Bihemispheric malignant glioma: one size does not fit all.

Recurrence of malignant glioma following radiotherapy most commonly occurs in close proximity to the original contrast enhancing CT/MRI tumor volume. For this reason current radiation planning favors focal radiotherapy fields designed to cover the preoperative tumor contrast enhancing volume +/- surrounding edema with a 2-4 centimetre margin. Two patients with bifrontal malignant gliomas treated with such radiotherapy fields experienced out of field tumor progression while on treatment. Posterior extension along the corpus callosum, not evident on pretreatment imaging, was hypothesized as the cause of the geographic miss. The literature documenting recurrence patterns of malignant glioma following radiotherapy support focal field radiotherapy fields for most patients with malignant glioma. Reporting bias may exist in the literature, however, due to the whole brain radiotherapy used in older series reporting recurrence patterns and exclusion of patients with bihemispheric or more locally extensive tumors in more modern series. Tumor location and pattern of growth at presentation may be important factors in predicting patterns of spread and relapse after radiotherapy.