Radiation Dose Predicts Growth Hormone Deficit

For children with brain tumors, dose, time after irradiation predicts growth hormone deficiency

WEDNESDAY, Nov. 2 (HealthDay News) -- For children with brain tumors, growth hormone deficiency (GHD) can be predicted by the time after conformal radiation therapy (CRT) and the mean radiation dose to the hypothalamus, according to a study published online Oct. 31 in the Journal of Clinical Oncology.

Thomas E. Merchant, D.O., Ph.D., from St. Jude Children's Research Hospital in Memphis, Tenn., and colleagues investigated GHD following CRT for 192 pediatric patients with localized primary brain tumors (ependymoma, low-grade glioma, craniopharyngioma, high-grade glioma, and other tumor types). Patients underwent testing of growth hormone secretion using secretogogues arginine and L-dopa before and six, 12, 36, and 60 months after CRT. Based on data from 118 patients, peak growth hormone was modeled as a function of mean dose of radiation to the hypothalamus and time after CRT.

The investigators found that 22.9 percent of tested children had pre-irradiation GHD at baseline. Based on modeling, at a dose of 60 Gy, an average patient was predicted to develop GHD after 12 months; for a dose of 25 to 30 Gy, development of GHD was predicted 36 months after CRT; for a dose of 15 to 20 Gy, GHD was predicted 60 months after CRT. In order to achieve a 50 percent risk of GHD at five years, the mean cumulative dose of radiation to the hypothalamus was 16.1 Gy.

"[Growth hormone] secretion after CRT can be predicted on the basis of dose and time after irradiation in pediatric patients with localized brain tumors," the authors write.

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