High dose conformal radiotherapy with rotational multi-leaf collimator for glioblastoma multiforme: treatment results and multivariate analysis

Purpose: Survival of patients with glioblastoma multiforme is extremely poor. Although this tumor is clearly radiation resistant, there is evidence of a dose response relationship. The purpose of the study is to evaluate the impact of higher dose delivered with the rotational multi-leaf collimator (MLC) conformal radiation therapy. Methods and Materials: From 1984 to 1995, 35 consecutive cases with histologically confirmed glioblastoma multiforme in the brain were treated using the rotational multi-leaf collimator conformal therapy which is a combined continuous gantry rotation and MLC movement. There were 23 males and 12 females with a median age of 45.3 years (12 to 73 years). Mean Karnofsky performance score was 78 (30-100). Mean tumor volume at the time of diagnosis was 104 cc (8-800 cc). All cases underwent surgical intervention prior to radiation therapy (biopsy only in one, partial resection in 13, and subtotal resection in 18, and gross total resection in three). Residual tumor volume ranged from 0 cc to 567 cc with an average of 35 cc. Radiation dose was 60 to 80 Gy (mean 68.3 Gy) in 21 cases before 1992 and 90 Gy in 14 cases after 1992, with an overall mean dose of 77 Gy. Before 1992, the rotational multi-leaf collimator conformal therapy was combined with whole brain radiation of 30 Gy, whereas the latter was replaced by a generous field rotational conformal therapy after 1992. Dose fall-off proportional to the target volume was achieved using three-dimensional treatment planning in all cases. Biweekly intravenous administration of ACNU and Vincristin was combined. Results: As for radiation toxicity, only one case developed and died of late brain edema four months after the completion of therapy with 90 Gy. The one-year, three-year, and five-year survival rates were 64 %, 36 %, and 21 % respectively, with a 50 % survival time of 17 months. Two survived more than five years. Univariate analysis showed initial tumor volume, residual tumor volume, and Karnofsky performance score were statistically significant factors for survival. Only residual tumor was statistically significant by multivariate analysis. Five-year survival rate of cases with tumors 2 cm or less in diameter was as good as 47 %. Conclusions: The rotational MLC conformal therapy in combination with intensive surgical resection provided favorable treatment results as compared to those reported so far