PATTERNS OF TUMOR PROGRESSION AFTER RADIOTHERAPY FOR LOW-GRADE GLIOMAS - ANALYSIS FROM THE COMPUTED-TOMOGRAPHY MAGNETIC-RESONANCE-IMAGING ERA

Postoperative radiotherapy for low-grade gliomas has been shown in ret rospective series to improve survival, compared with surgery alone. To determine the proper radiotherapy treatment volume and dose, an under standing of the patterns of failure with current radiotherapy techniqu es is necessary. We studied 30 consecutive patients who had a patholog ic diagnosis of low-grade nonpilocytic glioma treated in our departmen t between 1975 and 1994. Before radiotherapy, 5 patients underwent bio psy, 22 had subtotal resection, and 3 had gross total excision. All ha d pre-and posttreatment computed tomographic (CT) or magnetic resonanc e imaging (MRI) scanning. Megavoltage radiotherapy was delivered to sh rinking partial (22 patients) or whole-brain (8 patients) fields. Medi an dose was 59.4 Gy (range, 46.4-64 Gy) in 1.8- to 2-Gy fractions. Med ian follow-up was 44 months (3-215 months) for the cohort and 105 mont hs for survivors. For the entire series, 5-year overall survival and r elapse-free survival rates were 50% and 41%, respectively. Sixteen pat ients (53%) progressed at a median of 30 months. At the time of failur e, 71% (5 of 7) of pathologically evaluated tumors were of high grade. Recurrence originated within the field in all patients. Higher 5-year overall survival and relapse-free survival rates were associated (p < 0.001) with preradiotherapy functional status 1 versus functional sta tus 2 through 4 (60% vs. 0% and 55% vs. 0%, respectively). Seizure as initial presentation was favorable over other symptoms (5-year overall survival, 64% versus 14%; p = 0.057). We conclude that 1) low-grade n onpilocytic gliomas can transform to high-grade lesions after treatmen t with conventional radiotherapy, 2) recurrence uniformly occurs withi n the treatment volume, and 3) pretreatment functional status correlat es prognostically with survival. The local pattern of failure suggests that radiotherapy dose escalation within conformal fields could impro ve results.