Radiation Therapy or Combination Chemotherapy in Treating Patients With Clinically or Radiologically Progressive Low-Grade Gliomas

DISEASE CHARACTERISTICS: * Histologically confirmed low-grade glioma, of 1 of the following histologic subtypes: * Pilocytic astrocytoma I° and variants * Subependymal giant cell astrocytoma I° * Dysembryoplastic neuroepithelial tumor I° * Desmoplastic infantile ganglioglioma I° * Ganglioglioma I° and II° * Pleomorphic xanthoastrocytoma II° * Oligodendroglioma II° * Oligoastrocytoma II° * Astrocytoma II° * Fibrillary astrocytoma II° * Protoplasmatic astrocytoma II° * Gemistocytic astrocytoma II° * Children with chiasmatic-hypothalamic tumors may be eligible without histological diagnosis, if neuroradiologic findings meet unequivocal criteria for the presence of a low-grade glioma * Primary tumor localization: intracranial and/or spinal cord * No diffuse intrinsic tumors of the pons, even if histologically an astrocytoma I° or II° is diagnosed * Exception: pontine glioma II° in neurofibromatosis type 1 (NF1) disease allowed * Children presenting with disseminated low-grade glioma will be eligible for the study * All eligible patients without NF1 disease receiving chemotherapy as their first nonsurgical therapy are eligible for randomization * Children are eligible for the trial regardless of the presence of associated genetic disease: NF1 disease will be the prominent one, all children with NF1 disease are entered into the study arm III in case of an indication for nonsurgical therapy * Patients presenting with rare intracranial neoplas…