To compare survival and toxicity in adult patients treated with low-dose (50.4 Gy/28 fractions) versus high-dose (64.8 Gy/36 fractions) localized radiation therapy (RT) for supratentorial low-grade astrocytoma, oligodendroglioma, and mixed oligoastrocytoma.

From 1986 to 1994, 203 eligible/analyzable patients were randomized: 101 to low-dose RT, 102 to high-dose RT. Almost half were younger than 40 years, and 95% had grade 2 tumors. Histologic subtype was astrocytoma (or mixed oligo-astrocytoma with astrocytoma dominant) in 32% of patients and oligodendroglioma (or oligoastrocytoma with oligodendroglioma dominant) in 68%. Tumor diameter was less than 5 cm in 35% of patients, and 41% of tumors showed some degree of contrast enhancement. Extent of resection was gross total in 14% of patients, subtotal in 35%, and biopsy only in 51%.

At the time of the present analysis, 83 patients (41%) are dead, and median follow-up is 6.43 years in the 120 who are still alive. Survival at 2 and 5 years is nonsignificantly better with low-dose RT; survival at 2 and 5 years was 94% and 72%, respectively, with low-dose RT and 85% and 64%, respectively, with high-dose RT (log rank P =.48). Multivariate analysis identified histologic subtype, tumor size, and age as the most significant prognostic factors. Survival is significantly better in patients who are younger than 40 years and in patients who have oligodendroglioma or oligo-dominant histology. Grade 3 to 5 radiation neurotoxicity (necrosis) was observed in seven patients, with one fatality in each treatment arm. The 2-year actuarial incidence of grade 3 to 5 radiation necrosis was 2.5% with low-dose RT and 5% with high-dose RT.

This phase III prospective randomized trial of low- versus high-dose radiation therapy for adults with supratentorial low-grade astrocytoma, oligodendroglioma, and oligoastrocytoma found somewhat lower survival and slightly higher incidence of radiation necrosis in the high-dose RT arm. The most important prognostic factors for survival are histologic subtype, tumor size, and age. The study design of the ongoing intergroup trial in this population will be discussed.