Malignant glioma--timing of response to radiation therapy.

PURPOSE: The response of malignant gliomas to radiation was examined retrospectively in 71 patients with newly diagnosed supratentorial malignant gliomas. Questions asked included frequency, timing and clinical significance of response. METHODS AND MATERIALS: After surgery, all were treated with whole brain plus boost radiotherapy followed 8 weeks later by chemotherapy. The rate, degree, and timing of response to radiation were determined by comparing postoperative, end of radiation, and prechemotherapy CT scans on each patient.
RESULTS: Postoperative residual tumor was evident on 63/71 postoperative scans. Twenty-two of 63 tumors (35%) had a partial or complete response to radiation. Twenty (32%) had responded by the end of radiation; 17 maximally. Six to 8 weeks later, three responding tumors had responded further and two previously stable ones had begun to respond. Only three tumors (5%) responded completely. A greater proportion of anaplastic gliomas than glioblastomas responded to radiation (52% vs. 26%). Protracted or delayed responses were only observed in patients with anaplastic glioma. Patients who responded to radiation did not live significantly longer than non-responders. However, tumor progression prior to chemotherapy was associated with significantly shorter survival.
CONCLUSION: This CT scan-based analysis demonstrates that malignant gliomas are only moderately radioresponsive tumors and also demonstrates that response to radiation, if it is going to occur, is usually evident by the end of treatment.