IMPACT OF [C-11]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-1-weighted magnetic resonance imaging (Gd-MRI) and T-2-weighted MRI (T-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 ([C-11]MET-PET) findings. Methods and Materials: Computed tomography (CT), MRI, and [C-11]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-2-MRI of the CTV (CTV-T-2) were compared with the extent of [C-11]MET-PET (CTV [C-11]MET-PET) uptake by using CT MRI or CT-[C-11]MET-PET fusion imaging. We defined CTV-Gd (x mm) and CTV-T-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-2, respectively. We evaluated the relationship between CTV-Gd (x mm) and CTV [C-11]MET-PET and the relationship between CTV-T-2 (x mm) and CTV-[C-11] 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-2 (20 mm) (96.4%) was significantly higher than that of The other CTV-T-2 (x = 0, 2, 5, 10 mm). The highest sensitivity and lowest specificity was found with CTV-T-2 (x = 20 mm). Conclusions: It is necessary to use a margin of at least 2 cm for CTV-T-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-2-MRI for the precise delineation of target volumes in radiation therapy planning for postoperative patients with GBM. (C) 2012 Elsevier Inc.