Tumor volume response to radiation therapy in children with gliomas of the midbrain and brain stem

Serial tumor volume measurements were performed on CT or MR images of nine children treated with radiotherapy for gliomas of the midbrain or brain stem. Two types of initial tumor responses were observed. One group of four children showed an initial increase in the tumor volume within the first month following completion of radiotherapy, followed by gradual regression. These tumors were relatively large and located in the midbrain. The second group of five patients showed a continuous postreatment regression. This observation has therapeutic implications. The initial radiation field has to be large enough to encompass a possible tumor volume increase, and a posttreatment increase in tumor size is not equivalent with treatment failure