Patterns of failure following CT-based 3-D irradiation for malignant glioma

Background: This retrospective study was undertaken to analyze the patterns of failure in patients with malignant glioma after Localized irradiation. Patients and Materials: Recurrence patterns of 46 patients with malignant g lioma (glioblastoma: 24, anaplastic astrocytoma: 15, anaplastic oligodendro glioma: 5, unclassified malignant glioma: 2) were studied using CT/MR scans and radiotherapy plan-plots. ALL patients were operated before and a total dose of 5,940 cGy was given after CT assisted and individually configurate d 3-D planning using 7-15 slices at an in between distance of 5 mm. The tar get volume included a 2-3 cm margin beyond the tumor indicated by preoperat ive CT scan. The following parameters were analyzed: tumor size and type, s ize of perifocal edema and whether the edema was fully included into treatm ent volume and finally the Location of the recurrent tumor. The maximal dis tance between primary tumor and recurrent tumor was measured and also the d istance from the border of the primary tumor to the distant border of edema for a visual analysis. Results: Local limited volume irradiation was sufficient since 73.9% of rec urrences occurred within 2 cm distance from primary tumor and 93.5% of recu rrences occurred completely within 3 cm distance from primary tumor. Regard ing the distance between primary tumor and recurrent tumor and the time int erval until appearance of recurrent tumor it was not of importance if perif ocal edema was included completely into treatment volume or not. Conclusion: Limited volume irradiation of malignant glioma with a target vo lume 3 cm beyond that indicated by preoperative CT scan seems to be suffici ent, since 93.5% of recurrences were completely within 3 cm distance from t he margin of the tumor. Improvement of the results with larger treatment vo lumes are unlikely. Complete irradiation of perifocal edema was not found t o be necessary.