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Purpose: This study investigated the clinical impact of (11)C-labeled methionine-positron emission tomography (MET-PET) for stereotactic radiation therapy with intensity modulated radiation therapy (SRT-IMRT) in metastatic brain tumors. Methods and Materials: Forty-two metastatic brain tumors were examined. All tumors were treated with SRT-IMRT using a helical tomotherapy system. Gross tumor volume (GTV) was defined and drawn on the stereotactic magnetic resonance (MR) image, taking into account the respective contributions of MR imaging and MET-PET. Planning target volume (PTV) encompassed the GTV-PET plus a 2-mm margin. SRT-IMRT was performed, keeping the dose for PTV at 25-35 Gy in 5 fractions. The ratio of the mean value of MET uptake to the contralateral normal brain (L/N ratio) was plotted for the PTV prior to SRT-IMRT, at 3 months following SRT-IMRT, and at 6 months following SRT-IMRT. Tumor characteristic changes of MET uptake before and after SRT-IMRT were evaluated quantitatively, comparing them with MRI examination. Results: Mean ± SD L/N ratios were 1.95 ± 0.83, 1.18 ± 0.21, and 1.12 ± 0.25 in the pre-SRT-IMRT group, in the 3 months post-SRT-IMRT group, and in the 6 months post-SRT-IMRT group, respectively. Differences in the mean L/N ratio between the pre-SRT-IMRT group and the 3-month post-SRT-IMRT group and between the pre-SRT-IMRT group and the 6 month post-SRT-IMRT group were statistically significant, irrespective of MRI examination. Conclusions: We showed examples of metastatic lesions demonstrating significant decreases in MET uptake following SRT-IMRT. MET-PET seems to have a potential role in providing additional information, although MRI remains the gold standard for diagnosis and follow-up after SRT-IMRT. The present study is a preliminary approach, but to more clearly define the impact of PET-based radiosurgical assessment, further experimental and clinical analyses are required. [ABSTRACT FROM AUTHOR]

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 ([(11)C]MET-PET) findings. Methods and Materials: Computed tomography (CT), MRI, and [(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(2)-MRI of the CTV (CTV-T(2)) were compared with the extent of [(11)C]MET-PET (CTV--[(11)C]MET-PET) uptake by using CT--MRI or CT--[(11)C]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-- [(11)C]MET-PET and the relationship between CTV-T(2) (x mm) and CTV-- [(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(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. [ABSTRACT FROM AUTHOR]