RADIOTHERAPY FOR SUPRATENTORIAL LOW-GRADE GLIOMAS - RESULTS AND PROGNOSTIC FACTORS WITH SPECIAL FOCUS ON TUMOR VOLUME PARAMETERS

From 1973 to 1990, 67 patients with a diagnosis of low-grade glioma were treated in our hospital. Overall survival was analysed as well as the influence of patient, tumour- and treatment-related factors with special focus on tumour volume parameters. Our study group included 49 patients treated by surgery and post-operative radiotherapy (RT) (40 patients) or post-biopsy irradiation alone (9 patients). Total or almost total resection was performed in 16 patients; partial excision was done in 24. With the available pre-surgery and pre-RT CT-scan and/or MRI images we were able to calculate tumour volumes by measuring the largest tumour dimensions in the three axes D1, D2, D3 and by assuming an ellipsoidal growth (i.e., tumour volume = D1D2D3pi/6). RT was delivered to involved regions: either the residual tumour volume or the tumour bed. The median RT dose was 56 Gy (45-60, range). The 60- and 90-month overall survival (Kaplan-Meier) was 79% and 67%, respectively. Female sex, > 70% Karnofsky (Kf) score, oligodendroglioma and < 71 cm3 (almost-equal-to 5 cm diameter sphere) tumour residuals before RT were associated with better overall survival rates (p < 0.05, log-rank). However, a Cox proportional hazards model showed that only the histological subtype and Kf significantly determined the patients' outcome: 60-month overall survival of 100%, 62%, 83% and 64% for oligodendrogliomas, mixed oligo-astrocytomas and grade-I and grade-II astrocytomas, respectively. The primary tumour volume did not predict survival. Small residual tumour volumes before RT were, however, associated with a better outcome, although they were strongly related with the more favorable oligodendroglioma histologic subtype. Non-pilocytic astrocytomas and mixed tumors did not show a significant volume-outcome relationship in our study.