Primary Cerebral Tumor Evaluation with PET/CT Using C-11 Methionine

Introduction

C-11 Methionine PET shows high tracer uptake in primary as well as recurrent malignant brain tumors due to increased amino acid metabolism in malignant tissue. The sensitivity of C-11 Methionine PET for cerebral tumors has been reported to be very high when compared to FDG PET, which often shows low or absent uptake in similar tumors. Methionine PET provides good contrast in tumors, since background uptake of amino acids in normal brain tissue is low. Small tumors and early tumor recurrences show high C-11 Methionine uptake, which helps differentiating tumorous from non-tumorous conditions, distinguishing tumor recurrence from post radiation necrosis, and correlating the tumor grade in Gliomas.

The higher sensitivity of C-11 Methionine PET as compared to MRI for cerebral tumors is well documented. In one study of 22 pediatric patients with low grade brain tumors, C-11 Methionine PET improved tumor delineation and contributed to define a final target tumor contour different from that obtained with MRI alone and led to improvement regarding the amount of tumor removed.(1)

History

A 45-year-old male patient presented with gradually progressive loss of sensation in the left side of his face, forehead, and scalp for two months. Loss of sensation was accompanied by gradual hearing loss in right ear. Initial CT and MRI studies suggested a lesion of the right parietal cortex with surrounding edema. The patient was referred for an FDG PET/CT study, which showed low uptake in the area suspicious of tumor tissue. In order to further characterize the suspected tumor and to look at the true extent of the tumor and its grade, a C-11 Methionine PET/CT was performed. Study performed on a Biograph™ 16 system following injection of 10 mCi C-11 Methionine with a post injection delay of 20 min.

Fig. 1: Sagittal, coronal, and axial PET/CT fused images of FDG study shows decreased uptake of FDG in right parietal cortex in area suggestive of space occupying lesion on CT and MRI. Comparison of normal FDG uptake in the contralateral cortical sulci shows the relative decrease in FDG uptake in the region of clinical interest.

Fig. 2: Sagittal, coronal, and axial PET/CT fused images and volume rendered image of C-11 Methionine PET/CT study shows high uptake in the right parietal cortical tumour with very low uptake in the edema surrounding the tumour and the normal brain parenchyma. C-11 Methionine clearly demonstrates tumor margins.

Diagnosis

This study demonstrates the usefulness of C-11 Methionine, which is highly sensitive and specific for primary brain tumor especially glioma, cerebral metastasis as well as tumor recurrence. The clear delineation of tumor margins in spite of extensive surrounding edema helps define surgical resection margins and tumor volume for precise irradiation. The high degree of uptake of C-11 Methionine in the primary tumor in this patient along with the extensive peritumoral edema suggests a very aggressive nature of the primary glioma.

Comments

Grading of primary tumor using C-11 Methionine is particularly useful in low grade gliomas because the degree of C-11 Methionine uptake accurately predicts the tumor’s time to progression. In one study of 27 patients with grade 2 glioma(3), 93% experienced tumor progression after a median of 103 weeks and all had low uptake of C-11 Methionine in the PET study. Low uptake of Methionine was a predictor for long TTP in patients with oligodendrogliomas, but not in astrocytomas/oligo-astrocytomas. C-11 Methionine PET is also highly useful as a follow-up tool after surgery and radiotherapy in intra-cerebral tumors – primarily as a reliable technique for early differentiation between recurrent brain tumor and treatment-induced nonneoplastic changes. In one study(2) involving 72 patients with confirmed diagnosis of recurrent brain tumor subjected to C-11 Methionine PET, the sensitivity and specificity of PET scanning in detecting tumor recurrence were found to be 95.8% and 96.5% respectively. The increased C-11 Methionine uptake in the initial tumor area was characteristic of recurrent tumor. Brain tissue histological changes associated with surgery, radiation, and chemotherapy were characterized by the low uptake of the tracer. Another study(4) using C-11 Methionine PET and Gadolinium-enhanced MR fusion in post operative patients of cerebral glioma for delineation of tumor recurrence and gross tumor volume definition for radiation therapy showed that 74% of patients had C-11 Methionine uptake larger than the area of Gadolinium enhancement in MRI prompting major changes in radiation therapy planning. Thus, MR and C-11 Methionine PET in combination is ideal for management of post operative intracerebral tumor recurrence.

References

1. Integration of [11C] methionine-positron emission tomographic and magnetic resonance imaging for image-guided surgical resection of infiltrative low-grade brain tumors in children – Pirotte et al. Neurosurgery. 2005 Jul;57(1 Suppl):128-39
2. Positron emission tomography in the diagnosis of recurrent growth of brain tumors – Skvortsova et al. – Zh Vopr Neirokhir Im N N Burdenko. 2005 Apr-Jun;(2):3-7
3. Baseline 11C-methionine PET reflects the natural course of grade 2 oligodendrogliomas – Ribom et al. – Neurol Res. 2005 Jul;27(5):516-21
4. 11C methionine positron emission tomography for target delineation in resected high-grade gliomas gliomas before radiotherapy – Grosu AL, Schwaiger M et al. – Int J Radiat Oncol Biol Phys. 2005 Sep 1;63(1):64-74

Data courtesy of Huashan Hospital, Shanghai, China
Biograph 16