Association of ¹¹C-Methionine PET Uptake With Site of Failure After Concurrent Temozolomide and Radiation for Primary Glioblastoma Multiforme

Purpose: To determine whether increased uptake on 11C-methionine-PET (MET-PET) imaging obtained before radiation therapy and temozolomide is associated with the site of subsequent failure in newly diagnosed glioblastoma multiforme (GBM). Methods: Patients with primary GBM were treated on a prospective trial with dose- escalated radiation and concurrent temozolomide. As part of the study, MET-PET was obtained before treatment but was not used for target volume definition. Using automated image registration, we assessed whether the area of increased MET-PET activity (PET gross target volume [GTV]) was fully encompassed within the high-dose region and compared the patterns of failure for those with and without adequate high-dose coverage of the PET-GTV. Results: Twenty-six patients were evaluated with a median follow-up of 15 months. Nineteen of 26 had appreciable (>1 cm³) volumes of increased MET-PET activity before treatment. Five of 19 patients had PET-GTV that was not fully encompassed within the high-dose region, and all five patients had noncentral failures. Among the 14 patients with adequately covered PET-GTV, only two had noncentral treatment failures. Three of 14 patients had no evidence of recurrence more than 1 year after radiation therapy. Inadequate PET-GTV coverage was associated with increased risk of noncentral failures. (p < 0.01). Conclusion: Pretreatment MET-PET appears to identify areas at highest risk for recurrence for patients with GBM. It would be reasonable to test a strategy of incorporating MET-PET into radiation treatment planning, particularly for identifying areas for conformal boost.