Irradiation fields and doses in glioblastoma multiforme: Are current standards adequate?

Aims and background: The optimum conventional radiotherapy in glioblastoma multiforme patients has not been clearly defined by prospective trials. To better characterize a standard radiotherapy in glioblastoma multiforme, the impact on survival of different fields and doses was analyzed in a retrospective single center series. Methods: One hundred and forty-seven patients with glioblastoma multiforme, submitted to biopsy only (n = 15), subtotal (n = 48) or total resection (n = 82) and who completed the planned postsurgical radiotherapy, were considered. The median age was 57 years, the male/female ratio 1.5/1, and the performance status greater than or equal to 70 in 76%. Whole brain irradiation, followed by a boost to partial brain, was used in 75 cases with a whole brain dose of 44-50 Gy (median, 46) and a partial brain dose of 56-70 Gy (median, 60 Gy). Partial brain irradiation alone was used in 72 patients with a dose of 56-70 Gy (median, 61 Gy). Ninety-eight patients received 56-60 Gy (median, 59 Gy) to partial brain whereas 49 patients received 61-70 Gy (median, 63 Gy). Results: There was an almost significantly longer survival in patients irradiated to the partial brain alone with respect to those also receiving whole brain radiotherapy (P = 0.056). Doses > 60 Gy significantly prolonged survival (P = 0.006). Multivariate analysis confirmed that the impact on survival of radiation dose was independent of age, performance status, extent of surgery, field of irradiation and the use of chemotherapy. The extent of irradiation field was not independently related to improved survival. Conclusions: Our retrospective findings suggest that we reflect on the adequacy of the current standard irradiation parameters. Well-designed prospective trials are necessary to standardize the radiotherapy control group in patients with glioblastoma multiforme to be compared in phase III trials with innovative therapeutic approaches.