Advanced PET and MR imaging in re-irradiation of high grade glioma

Primary brain cancer is rare but devastating disease. The cancer infiltrates healthy brain tissue and causes neurological symptoms, seizures and cognitive dysfunction. The treatment is aggressive and may have late adverse effects that mimic the symptoms of the disease. Recurrence is almost inevitable and the goal of all treatment is to prolong life while maintaining quality of life. Radiotherapy is a cornerstone of treatment. In many hospitals repeated irradiation is attempted at
recurrence but neither side-effects nor efficacy have been systematically evaluated using modern technology.
The goal of this Ph.D. project was to evaluate the side-effects and efficacy of re-irradiation of highgrade glioma and to determine the value of positron emission tomography (PET) using an amino acid tracer for re-irradiation. Moreover, to identify imaging biomarkers capable of predicting the clinical course following radiotherapy. Two prospective studies were carried out; a Phase I/II study of re-irradiation to patients with progressive high-grade glioma and an observational study where tumor blood perfusion was measured using magnetic resonance imaging (MRI) in the course of radiotherapy. The patients in the re-irradiation study underwent cognitive testing as a means of assessing side effects.
The studies showed that the side effects of re-irradiation were acceptable but not negligible. Tumor size evaluated by PET was prognostic for survival following radiotherapy and it PET likely contributed valuable information for use in treatment planning. We were able to describe the cognitive function of the patients in a quantitative way and to document changes prospectively,
which has not previously been described. Tumor perfusion, surprisingly, was shown to increase significantly during early stages of treatment and later decrease. While these changes did not correlate to outcomes, they may form the basis for generation of hypotheses.