66%) GHD, and 20 (18%) AI. Compared to PRT, XRT was associated with a higher incidence of primary hypothyroidism (28% vs. 6%; HR = 4.61, 95% CI 1.2–17.7, p = 0.03). Central hypothyroidism, GHD, and AI incidence rates were similar between the groups. Conclusions: Primary hypothyroidism occurs less often after PRT CSI, compared to XRT CSI. This suggests that the thyroid and pituitary glands receive less radiation after spine and posterior fossa boost RT, respectively, using PRT.