Target Definition For Glioblastoma Multiforme In Radiation Therapy Planning By Two Differential Uptake Values On C11-Methionine Pet

The standard tools in the target volume delineation of glioblastoma multiforme (GBM) are gadolinium enhanced T1-weighted (Gd-MRI) and T2-weighted MRI (T2-MRI), however, neither contrast enhancement nor edema are necessary to accurately measure tumor extension in postoperative patients with GBM. The C11-Methionine PET (MET-PET) is a well-established technique for evaluating the tumor extent for the treatment planning in GBM and there is a local relationship between the MET-PET uptake and the malignant activity. The purpose of this work is to investigate the recognition of the tumor extent in the radiation therapy planning of postoperative patients with GBM using two differential uptake values of MET-PET by comparing Gd-MRI and T2-MRI. A CT, MRI, and MET-PET were separately performed within 1 week in 23 postoperative patients with GBM for the radiation therapy planning. The Gd-MRI clinical target volume (CTV) (CTV-Gd) and the T2-MRI clinical target volume (CTV) (CTV-T2) were defined as the contrast-enhanced area on Gd-MRI and the high intensity area on T2-MRI, respectively. The MET-PET CTV (CTV-MPET1) was defined as the area of an accumulation of MET-PET, which was apparently higher than that of normal tissue on MET-PET. A threshold value of CTV-MPET1 for the tumor/normal tissue index of 2.0 was considered for severe malignant activity. The CTV-MPET2 was defined as the area of an accumulation of MET-PET, which was slightly higher than that of normal tissue on MET-PET images. A threshold value of CTV-MPET2 for the tumor/normal tissue index of 1.3 was considered for mild malignant activity. The mean CTV-Gd, CTV-T2, CTV-MPET1 and CTV-MPET2 were 30.6 cc, 112.0 cc, 6.8 cc and 114.4 cc, respectively. Considering CTV-MPET1 as the gold standard for severe malignant activity, the mean sensitivity, specificity, positive predictive value and negative predictive value of CTV-Gd and CTV-T2 for severe malignant activity were 72.9%, 98.6%, 27.1%, 99.8% and 96.7%, 93.3%, 13.7%, 99.9%, respectively. Considering CTV-MPET2 as the gold standard for mild malignant activity, the mean sensitivity, specificity, positive predictive value and negative predictive value of CTV-Gd and CTV-T2 for mild malignant activity were 39.0%, 99.5%, 80.5%, 94.0% and 73.1%, 97.0%, 57.4%, 96.8%, respectively. In postoperative patients with GBM, the abnormalities found on Gd-MRI and T2-MRI differed considerably from the uptake value of MET-PET. In the place of Gd-MRI and T2-MRI, MET-PET using two differential uptake values may be more useful for defining the target volume in the radiation therapy planning of postoperative patients with GBM.