Dosimetry and growth hormone deficiency following cranial irradiation of childhood brain tumors

Background, Dosimetry of the hypothalamus-pituitary (HP) region could allow prediction of the risk of growth hormone deficiency (CHD) following crania l irradiation. Procedure. Nineteen children (15 boys) with a median age of 6.3 years (range 1.7-16.5) at the time of irradiation of a brain tumor not involving the HP axis were followed for 1.2-6.3 years (median 3.4) from rad iotherapy (RT). The dose to a standardized anatomical model including the H P region was calculated from dose-volume histograms of 10% to 100% in steps of 10% of the HP model based on data from a computer-based treatment plann ing system, If GHD was suspected from insulin-like growth factor-I, serum i nsulin-like growth factor binding protein-3, and/or height velocity measure ments, an arginine stimulation test was performed. GHD was defined by a pea k GH <15mU/liter. Results. Ten patients developed GHD 10-26 months from irr adiation. Cox regression analysis identified the 90% dose-volume of the HP box as the strongest predictor of development of GHD (P = 0.03). The median dose to the 90% dose-volume of the HP region was 37.5 Gy (range 2.3-55.3). The cumulated risk of GHD 2.5 years after radiotherapy for children receiv ing more than and less than 37.5 Gy to the HP region was 87% and 33%, respe ctively (P = 0.036). Conclusions. Dosimetry of a defined HP volume provides the opportunity to 1) calculate the exact dose delivered to this region; 2 ) predict the risk of GHD and, 3) in the future revise the treatment planni ng and thus reduce the risk of endocrine adverse effects. Med. Pediatr. Onc ol. 33:564-571, 1999. (C) 1999 Wiley-Liss, Inc.