HYPERFRACTIONATED AND HYPOFRACTIONATED RADIATION-THERAPY FOR HUMAN-MALIGNANT GLIOMA XENOGRAFT IN NUDE-MICE

Xenografts of a human malignant glioma subcutaneously transplanted int o nude mice were irradiated with graded single doses (2, 5, 10 or 20 G y) or five types of fractionation schedules in two weeks: conventional [20 Gy in 10 fractions (fr)], hyperfractionated [24 Gy in 20 fr (two fractions per day)], and hypofractionated-1, 2, 3 [20 Gy, 18 Gy, 16 Gy in 4 fr]. All of the fractionated irradiation groups showed tumor reg ression. The hypofractionation-l group (20 Gy in 4 fr) demonstrated th e most prominent tumor regression, while the hyperfractionation group (24 Gy in 20 fr) showed the least effect. The hypofractionation-2 grou p (18 Gy in 4 fr) showed similar regression to the conventional fracti onation group (20 Gy in 10 fr). Histologically, tumors in the control groups consisted of a homogenous population of small anaplastic cells, and only a small number of tumor cells were glial fibrillary acidic p rotein (GFAP)-positive. Following irradiation, the population of small anaplastic cells decreased and the percentage of GFAP-positive cells increased. Cellular pleomorphism became much more prominent after irra diation in all of the fractionated irradiation groups as compared with the graded single dose irradiation groups. In this study, hyperfracti onation was not effective against human glioma xenografts compared wit h conventional fractionation and hypofractionation. This indicates tha t care is needed in applying hyperfractionation regimens to human mali gnant gliomas.