The utility of MR in planning the radiation therapy of oligodendroglioma.

Newer methods of radiation therapy for treating oligodendroglioma after surgical resection have produced promising results using high doses of radiation. However, these doses are close to those that cause necrosis of normal brain, making the accurate spatial localization of tissue at risk for containing tumor cells more important. Because MR imaging is superior to CT in detecting some types of intracranial disease, nine patients with oligodendroglioma were studied with both MR and CT. Results were compared with surgical findings. In six cases, MR identified some tumor volume found during surgery that was not detected by CT. In addition, the interface between abnormality (tumor plus edema) and normality was depicted much more clearly by MR than by CT in most cases. Such superior depiction of the margins of abnormality is important for radiation therapy planning because of the known tendency of oligodendroglioma to infiltrate adjacent edema, making all areas of abnormality potential tumor-bearing tissue. Finally, MR showed normal brain tissue in areas considered suspicious by CT, because they were not well seen on CT in several patients. In these cases of low-grade oligodendroglioma, MR was believed to be superior to CT in providing information needed for radiation therapy planning because of its ability to distinguish tumor and adjacent edema (considered tissue at risk for containing microscopic tumor) from contiguous normal brain.