Radiotherapy for high-grade gliomas. Does altered fractionation improve the outcome?

BACKGROUND AND PURPOSE

The publication of Radiation Therapy Oncology Group (RTOG) Study 83-02 in 1996 stimulated further investigations of altered fractionation, i. e., application of more than one fraction per day, in high-grade gliomas. This review summarizes the results of trials published between January 1997 and June 2002.

MATERIAL AND METHODS

To identify suitable trials, a Medline search was performed by use of the following key words: brain tumors/astrocytoma/glioma/high-grade glioma/malignant glioma/glioblastoma multiforme and accelerated radiotherapy/hyperfractionated radiotherapy/altered fractionation. In addition, the search was extended to reference lists of articles and textbooks. Whenever possible, data were extracted from the original papers on an intention-to-treat basis, i. e., patients with protocol violations were not excluded for the purpose of this analysis. Studies in brain stem gliomas, pediatric patients and studies which achieved acceleration by radiosurgery, stereotactic radiotherapy, or brachytherapy rather than conventional external-beam treatment were not included. An exploratory analysis of 2-year survival was also performed. For this purpose, the 2-year survival rate was extracted from each individual study. The total number of 2-year survivors was then calculated for each treatment strategy and compared by use of the chi(2)-test.

RESULTS

The authors identified 1,414 patients from 21 studies; two of these were randomized phase III studies. In seven studies (658 patients), chemotherapy or radiosensitizers were not administered in addition to radiotherapy. The others provide a very heterogeneous set of data, because a large variety of drugs and administration schedules was used. Seven studies included patients with glioblastoma multiforme only, two were limited to patients with anaplastic gliomas. Dose per fraction was 1.2-1.8 Gy in 17 studies and 1.9-2.65 Gy in four. Overall treatment time was 12-31 days, except for one study. Three out of five studies where three fractions per day were administered, included a 2-week break (split-course studies). None of the studies reported a significant improvement in survival by altered fractionation in comparison to either institutional historical controls or their respective randomized control arm. Doses of 60-70 Gy do not appear to improve survival compared to 50-60 Gy. The current data provide no arguments for use of three instead of two fractions per day. Median survival was 10 months after radiotherapy alone (658 patients) and 11 months after combined treatment (756 patients). Regarding 2-year survival rates, radiotherapy alone resulted in 13%, combined chemoradiation or use of sensitizers in 23% (p < 0.0001). However, prognostic factors such as tumor histology were not equally distributed and favor the combined-treatment group. Evaluation of six studies of conventional radiotherapy alone resulted in data from 571 patients. Their median survival was 10.8 months. Cumulative 2-year survival amounted to 15%. The studies of conventional radiotherapy plus chemotherapy or sensitizers included 1,115 patients with a median survival of 11 months (2-year survival rate 18.5%).

CONCLUSION

Altered fractionation shortens the overall treatment time for adult patients with supratentorial high-grade gliomas. However, there is no significant survival improvement.