Malignant astrocytomas: focal tumor recurrence after focal external beam radiation therapy

Hochberg and Pruitt have reported glioblastomas recurring within 2 cm of the primary site in 90% of patients after whole-brain radiation therapy. They suggested that computerized tomography (CT) scan accuracy would permit smaller radiation fields. A treatment protocol with smaller-field focal brain irradiation following surgical resection is reported. The first 4500 cGy of radiation is focused to within a 3-cm margin around the tumor, with a 1500-cGy boost within a 1.5-cm margin. Forty-two patients with grade III or IV astrocytoma, treated with focal brain radiation therapy were reviewed retrospectively to assess patterns of tumor recurrence. Thirty patients received intra-arterial bromodeoxyuridine (BUdR) radiosensitization with focal brain radiation therapy, and 12 patients underwent conventional focal brain radiation therapy. Tumor margin was defined on preoperative and recurrence CT scans as the contrast-enhanced area; these were traced on acetate templates and compared with each other and with the actual scans. In all 42 patients, the lesion recurred within a 2-cm margin of the original tumor. Four patients had two recurrent areas: the second area was within the 2-cm margin in two, and outside this margin in two. These results are similar to those of Hochberg and Pruitt. It is suggested that focal irradiation is now the optimal treatment for malignant astrocytoma. Since recurrences continue to be within the irradiated volumes, it appears that higher focal doses of radiation are appropriate for clinical treatment trials of malignant astrocytomas.