Radiation treatment planning for malignant astrocytomas

Abstract

Treatment planning for malignant astrocytomas has been an area of controversy for the past 30 years. Several key studies have supported widely divergent treatment philosophies. Before the availability of computerized tomography (CT) scanning, whole brain irradiation (WBRT) was necessary to ensure adequate tumor coverage, due to limitations of less-sophisticated imaging studies. Following the introduction of high-quality CT scanning and magnetic resonance imaging (MRI), there was a shift to the use of more-limited radiation fields to treat only the contrast-enhancing tumor plus a margin. Additional impetus for use of smaller treatment fields came from studies implicating WBRT in cerebral dysfunction in long-term survivors.‘~* Recently, the appeal of limited field irradiation has been tempered by biopsy and autopsy studies that suggest wider migration of malignant cells than previously believed?” There have thus emerged two schools of thought. One is that patients should receive limited field irradiation, with the hope of avoiding mental deterioration in the few long-term survivors. The opposite argument is that patients should receive WBRT in order to treat all potential sites of tumor infiltration in all patients. While both points of view have merit, they must be reconciled with the fact that many patients will die of their disease within 1 year of diagnosis, regardless of the radiation fields used. The bulk of retrospective data available do not show a survival advantage to large versus small field irradiation (for review, see reference 5). The first study to systematically analyze radiation planning for high-grade astrocytomas was published by Concannon et al” in 1960. Partial brain irradiation (PBRT) fields were compared with tumor volumes identified at autopsy in 2 1 patients who died shortly after starting treatment. The fields were designed