Methionine Positron Emission Tomography For Malignant Brain Tumors In Radiation Therapy Planning

The purpose of this work was to define the optimal margins for gadolinium-enhanced T1-weighted magnetic resonance imaging (Gd-MRI) and T2-weighted MRI (T2-MRI) for delineating target volumes in planning radiation therapy for malignant brain tumors by comparison to carbon-11-labeled methionine positron emission tomography (MET-PET) findings. Computed tomography (CT), MRI, and MET-PET were separately performed for radiation therapy planning for 32 newly diagnosed and 25 recurrent patients with glioblastoma multiforme (GBM), 14 anaplastic gliomas (WHO2007), 19 brain metastases over the course of 2 weeks. Among the MRI scans, we used the contrast-enhanced T1-weighted images (Gd-MRI) and T2-weighted images (T2-MRI). The Gd-MRI-based clinical target volume (CTV) (CTV-Gd) and the T2-MRI-based CTV (CTV-T2) were defined as the contrast-enhanced area on Gd-MRI and the high intensity area on T2-MRI, respectively. We defined CTV x mm (x = 2, 5, 10, 15, 20) as x mm outside the CTV. MET-PET-based CTV (CTV-MPET) was defined as the area of accumulation of MET-PET. We calculated the sensitivity and specificity of CTV-Gd and CTV-T2 following comparison with CTV-MPET, which served as the gold standard in this study. In newly diagnosed GBM patients, the sensitivity of CTV-Gd (20 mm) (86.4%) was significantly higher than that of the other CTV-Gd. The sensitivity of CTV-T2 (20 mm) (96.4%) was significantly higher than that of the other CTV-T2 (x = 0-10 mm). The specificity of CTV-T2 (20 mm) was 68%. In recurrent GBM patients, the sensitivity of CTV-T2 (5 mm) (98%) was significantly higher than CTV-T2 (87%). The specificity of CTV-T2 (5 mm) was 89%. In anaplastic gliomas, the sensitivity of CTV-T2 (5 mm) (96%) was significantly higher than CTV-T2 (85%). The specificity of CTV-T2 (20 mm) was 86%. In brain metastases patients, the sensitivity of CTV-Gd (2 mm) (98%) was significantly higher than CTV-Gd. It is necessary to use a margin of at least 2 cm around the high intensity area on T2-MRI for the initial target planning of newly diagnosed GBM, and 5 mm around the high intensity area on T2-MRI for the target planning of recurrent GBM and anaplastic gliomas, and 2 mm outside the Gd enhanced area in the coverage of MET-PET findings.