This case demonstrates that multiple courses of re-irradiation are feasible and may lead to improvement in quality of life and increased survival. Clinicians are reluctant to offer additional radiation therapy for recurrence both because of apprehension of exceeding normal structure tolerance as well as lack of evidence supporting this practice. Exceeding the dose that can typically be tolerated by a given structure can affect both short term and long term toxicity. This is particularly relevant when treating recurrent gliomas as tumors typically recur within close proximity to the original location where high doses of radiation have typically been delivered to the area of recurrence. In addition, the infiltrative nature of high-grade gliomas requires large margins when using standard external beam irradiation.
Both fractionated and single fraction stereotactic radiosurgery have been studied in re-irradiation of recurrent tumors. Stereotactic Radiosurgery (SRS) utilizes a steep dose gradient to deliver a highly conformal non-invasive single dose of radiation [4
]. It is more commonly used for smaller treatment volumes and has also demonstrated reasonable median survival times after radiosurgery in very highly selected patients [5
]. Radiation-induced necrosis in these studies was prevalent in studies where larger tumor volumes were treated.
Fractionated radiation therapy uses the same precision as radiosurgery but allows greater protection of normal structures while delivering an equivalent dose of radiation by delivering the dose over multiple treatment days. The largest study examining the efficacy and tolerability of fractionated radiation therapy consisted of 172 patients and demonstrated promising survival results with minimal rates of radiation induced side effects [9
]. Other studies have also demonstrated similar survival rates with minimal toxicity in addition to improvement in neurological symptoms [10
In our case, multiple courses of irradiation were able to be delivered following initial treatment in part because the residual areas to be treated were located at different positions along the periphery of the tumor that could be individually targeted (see Figure ). While our patient was at risk for necrosis within the tumor bed, it is important to recognize that necrosis is considered a therapeutic effect of radiosurgery and the important component of treatment with respect to clinical outcomes is the sparing of normal tissue. By re-irradiating the recurrence at the edge of the tumor bed, we were able to treat the tumor recurrence and avoid normal tissue.
We acknowledge that the histopathologic grading of oligodendrogliomas is controversial and subject to interobserver variability. To the best of our knowledge, our patient was diagnosed with a WHO grade IV oligodendroglioma. Grade IV oligodendrogliomas essentially appear to be glial neoplasms with overwhelming features of glioblastoma multiforme (GBM) arising from known lower grade oligodendrogliomas or GBM with a significant proportion of oligodendroglial differentiation. The diagnostic utility of this diagnosis is uncertain as these tumors may behave either like glioblastoma or grade III oligodendrogliomas.
The updated WHO guidelines published in 2007 recommend classifying such tumors for the time being as 'glioblastoma with oligodendroglioma component'. It remains to be established whether or not these tumors carry a better prognosis than standard glioblastomas and we, therefore, chose to focus our case on the feasibility of delivering multiple courses of radiation rather than the prolonged survival of our patient.