Purpose: Irradiation remains the cornerstone of management for glioblastoma multiforme. The Radiation Therapy Oncology Group and European Organization for Research and Treatment of Cancer advocate encompassing the primary tumor plus a 2-cm margin in the high-dose volume. One shortcoming of this approach is the exposure of critical structures to radiation doses that could exceed organ tolerance. We investigated whether the temporal bone (rather than the aforementioned 2-cm radius) would serve as a barrier to tumor spread when regarded as the anterior margin for temporal lobe lesions. We hypothesized that by using the temporal bone as the radiation field margin, toxicity could be reduced without compromising tumor control.
Methods and materials: Between 2003 and 2007, 342 patients with newly diagnosed glioblastoma multiforme were treated with surgery and primary irradiation at our institution. Of these 342 patients, 50 had lesions confined to the temporal lobe. The clinical target volume included the primary lesion, the area of edema when present, and a 2-cm margin, except in the direction of the temporal bone.
Results: Of the 50 patients, 40 were available for evaluation. At a median follow-up of 12.95 months, 8 patients had not yet shown signs of tumor progression, 24 had local failure, 7 had distant or mixed (local plus distant) failure, and only 1 patient had failure in the infratemporal fossa.
Conclusions: The results of the study have demonstrated an acceptable level of recurrence when the temporal bone, rather than a 2-cm margin, is used as the anterior border of the clinical target volume. The strategy we have proposed achieves tumor control and respects optic tolerance without resorting to complex, expensive approaches such as intensity-modulated radiotherapy.