Impact of [11C]Methionine Positron Emission Tomography for Target Definition of Glioblastoma Multiforme in Radiation Therapy Planning

Purpose: The purpose of this work was to define the optimal margins for gadolinium-enhanced T{sub 1}-weighted magnetic resonance imaging (Gd-MRI) and T{sub 2}-weighted MRI (T{sub 2}-MRI) for delineating target volumes in planning radiation therapy for postoperative patients with newly diagnosed glioblastoma multiforme (GBM) by comparison to carbon-11-labeled methionine positron emission tomography ([{sup 11}C]MET-PET) findings. Methods and Materials: Computed tomography (CT), MRI, and [{sup 11}C]MET-PET were separately performed for radiation therapy planning for 32 patients newly diagnosed with GBM within 2 weeks after undergoing surgery. The extent of Gd-MRI (Gd-enhanced clinical target volume [CTV-Gd]) uptake and that of T{sub 2}-MRI of the CTV (CTV-T{sub 2}) were compared with the extent of [{sup 11}C]MET-PET (CTV--[{sup 11}C]MET-PET) uptake by using CT--MRI or CT--[{sup 11}C]MET-PET fusion imaging. We defined CTV-Gd (x mm) and CTV-T{sub 2} (x mm) as the x-mm margins (where x = 0, 2, 5, 10, and 20 mm) outside the CTV-Gd and the CTV-T{sub 2}, respectively. We evaluated the relationship between CTV-Gd (x mm) and CTV-- [{sup 11}C]MET-PET and the relationship between CTV-T{sub 2} (x mm) and CTV-- [{sup 11}C]MET-PET. Results: The sensitivity of CTV-Gd (20 mm) (86.4%) was significantly higher than that of the other CTV-Gd. The sensitivity of CTV-T{submore » 2} (20 mm) (96.4%) was significantly higher than that of the other CTV-T{sub 2} (x = 0, 2, 5, 10 mm). The highest sensitivity and lowest specificity was found with CTV-T{sub 2} (x = 20 mm). Conclusions: It is necessary to use a margin of at least 2 cm for CTV-T{sub 2} for the initial target planning of radiation therapy. However, there is a limit to this setting in defining the optimal margin for Gd-MRI and T{sub 2}-MRI for the precise delineation of target volumes in radiation therapy planning for postoperative patients with GBM.« less