When one looks at the issue of radiotherapy for low grade gliomas, one sees the opposite type of paradigm as one sees with surgery. And that’s for the low-grade astrocytomas radiation therapy does not appear to make a significant different in either a five- or ten-year survival, and that may be because surgery is such a good therapy for these patients. On the other hand, for the grade II astrocytomas where surgery is less effective, or appears to be less effective by the data, one sees a significant benefit from radiation therapy. Thus, we generally do recommend external beam radiation therapy for patients with most low-grade astrocytomas. There again, the dose of radiation, whether one should radiate at the time of diagnosis or wait until time to progression and/or symptoms, remain unknown answers at this time.
The more common astrocytomas are high-grade astrocytomas, which are bad tumors. These are rapidly growing, infiltrative and destructive lesions. Radiographically on CT scan they appear as low-attenuating, contrast-enhancing masses. On MRI scans they appear as increased P2 signal representing both tumor and edema, and they are gadolinium enhanced. Death from these tumors is both from local cerebral destruction and increased intracranial pressure. A type I tumor is a tumor where almost all the tumor cells are confined within one relatively localized area, and one can imagine that if the neurosurgeon has access to this lesion, if he can take this lesion out that would be pretty good therapy. In fact, this is how many or most metastatic brain tumors grow, and that is the reason that there is a significant benefit often for the surgical resection of metastatic lesions.
Unfortunately, most primary brain tumors such as astrocytomas and other gliomas do not grow like type I tumors, but rather they grow like type II or type III tumors. And that the essential area of high tumor density and tumor mass. At great distance away from that mass are these infiltrating tumor cells that reach deeply into the normal and functioning cerebrum, and that total surgical resection is never possible because these lesions get into critical areas of the brain. In fact, with astrocytomas, one can even see the most exaggerated form of this, the condition known as gliomatosis cerebri where there is no central mass whatsoever but rather almost the entire brain is just full of individual microscopic infiltrating tumor cells.